英語讀物：Medical Microbiology
掌握好一門外語，多一把打開醫(yī)學(xué)科學(xué)之門的鑰匙!
At glance at any newspaper confirms the central role of microbiology inall
of ou
r lives.Will there be a vaccine for AIDS? Can genetically engineeredbacteria be
put to work cleaning up oilspills or making anticancer agents? Can we continue
to develop antibioticsfaster than bacteria can evolve with resistance to them?
Will other scourges follow smallpox into the history books,leaving thehuman rac
e finally free of major epidemicsor will new killer diseases appear totheir p
lace?〖〗
vaccine:疫苗
AIDS：艾滋病
antibiotics:抗生素
smallpox：天花
epidemics:流行病
Such questions demonstrate that today microbiology remains one of themost r
elev
ant of the sciences.Microbiology has long been intimately involved withmatters
of life and death,and this is no less true in the age of AIDS than itwas more t
han a century ago,when Pasteur was developing the first modernvaccines.But micr
obiology today is also on the cutting edge of scientific advance,as itwas in th
e seventeenth century when Leeuwenhock was making his simple microscopesand gli
mpsing the microbial world for the first time.Genetic engineering,forexample,wa
s born in the laboratories of microbiologists and spent its youththere.In count
less areas,from agriculture to evolution,from ecology todentistry,microbiology
is both contributing to scientific knowledge and solving human problems.〖〗
Pasteur：巴斯德
Leeuwenhock：列文虎克
Chapter 1. An Overview of Microbiology
After completing this chapter you should be able to
●Define microorganism
●List the major groups of organisms studied in medicalmicrobiology
●Identify the contributions to microbiology made byLeeuwenhoek,Paste
ur,Koch,Ehrlich and Fleming
Microbiology is the study of microorganisms,which are minute livingthings,i
ndiv
idually too small to be seen with the naked eye,and exist as singlecells or cel
l clusters.Microbial cells are thus distinct from the cells of animalsand plant
s,which are unable to live alone in nature but can exist only as parts ofmultic
elluar organisms.A single microbial cell is generally able to carry outits life
processes of growth,energygeneration and reproduction,independently of other c
ells,either of the same kinds or of different kinds.〖〗
microorganisms：微生物
reproduction：繁殖
Today,we casually accept the fact that microorganisms are found almosteve
ryw
here.There are more than 100,000 species of microorganisms in theearth.Based on
the differences of theirstructures and chemical compositions,microorganisms in
the medical microbiology areclassified into bacteria,mycoplasma,rickettsia,spi
rochete,chlamydia,actinomyces,viruses and fungi.〖〗
bacteria:細(xì)菌
virus:病毒
fungi：真菌
Microorganisms are part of the human environment and are therefore important
to
human health.For the few microbes that cause disease,learning how suchdiseases
a
re transmitted and how to diagnose,treat and prevent them is of greatimportance
in a health sciencecareer.Such knowledge will help you care of patients and av
oid becoming infected youreslf.〖〗
microbes:微生物
The First Observations
In 1673,the Dutch amateur microscope builder Leauwenhock was the firstto ob
serve
and describe the “animalcules” through his simple,singlelensmicroscope.Pro
gress in understanding the tiny organisms came quickly only in thenineteenth ce
ntury when improved microscopes became available and wildlydistributed.Better m
i
croscopes have enable scientists to penetrate ever deeped into themysteries of
t
he cell.Several workers discovered ways to stain microorganisms withdyes to mak
e them more visible.〖〗
microscope：顯微鏡
stain:染色
Microbiology as a science didn′t develop until the latter part of theninet
eent
h century.This delay occurred because,in addition to microscopy,certainbasic te
chniques for the study of microorganisms needed to be devised.Investigationof t
he nature of contagious disease led to the development of thesetechniques and l
aid the foundation of microbiological science.〖〗
contagious:傳染的
Fermentation
In 1860,a group of French merchants asked Pasteur to find out why wineand b
eer
soured.They hope to develop a method that would prevent the spoiling ofthose be
verages shipped long distances.Pasteur found that microorganisms calledyeasts c
onvert the sugars to alcohol in the absence of air.This process iscalled fe
rmenta
tion and is used to make wine or beer.Souring and spoiling,which occurlater,are
caused by a different groupof microorganisms,called bacteria.In the presence
of air,bacteria change the alcoholic beverage into sour waste productknown as a
cetic acid.〖〗
yeast：酵母菌
fermentation：發(fā)酵
acetic acid:醋酸
Pasteur′s solution to spoilage was to heat the alcohol just enough tokill
most
of the bacteria,this processdoes not greatly affect the flavor of wine or beer
.
We call this process Pasteurition,and it is used for milk as well assome alcoho
lic drinks to kill bacteria.〖〗
Pasteurition：巴斯德
消毒
The Germ Theory of Disease
The realization that yeasts plays a crucial role in fermentation was thefir
st c
oncept to link a microorganisms′ s activity to physical and chemicalchanges in
organic materials.This discovery altered scientists to the possibilitythat micr
oorganisms might have similar relationships with plants and animalsspecificall
y that microorganisms might invade other organisms and cause disese.Thisidea wa
s called the germ theory of disease.〖〗
germ：病原菌
The first proof that bacteria actually cause disease was given by Kochin 18
76.Ko
ck discovered rodshaped bacteria now termed Bacillus anthracis in thatblood of
cattle that had died of anthrax.He cultured the bacteria on artificialmedia and
t
hen injected samples of the culture into healthy animals.When theseanimals beca
me sick and died,Koch isolated the bacteria in their blood and comparedthem to
t
he bacteria originally isolated.He found that the two sets of bloodculturing co
ntained the same bacteria.〖〗
Koch:科赫
Bacillus anthracis
炭疽桿菌
medium.media(復(fù)數(shù))：
培養(yǎng)基
culture:培養(yǎng)
Koch thus established a sequence of experimental steps for directlyrelating
a s
pecific microbe to a specific disease.These steps are actually a set ofcriteria
,known today as Koch′s Postulates:〖〗
Postulates:定理
1.The same pathogen must always be present in every case of the diseas
e.
2.The pathogen must be isolated from the disease host and grown in pur
e culture.
3.The pathogen from the pure culture must cause the same disease when
introduced into a healthy,susceptible laboratory animal.
4.The pathogen must again be isolated from the introduced animal and m
ust be shown to be the original organism.〖〗
pathogen:病原體
host:宿主
pure culture：純培養(yǎng)
Koch′s postulates provided a tremendous spur for the development of thesci
ence
of microbiology by stressingthe use of laboratory culture.In order to successf
ully study the activities of a microorganism,such as a microorganismwhich cause
s a disease,one must be pure.Without objects as small as microorganismsascertai
ning purity is not easy,for even a ve高級(jí)職稱考試網(wǎng)ry tiny sample of blood or animalfluid may
contain several kinds oforganisms that may all grow together in culture.〖〗
Koch realized the importance of pure cultures.He developed severalingenious
met
hods of obtaining them,of which the most useful is that involving theisolation
of single colonies.He inferred that colony had arisen from a singlebacterial ce
ll that fell on the solid nutrient medium surface.In the 20 yearsfollowing the
formulation of Koch′s postulates,the causal agents of a variety ofcontagious d
iseases were isolated,forexample,C.diphtheriae,V.cholera,T.bacillus,Strep.pneum
oniae.〖〗
single colony：單菌落
Vaccination
In 1798,almost 70 years before Koch established that a specificmicroorganis
ms c
auses anthrax,Jenner embarked on an experiment to find a protection fromsmallpo
x.〖〗
Jenner：琴納
When a young milkgirl told Jenner that she could not get smallpoxbecause sh
e al
ready had been sick from cowpox,he decided to put the girl′s story to atest.Fi
rst Jenner collected scrapings from cowpox blisters.Then he madeinoculations wi
th the cowpox material by scraping the patient′s arm with a poxinfectedneedle.
T
he scratch would turn into a raised bump,in a few days the patient wouldbecome
mildly sick and recover,and would never contract either cowpox orsmallpox again
.We now know that cowpox and smallpox are caused by viruses.Because thecowpox v
irus closely resembles the smallpox virus,it induces immunity withoutgiving hum
ans deadly infection.The process was called vaccination from the Latinword “va
ca”for cow.Theprotection from disease provided by vaccination or by recovery f
rom the disease itself is called immunity.〖〗
cowpox：牛痘
inoculation：接種
vaccination：疫苗接種
Pasteur contributed significantly to the emergence of immunity with hiswork
on
vaccines for cholera and rabies.In 1879,when Pasteur was using chickensas his e
xperimental animals to study cholera,he accidentally used an old choleraculture
to inoculate somechickens.The chickens did not develop disease symptoms.When h
e later inoculated the same chickens with a fresh choleraculture,they remained
healthy.Though he hadn′tplanned to use the old culture first,he did realize t
hat the chickens had been immunized against cholera.Pasteur reasonedthat the or
ganisms must have lost their ability to produce disease but retainedtheir abili
ty to produce immunity against subsequent infections by their virulentcounterpa
rts.〖〗
cholera:霍亂
rabies：狂犬病
Now,some vaccines are still produced from avirulent microbial stainsthat st
imul
ate immunity to the related virulent strain.Other vaccines are made fromkilled
virulent cells or from isolated components of virulent microorganisms.Researcher
s
have recently appliedrecombinant DNA techniques to the development of vaccines
against a variety of virusesincluding those that cause herpes,heapatitis B and
influenza.〖〗
herpes:皰疹
heapatitis:肝炎
The Birth of Modern Chemotherapy:
Dreams of a “MagicBullet”
After the relationship between microorganisms and disease wasestablished,th
e ne
xt major focus for medical microbiologists was the search for substancesthat co
uld destroy pathogenic (diseasecausing) microorganisms without damagingthe
infected animal or human.The treatment of disease by chemical substanceis calle
d chemotherapy.〖〗
chemotherapy：化學(xué)療法
Ehrlich is recognized as the imaginative thinker who fired the firstshot in
the
chemotherapy revolution.As amedical student,Ehrlich speculated about a “magic
bullet” that could hunt down and destroy apathogen without harming the infect
ed host.Ehrlich coined the term chemotherapy and launched a search forsuch a bu
llet,and in 1910 he found a chemotherapeutic agent called 606,an arsenicderivat
i
ve effective against syphilis.In 1935 the sulfa drugs were discovered by Domagk
.Extensions of Domagk′s work led to the development of isoniazid,aneffective a
gent against tuberculosis.〖〗
syphilis:梅毒
sulfa:磺胺
isoniazid:異菸肼
tuberculosis：結(jié)核
In contrast to the sulfa drugs,the first antibiotic was discovered byaccide
nt.W
hen culturing bacteria,Fleming almost tossed out some culture platesthat had be
en contaminated by mold.Fortunately,he took a second look at the curiouspattern
of growth on thecontaminated plates. There was a clear area around the mold,wh
ere the bacterial culture had stopped growing.The mold was lateridentified as P
enicilium notatum and in 1928,Fleming named its active inhibitorpenicillin.Howe
ver,purification of penicillin proved to be a very difficult task.Thegreat need
for such a drug in world warⅡ,money from the Rochefeller Institute and the ha
rd work of pathologist Florey,biochemist Chain,accomplished thetask.Since then,
many other antibiotics have been found,such as streptomycin andtetracycline.
〖〗
plate：平板
mold：霉菌
penicillin：青霉素
streptomycin：鏈霉素
tetracycline：四環(huán)素
Microbiologist,pharmacologists and clinicians are now working on avariety o
f te
chniques to target antimicrobial drugs.The idea is to attach a drugmolecule to
a socalled bullet,which then travels like a homing device to its target,aspec
ifice site of infected cells.The bullet thus releases the drug,which “attacks”
without hurting nearbynormal cells.Such a method would permit the use of drugs
now regarded as too toxicfor general use.Thus the search for a better targeted
magic bullet continues -perhaps with more success soon to come.Advancesin cell
biology and immunology have provided researchers with information aboutseveral
instruments that eventually might turn chemotherapy into a more potentmedical w
eapon.Future bullets might include the “ghost” or membranes of red blood cells
; a group of highly specific molecules called monoclonal antibodies;immunotoxin
,monoclonal antibodies attached to toxins; and artificial fatty globulesknown a
s liposomes.〖〗
antimicrobial：抗微生物的
monoclonal antibody：單克隆抗體
The inadequate targetting of drug and the lack of antiviral drugs areonly t
wo li
mitations of modern chemotherapy.An equally important problem is theemergence a
nd spread of new varieties of microorganisms that are resistant toantibiotics.
The quest to solve these problems requires sophisticated researchtechniques and
correlated studies neverdreamed of in the days of Koch and Pasteur.But before
w
e continue our discussion of medical techniques that control microbes,weneed to
know more about the microbesthemselves.〖〗
antiviral：抗病毒的
Microbiology today is on the cutting edge of scientific advance.Theoverwh
elming
influence of microorganismsin human society is clear.We have many reasons to b
e
aware of microorganisms and their activities.As Pasteur expressed it :“The role
of the infinitely small isinfinitely large”.〖〗
Chapter 2. Functional Anatomy of Bacterial Cell
After completing this chapter you should be able to
●list the steps in a Gram stain and describe theappearance of a gram
positive and gramnegative cell after each steps.
●Identify the three basic shapes of bacteria.
●Explain the differences in cell wall,stainreaction,pathogencity and
antibiotic sensitivitybetween grampositive and gramnegative cells.
●Identify the functions of bacteria cell structures.
Gram Stain
Microorganisms are too small to be seen with the naked eyes,so they mustbe
obse
rved with a microscope.Modern microbiologists have access to microscopesthat pr
oduce,with great clarity,magnifications anywhere from 10 to thousands oftimes m
ore powerful than those of Leeuwenhock′s simple single lens.〖〗
magnification：放大倍數(shù)
Because most bacteria appear almost colorless through a standard lightmicro
sco
pe,one often must prepare them for observation by fixing and stainingthem.The G
ram stain was developed in 1884 by the Danish bacteriologist Gram.It isone of t
he most useful staining procedures in medical microbiology because itdivides ba
cterium into two large groups:grampositive (G+) and gramnegative(G-).〖
〗
fix:固定
Gram stain:革蘭氏染色
In Gram staining procedure,the heatfixed smear is covered with crystalvio
let.
After a short time,the dye is washed off and smear is covered withiodine.When t
h
e iodine is washed off,both grampositive and gramnegative appear darkviolet
.Next,the slide is washed with an ethanol.This solution is decolorizingagent,wh
i
ch removes the violet from the cells of some species but not fromothers.The alc
ohol is rinsed off and the slide is then stained with safranin,a reddye.〖〗
smear:涂片
crystal violet:結(jié)晶紫
iodine.：碘液
slide：載玻片
The smear is washed again,boltted dry,and examinedmicroscopically.Bacteria
that
retain violet after thealcohol has attempted to decolorize them are classified
as grampositive.Bacteriathat lose the violet color after decolorization are
classified as gramnegative.It turns the gramnegative bacteria pink orred.
〖〗
The following general features of bacteria can be observed with thelight mi
croscope:
1.Almost all bacteria have a semirigid cell wall.
2.If bacteria are motile,their motility is usually achieved by flagel
la.
3.Bacteria are unicellular,although they are frequently found in chara
cteristic groupings,each cell carries out all the functions of theorganism.
4.Most bacteria multiply by binary fission,a process which a single ce
ll divides into two identical daughter cells.〖〗
flagella:鞭毛
unicellular:單細(xì)胞的
binary fission:二分裂
Size,Shape And Arrangement Of Bacteria Cells
There are a great many sizes and shapes among bacteria.Most bacteriafall wi
thi
n a range of 0.20 to 20 μm in diameter,and have one of three basic shapes:the s
pherical coccus;the rodshaped bacillus;and the spiral.In addition tocharacter
istic shapes,many bacteria also are found in distinctive arrangemnts ofgroups o
f cells.〖〗
coccus:球菌
spiral：螺形菌
When cocci divide to reproduce,the cells can remain attacked to oneanother,
they
might not separate.Coccithat remain in pairs after dividing are called diploco
c
ci;Those that divide and remain attached in chainlike patterns arestreptococci
;Those that divide at random planes and form grapelike clusters are staphylococc
i.Those groups are frequently helps in the identification of certaincocci.〖〗
diplococci:雙球菌
streptococci:鏈球菌
staphylococci:葡萄球菌
Structures External to the Cell Wall
In studying human anatomy,we must look carefully at the physicalarrangement
of
organs and tissues in the body.Because all bacteria are unicellular,thestudy of
microbial anatomy brings usto inspect a single cell′s construction:how each
cellular component contributes to the structure of the cell as a whole.〖〗
anatomy:解剖
1.Capsule
Capsule is generally composed of polysaccharides,which are made insidethe c
ell,
excreted to the cell surface, firmly attached to the cell wall.Not allbacterial
species producecapsules;however,capsules are an important mechanism of bacteri
al virulence.Capsules play an important role in protecting pathogenicbacteria
against phagocytosis by cells of host.If bacteria lose theircapsules,they becom
e less infectious and more vulnerable to destruction.〖〗
capsule:莢膜
virulence:毒力
phagocytosis:吞噬作用
2.Flagella
Flagella are long filamentous appendages that propel thebacteria.Bacteria w
ith f
lagella are motile,that is,they have the ability to move on theirown.Motility c
an be seen in bacteria grown in a semisolid “motility medium”, in which movem
ent can be seen outward from the inoculum.Motility is important becauseit allow
s microorganisms to move from place to place in order to obtainnutrition for gr
o
wth and reproduction or escape from toxious macroenvironments.Flagellaoccur on
both Grampositive and Gramnegative bacteria,and their presence can beuseful
in identification.Forexample,they are found on many species of bacilli but rar
ely on cocci.〖〗
inoculum：接種物
3.Pili
Pili are hairlike appendages attached to bacteria cells in much the sameway
s as
are flagella.But pili areconsiderably shorter and thinner than flagella.Pili o
ccur almost exclusively on Gramnegative bacteria and are found on onlya few G
rampositive organisms.〖〗
Pili：菌毛
Bacteria can have two kinds of pili:(1)short,attachment pili or (2)long,sex
pil
i.The attachment pili can adhere to the surfaces of other cells.Piliassociated
with the bacterium,Neisseria gonorrhoeae,help the microb
e to colonize mucous mem
branes. Once colonization occurs,the bacteria are capable of causing thedisease
.The sex pili join two bacterial cells and furnish a pathway prior tothe transf
er of DNA from one cell to another.Such transfers among bacteria causeproblems
for humans because antibiotic resistance can be passed on with the DNAtransfer.
Consequently,more and more bacteria acquire resistance,and humans mustlook for
new ways to control these bacteria.〖〗
Neisseria gonorrhoeae:淋球菌
Cell Wall
1.Function and Composition
The major function of the cell wall is to prevent bacterial cells fromreptu
rin
g when the osmotic pressure inside is greater than that outside the cell.Clinca
lly,the cell wall is important because it is the site of action of someantibiot
ics.〖〗
osmotic：滲透的
The bacteria cell wall is composed of a macromolecular network calledpept
idog
lycan(murein).This peptidoglycan layer is biochemically unique and isnot found
in any eukaryotic cells,so that one of the most important structuralfeatures of
the procaryotic cell is thecell wall.〖〗
peptidoglycan:肽聚糖
eukaryotic:真核的
procaryotic:原核的
As the name implies,there are two portions to the peptidoglycanmolecules ——
a pe
ptide portion and a glycan portion.The glycan portion consists of Nacetylgluco
samine(NAG) and Nacetylmuramic acid(NAM).The NAG and NAM alternate inrows, ea
ch row forming a carbohydrate backbone.To each molecule of NAM isattached a te
trapeptide side chain.Adjacent tetrapeptide side chains may be directlybonded
to each other or linked by apeptide cross bridge consisting of one to five ami
no acids.The backone is the same in all bacterial species,thetetrapeptide side
chains and the peptide cross bridges vary from species to species.
〖〗
tetrapeptide:四肽
cross bridges:交聯(lián)橋
2.Differences Between G+ and G-Bacteria
In most grampositive bacteria,the cell wall consists of several layersof pept
idoglycan connected by peptide side chains and cross bridges.Thisarrangement p
rovides a very rigid framework.The layers of peptidoglycan are considerably thi
cker in grampositive than gramnegative bacteria.
G- bacteria also contain peptidoglycan,but in very small amounts,thepeptidogl
yc
an is probably only a monolayer thick,thus,the cell walls of gramnegativebact
eria are susceptible to mechanical breakage.The peptidoglycan layer issurrounde
d by an out membrane structure,which consists oflipoproteins,lipopolysacchari
de (LPS) and phospholopids,This outer layer is an important barrierbetween the
cell′s interior and certain substances from the environment,includingantibioti
cs
such as penicillins,certaindyes and heavy metals.So,in general,the antibiotic
penicillins are more effective against grampositive bacteria thanagainst gram
negative.〖〗
lipopolysaccharide:脂多糖
A characteristic feature of Gramnegative bacteria is possession ofvarious typ
es of complex macromolecular LPS.So far only one Grampositive,List
eria monocytogenes,has been found to contain an authentic LPS.LPS,al
so known as endotoxin,
consists of core polysaccharides,O－polysaccharide and lipid A. O－polysaccharid
e is called O antigen and helps to distinguish species of gram－negativebacteri
a by immunological means.Lipid A is responsible for the toxic propertiesthat ma
ke any gramnegative infection a potentially serious medical problem.Itcauses
fever and intravascular hemolysis.〖〗
endotoxin:內(nèi)毒素
lipid A:脂質(zhì)A，類脂A
The mechanism for the Gram stain is related to the structure andchemical compos
ition of the cell wall.The intact,thick peptidoglycan layers of the grampositi
v
e cells′ walls prevent the crystal violetiodine from leaving thecells,so the
grampositive bacteriaretain the color of the crystal violet dye.The gramne
gative bacteria have much thinner peptidoglycan layer,probably only amonolayer,
and all out membrane composed most of LPS.This out membrane is mostly removedb
y the ethanol rinse,and the monolayer of peptidoglycan hasdiscontinuities that
allow the crystal violetiodine complex to escape.They are colourlessuntil cou
nterstained with red dye,after which they appear pink.〖〗
counterstain:復(fù)染
3.L Form
When the peptide cross linkage is disrupted,the cell wall is defectiveand cann
o
t adequately protect the bacterial cell against osmotic shock.It is forthe reas
on the antibiotic penicillin is effective in controlling bacteriainfections.Pen
icillin prevents the formation of crosslinkages between thepeptides,resulting
in the production ofdefective cell walls and the death of growing bacteria.
〖〗
Clinically,the cell wall is a good target for certain antimicrobialdrugs,becaus
e the wall is made of chemicals unlike those in eucaryoticcells.Thus,chemicals
that will damage bacterial cell walls or interfere with theirsynthesis,often wi
ll not harm the cells of an animal host.〖〗
synthesis:合成
Removal of the bacteria cell wall be accomplished by hydrolysis withlysozyme or
by blocking peptidoglycanbiosynthesis with antibiotic such as penicillin.In os
motically protective media,such treatment liberate protoplasts from grampositi
ve cells and spheroplasts (which retain the out membrane) fromgramnegative cell
s
.The bacterial cells with defective cell walls are called L forms (namedafter t
he Lister Institute,where they were discovered).〖〗
lysozyme:溶菌酶
biosynthesis:生物合成
protoplast:原生質(zhì)體
spheroplast:圓球體
L forms are difficult to cultivate and usually require a medium that issolidifi
ed with agar as well as having the right osmotic strength.Some L formscan rever
t to the normal bacillary or spirillum from upon removal of the inducingstimulu
s.Thus,they are able to resist antibiotics that interfere with cell wallsynthes
is,so, L form infections are relatively special problems inchemotherapy,their r
eversion to the bacillary from can produce relapses of the overtinfection.〖〗
cultivate:培養(yǎng)
agar:瓊脂
bacillary:桿菌
spirillum:螺形菌
Struetures Internal to the Cell Wall
Plasma Membrane
Cytoplasm
Nucleoid
Endospores
When essential nutrients are depleted,certain grampositive bacteriaform speci
alized “resting”cells called endospores.Endosporesare highly durable,dehydrat
ed bodies with a thick wall.They are formed inside the bacterial cellwall.Relea
sed into the environment,they can survive extreme heat,lack of water andexposur
e to many toxic chemicals.〖〗
endospores:芽胞
An endospore is able to remain dormant for a long time,even hundreds ofyears,bu
t it can convert back into vegetative cell in a matter of minutes whencondition
s become more favorable.A bacterium produces a single endospore,whichmerely hel
ps that organism to survive and is not a means of reproduction.Discoveryof bact
erial endospores was of immense important to microbiology.Knowledge ofsuch rema
rkably heat resistant forms was essential for development of adequatemethods o
f sterilization.〖〗
dormant:休眠的
vegetative:繁殖的
sterilization：滅菌
Chapter 3. Growth and Culturing of Bacteria
After completing this chapter you should be able to
●Define bacterial growth,including binary fission.
●Explain howmicrobes are classified on the basis ofoxygen requiremen
ts.
●Describe how pure cultures can be isolated.
When we talk about microbial growth,we are really referring to thenumber of cel
ls,not the size of the cells.Microbes that are “growing” are increasing in num
ber,accumulating into clumps of hundreds of thousands or populations ofbillions
.For the most part,we are not concerned with the size of an individualcell,beca
use it does not vary much during the cell′s lifetime.
By understanding the conditions necessary for microbial growth,we can predictho
w quickly microorganisms will grow in various situations,and determinehow to
c
ontrol their growth.Microbial populations can become very large in a very sh
ort time,and unchecked microbial growth can cause serious disease andfood spoil
age.
Requirements For Growth
Microorganisms are found in nearly every environment on earth,includingevironme
nts in which no other organisms can survive.The requirements formicrobial growt
h can be divided into two categories：physical and chemical.Physicalaspects inc
lu
de temperature,pH and osmotic pressure.Chemical requirements includewater,sourc
es of carbon and nitrogen,minerals,oxygen and organic growth factors.〖〗
1.Temperature
Microorganisms grow well at rather ordinary temperatures,not muchdifferent from
those favored by higheranimals.However,certain bacteria are capable of growing
in extreme cold or extremeheat, at temperatures that would certainly hinder th
e survival of most higher organisms.Microorganisms are divided intothree groups
on the basis of theirpreferred range of temperature.These are the psychrophile
s (coldloving microbes), thermophiles (heatloving microbes) andmesophiles (
moderate temperatureloving microbes).The optimum temperature for manypathogen
i
c bacteria is about human body (37℃),and incubators for clinicalcultures are u
sually set at about this temperature.〖〗
incubator:培養(yǎng)箱
Temperature is important,not only in providing conditions for microbialgrowth,b
ut also in preventing such growth.The refrigeration of food,usually at 4℃,redu
ces the growth of psychrophiles and prevents the growth of most otherbacteria.H
owever,food and other materials such as blood can support growth of somebacter
ia even when refrigerated.For this reason,materials that can withstandfreezing
are stored at temperatures of 20℃ if they are to be kept for longperiods of
time.
High temperatures also can be used to prevent bacterial growthlaboratory equipm
ent and media are often sterilized with heat,and food is frequentlypreserved by
heating and storing inclosed containers.Bacteria are more apt to survive extre
mes of cold than extremes of heat.
2.pH
Most bacteria grow best in a narrow range of pH near neutrality betweenpH6.5 an
d
7.5. Very few bacteria grow at an acid pH below about 4.0.This is thereason why
a number of foods,such assauerkaraut and cheeses,are preserved by the acids of
bacterial fermentation.〖〗
sauerkaraut:泡菜
When bacteria are cultured in the laboratory,they produce acids that caninterfe
re with desired bacteria growth.To neutralize the acids,chemicals calledbuffers
,are included in the growth medium.The peptones and some amino acids insome med
ia act as buffers,and many media also contain phosphate salts.Phosphatesalts ha
ve the advantage of exhibiting their buffering effect in the pH growthrage of m
ost bacteria.They are also nontoxic;in fact,they provide an essentialnutrients
element.〖〗
buffer:緩沖液
peptone:蛋白胨
3.Nutrients
Besides water,one of the most important requirements for microbialgrowth is a s
ource of carbon,needed for all the organic compounds that make up aliving cell.
Carbon is the structural backbone of living matter.
In addition to carbon,other important elements are needed by microbesfor the sy
nthesis of cellular material.For example,protein synthesis requiresconsiderable
amounts of nitrogen,as well as some sulfur.The synthesis of DNA and RNAalso req
uire nitrogen and some phosphorus,as does the synthesis of ATP.themolecule so i
mportant for storage transfer of chemical energy within the cell.
4.Oxygen
We are accustomed to think of oxygen as a necessity of life.Organismsthat requi
re oxygen to live are called obligate aerobes.Facultative anaerobes canuse oxyg
en when it is present,but are also to continue growth by usingfermentation or a
naerobia respiration when oxygen is not available.Obligate anaerobes arebacteri
a that are unable to use molecular oxygen for energyyieldingreactions.In fact
,most are harmed by it.〖〗
obligate aerobe:專性需氧菌
Facultative anaerobe:兼性厭氧菌
Obligate anaerobe：專性厭氧菌
Growth Of Bacteria
1.Bacteria Division
Bacteria normally reproduce by binary fission,a process in which a celldivides
to produce two equalsized progeny cells.Repeating the process results inthe mul
tiplication of the bacteria population.Bacterial growth proceeds as ageometric
progression,because most bacteria reproduce by binaryfission.Therefore,during a
ctive bacterial growth,the size of the microbial population iscontinously doubl
ing.〖〗
progeny:子代
2.Phases Of Growth
A population of organisms introduced into a fresh nutrientrich mediumdisplays
four major phases ofgrowth:(1)the lag phase,(2)the log phase,(3)the stationary
phase,and (4) the decline ordeath phase.
In the lag phase,the organisms do not increase in number,but they aremetabolica
lly activegrowing in size,synthesizing enzymes,and incorporatingvarious molec
ules from the medium.During this phase the organisms increase in sizeand they c
apture large quantities of energy in ATP.
Once organisms have adapted to a medium,the cells begin to divide andenter an e
xponential or log growth phase.Because the doubling time is constant,alogarithm
ic plot of growth during the log phase is straight line.During thisperiod,cellu
lar reproduction is most active;on the other hand,microorganisms aremore sensit
ive to adverse conditions than they usually are.Many antimicrobial drugsexert t
heir effect by interfering with some important step in the growthprocess,and ar
e therefore most harmful to cells.
If log growth continues unchecked,some startling numbers of cells canarise.For
example,a single bacterium dividing every 20 minutes for two days cantheoretica
lly produce an em.quanxiangyun.cnnormously large population of cells (2114,1 44digit numb
er!).B
ut this does not happen.Eventually,growth slows down,and sooner or laternew cel
ls are produced at the same rate as old cells die,the number of livecells stay
s constant.The culture is then in the stationary phase.
As conditions in the medium become less and less supportive of celldivision,man
y cells lose their ability to divide,and thus the cell die.In this deathphase t
he number of live cells decreases at an exponential rate.
Growth phases are displayed in different ways in colonies growth onsolid medium
.Typically,a cell divides exponentially,forming a small colony atdescendants of
the original cell.The colony grows rapidly at its edges,while cellsnearer its c
enter grow more slowly or begin to die,because they have smallerquantites of nu
trients and are exposed to more waste products.All phases of the growthcurve oc
cur simultaneously in a colony.
Culturing Bacteria
Culturing of bacteria in the laboratory presents two problems.First,apure cult
ur
e of a single species is needed to study an organism′scharacteristics.Second,a
medium must be found thatwill support the growth of the desired organism.Let u
s look at some of the ways these problems are solved.
1.Isolation Pure Cultures
Most infections materials contain several kinds of bacteria.If we wishto study
a particular microorganism,it is necessary to use procedures forisolating and g
rowing individual colonies of microorganisms.The term clone is used inmicrobiol
ogy as synonymous with pure culture.A clone is a collection of cellswhich are a
ll derived from a single cell.〖〗
clone.colony：克隆
The isolation method most commonly used is the streak plate method,whichuses ag
ar
plates-plates of mediumsoidified with agar and sterilized.Bacteria are picked
up on a sterile wire loop,and the wire is moved lightly along the agar surface,d
e
positing streaks of bacteria on the surface.Fewer and fewer bacteria aredeposit
e
d as the streaking continues,and individual organisms are deposited inthe regio
n streaked last.〖〗
streak plate:平板劃線
sterilize:滅菌
After the plate is incubated at a suitable growth temperature for theorganism,s
mall colonies derived from a single organism appear.The wire loop isused to pic
k up a portion of a colony and transfer it to any appropriate sterilemedium for
further study.〖〗
incubate:孵育，培養(yǎng)
2.Culture Media
A nutrient material prepared for the growth of microorganisms in alaboratory is
called a culture medium.Somebacteria can grow well on just about any culture m
edium,other require special media,and still others cannot grow on anynonliving
medium yet developed.The microbes that grow and multiply in or on aculture medi
um are referred to as a culture.
Supposed we want to grow a culture of a particular microorganism,perhapsthe mic
robes from a particular clinical specimen.What criteria must the culturemedium
meet? First of all,it must contain the right nutrients for theparticular microo
rganism we want to grow.it should also contain sufficientmoisture,oxygen and a
p
roperly adjusted pH. So that the culture will contain only themicroorganisms we
add to the medium (and theiroffspring),the medium must initially contain no li
ving microorganisms.Finally,the growing culture should be incubated atthe prope
r temperature.〖〗
specimen:標(biāo)本
When it is desirable to grow bacteria on a solid medium,a solidifyingagent such
as agar is added to themedium,Agar is a complex polysaccharide derived from a
marine alga.Agar has some very important properites that make itvaluable to mic
robiology.Few bacteria can degrade agar,so it remains a solid.Alsoimportant i
s the fact that it melts at about the boiling point of water butremaining in a
liquid state until the temperature,it does not injure bacteria when itis poured
over a bacterial inoculum ina Petri plate.Bacterial suspensions can also be mi
xed with the melted agar so that a uniform suspension of bacteria ismade;this c
an be used for tests of susceptibility and other purpose.〖〗
alga:海藻
degrade:降解
Petri plate:培養(yǎng)皿
suspension:懸液
susceptibility:敏感性
Chapter 4. Control of Microbial Growth
After completing this chapter you should be able to
●Define sterilization and disinfection.
●Describe the physical methods of microbial control.
The scientific control of microbial growth began only about one hundredyears ag
o.Prior to that time,it was not uncommon for massive epidemics to killthousands
of people.In some hospital25% of delivering mothers died of infections carried
by hands and instruments ofattending nurses and physicians.
Lister read about Pasteur′s work with microbes and assumed that thenumber of i
nfected surgical wounds could be decreased through use of proceduresthat preven
ted the access of microbes to the wound.This system,known as asepticsurgery,inc
luded the heat sterilization of surgical instruments and,followingsurgery,the a
pplication of phenol to wounds.The practice so reduced the incidence ofinfectio
us and deaths that other surgeons quickly adopted it 〖〗
aseptic:防腐的
phenol：苯酚
We have come a long way in controlling microbial growth since the timeof Lister
.Today′s procedures are far more sophisticated and effective,are usednot only
to control disease organisms,but also to curb microbial growth thatresults in f
ood spoilage.This chapter will discuss how microbial growth can be controlledby
physical methods andchemical agents.
Sterilization and Disinfection
Sterilization is the killing of all microorganisms in a material or onan object
.When properly carried out, sterilization procedures ensure that evenhighly res
i
stant bacterial endospores and fungal spores are killed.In contrast tosteriliza
tion,disinfection means reducing the number of pathogenic organisms onobjects o
r in materials so that they pose no threat of disease.〖〗
fungal spore:真菌孢子
disinfection:消毒
Physical Methods of Microbial Control
1.Heat
Probably the most common method by which microbes are killed isheat.Heat is the
most wildly applicable andeffective agent for sterilization.It is also the mos
t economical and easily controlled.Heat appears to kill microbes bydestroying t
heir enzymes by denaturation.The heat used in sterilization can beapplied in th
e form of moist heat or dry heat.〖〗
denaturation:變性
One type of moist heat sterilization is boiling.At sea level,boiling(100℃) kil
ls vegetative forms of bacterial pathogens,many viruses,and fungi withabout 10
minutes.Freeflowing steam is the equivalent in temperature to boilingwater.En
dospores and some viruses,however,are not destroyed quickly.The hepatitisvirus
can survive up to 30 minutes of boiling,and some bacterial endosporeshave resis
ted boiling temperatures for more than 20 hours.Boiling is therefore notalways
a reliable sterilization procedure.However,a few minutes of boilingtemperatures
will kill most pathogens andgenerally make food or water safe to eat or drink.
〖〗
vegetative form:繁殖體
To reliably sterilize with moist heat,temperatures above that of boilingwater a
re needed.This high temperature is most commonly achieved by steam underpressur
e in an autoclave.The preferred method of sterilization,autoclaving isused unle
ss the material to be sterilized would be damaged by heat ormoisture.The higher
the pressure in the autoclave,the higher the temperature.Forexample,when free
flowing steam,at a temperature of 100℃,is placed under a pressure of 1atmosphe
re above sea level pressure,that is ,above 15 pounds per square inch,thetempera
ture is increased to 121℃.Steam at 121℃ will kill all organisms andtheir endo
spores in about 15 minutes.or perhaps a bit longer,depending on type andvolume
of material being sterilized.〖〗
autoclave:高壓滅菌鍋
Autoclaving is used to sterilize culturemedia,instruments,dressings,solutions,s
y
ringes and numerous other items that can withstand high temperature andpressure
.〖〗
solutions:溶液
syringe：注射器
One of the simplest methods of dry heat sterilization is directflaming.You will
use this procedure manytimes in the laboratory when you sterilize inoculating
loops and needles.To sterilize the inoculating loop or needle,all youhave to do
is to heat the wire to a red glow.This method is 100% effective.Asimilar princi
ple is used in incineration.This is an effective way to sterilize anddispose of
contaminated paper cups,bagsand dressings.〖〗
flaming:用火焰燒
inoculating loop:接種環(huán)
incineration:焚燒
In the early days of microbiolgy,Pasteur found a practical method ofpreventing
the “sickness” or spoilage of beer andwine.Pasteur used mild heating,which w
as sufficient to kill the organisms that caused the particular spoilageproblem
without seriously damaging the taste of the product.The same principlewas later
applied to milk.In classicpasteurization treatment of milk,the milk was expose
d to a temperature of about63℃ for 30 minutes.Most pasteurization done today
uses higher temperatures,at least 72℃,for about 15 seconds.Thistreatment,known
as hightemperature,shorttimepasteurization,is applied as the milk flows co
ntinuously past a heat exchanger.
2.UV Light
UV light damages the DNA of exposed cells.It causes bonds to formbetween adjace
nt thymines in DNA chains.These thymine dimmers inhibit correctreplication of t
he DNA during reproduction of the cell.The UV wave lengths mosteffective or kil
ling microbes are around 260nm; these wave lengths are specificallyabsorbed by
cellular DNA.UV radiation is also used to control microbes in the air.UVor “ge
rmicidal” lamp iscommonly found in hospital rooms,nurseries and operating room
s.〖〗
thymines:胸腺嘧啶
replication:復(fù)制
germicidal:殺菌的
A major drawback of UV light as a sterilize is that it has lowpenetrability,so
organisms to be killed must be directly exposed to the rays.Organismsprotected
by solids and coverings such as paper,glass and textiles are notaffected. Anoth
er potential problem is that UV light can damage the eyes,and prolongedexposure
to UV light can cause burnsand skin cancer.〖〗
penetrability:穿透力
Chemical Methods of Microbial Control
Chemical agents are used to control microbes on living tissue andinanimate obje
cts.Unfortunately,few chemical agents achieve sterility;most of themmerely red
uce microbial populations to safe levels or remove vegetative forms ofpathogens
from objects.A commonproblem in disinfection is the selection of an agent that
will kill all organisms inthe shortest period of time without damaging the con
taminated material.Just as there is no single physical method ofmicrobial contr
o
l that can be used in every situation,there is no one disinfectant thatwill be
appropriate for all circumstances.〖〗
inanimate:無生命的
sterility:無菌
disinfectant:消毒劑
The more of the following qualities a disinfectant has,the moreeffective it is:
1.Acts rapidly.
2.Attacks all or a wide range of microbes.
3.Is able to penetrate thoroughly the material that is contaminated.
4.Readily mixes with water to form a stable solution or emulsion.
5.Is not hampered by organic matter on the substance to be disinfected
.
6.Is not likely to decompose and thereby lose its activity after expos
ure to light,heat or unfavorable weather.
7.Does not stain,corrode or destroy the object being disinfected.
8.Is harmless to animals if it is to be used as antiseptic and does no
t destroy body tissues or act as a toxin if inhaled or swallowed.〖〗
decompose:分解
corrode:腐蝕
inhale:吸入
The ideal disinfectant should also have a pleasant odor,and beeconomical to use
and safe to transport.
We should also remember that the concentration of a disinfectant willaffect its
action.A disinfectant should always be diluted exactly as suggested bythe manuf
acturer.Solution that are too weak may be ineffective,or bacteriostaticinstead
of bactericidal.On the other hand,solutions that are too strong can bedamagerou
s
to humans who come incontact with them.For example,the recommended optimum con
centration of ethanol is 70%.〖〗
bacteriostatic:抑菌的
bactericidal：殺菌的
Chapter 5. Mechanisms of Pathogencity
After completing this chapter you should be able to
●Define pathogencity and virulence.
●Explain how adherence,capsule,cell wall components andenzymes contr
ibute to pathogenicity.
●Contrast the nature and effects of exotoxin andendotoxin.
Now that you have a basic understanding of the structural and functionalaspect
s of microorganisms,we can consider the ways in which the human body andmicroor
ganisms are related in terms of health and disease.
We all have defense mechanisms that are always operating to keep ushealthy.For
instance,unbroken skin and mucos membranes are effective barriersagainst microb
ial invasion and infection.Tears,saliva and gastric juice also playimportant de
fensive roles.The inflammatory response,phagocytosis and fever areadditional at
tempts to keep us healthy.And under certain conditions,we can produceproteins c
alled antibodies,which combine with particular microorganisms andcontribute t
o their destruction.However microorganisms have properties that makethem pathog
enic,that is capable of causing disease.〖〗
mucos membrane:粘膜
saliva:唾液
gastric juice:胃液
A rather delicate balance exists between our defenses and the diseaseproducing
mechanisms of microorganisms.When our defenses resist the diseaseproducingcap
ab
ilities of the microorganism,we maintain our health.But when the abilityof the
microorganism to cause disease overcomes our defenses.diseaseresults.After the
disease has become established,an infected person can recover completely，suffe
r
permanent damage or die,depending on many factors.
Any parasite capable of causing disease in its host is called apathogen.Pathoge
ns vary in their abilities to disturb health,that is,they displaydifferent degr
ee of pathogenicity.Pathogenicity is the capacity to produce disease ina host.O
n this basis,bacteria can be organized into three major groups：frankpathogen,
opportunistic pathogen and nonpathogen.〖〗
parasite:寄生蟲(菌)
pathngan:病原體
pathogenicity:致病性
opportunistic pathogen:機(jī)會(huì)致病菌
When isolated from a patient,frank pathogen are considered to beprobable agents
of disease (e.g. when thecause of diarrheal disease is identified by the labor
atory isolation of Salmonellaspp from feces). Opportunistic pathogen arethose i
solated from patients whose host defense mechanisms have beencompromised.They m
ay be the agents of disease (e.g.in patients who have been predisposedto urinar
y trace infections with E.coli by catheterization). Finally,somebacteria,such a
s Lactobacillus acidophilus,are conisdered to be nonpathogen,becausethey rarely
or never cause human disease.Their categorization as nonpathogens maychange,how
ever,because of the adaptability of bacteria and the detrimental effectof moder
n radiaiton therapy,chemotherapy,and immunotherapy on resistancemechanisms.In f
a
ct,some bacteria previously considered to be nonpathogens are now knownto cause
disease.〖〗
diarrheal:腹瀉的
Salmonella:沙門氏菌屬
urinary trace:尿路
catheterize:導(dǎo)管插入
Lactobacillus acidophilus:嗜酸乳桿菌
Virulence is the degree of pathogenicity.It is affected by numerousvariables su
c
h as the number of infecting bacteria,route of entry into thebody,virulence fac
tors of the bacterium and specific and nonspecific host defensemechanisms.
In order for a pathogen to cause disease,it must gain access to thehost,adhere
to host tissues,resist or evade host defenses,multiply and damage thehost tissu
e. 〖〗
tissue：組織
How Pathogens Adhere To Host Tissues
To cause infection,many bacteria must first adhere to cells,usuallyepithelial c
ells.If they did not adhere,they would be swept away by mucus and otherfluids t
hat bathe the tissue surface.Many bacteria have evolved attachmentmechanisms,su
ch as pili and hairlike structures (lipoteichoic acid and Mprotein),that reco
gnize and attach the bacteria to cells.For many diseasecausingbacteria,invasi
on of the host′s epithelium is central to the infectious process.Somebacteria
(e.g.Sallmonella species) invade tissues through the junctions betweenepithelia
l cells.Other bacteria (e.g.N.gonorrhoeae) invade the host′s epithelialcells a
nd many subsequently enter the tissues.Some bacteria (e.g.Shigella species) mul
tiply within host cell,whereas other bacteria (e.g.Yersinia enterocolitica)do n
ot.〖〗
adhere:粘附
epithelial:上皮的
attach:粘附
invasion:入侵
N.gonorrhoeae:淋球菌
Shigella:志賀氏菌屬
How Pathogens Resist Host Defenses
1.Surface components
Capsules resists the host′s defenses by impairing phagocytosis,a processby whi
ch certain cells of the body engulf and destroy microbes.It appears thatthe che
mical nature of the capsule prevents the phagocytic cell from adheringto the ba
cterium.Streptococcus contains a heatandacidresistant protein calledM pro
tein,which helps the bacterium resist phagocytosis by white bloodcells.Sallmonella typhi carries a surface antigen,the Vi antigen,thoug
ht to enhance virulence.
Some bacteria have the ability to survive and multiply inside phagocyticcells.A
classic example isMycobacterium tuberculosis,whose sur
viva
l seems to depend on the structure and composition of its cell surface.〖〗
engulf:吞食
Sallmonella typhi:傷寒桿菌
Mycobacterium tuberculosis:結(jié)核桿菌
2.Enzymes
The virulence of some bacteria is thought to be aided by the productionof extra
cellular enzymes and related substances.These chemicals promotespreading of bac
teria in tissues by dissolving hyaluronic acid between cells(Hyaluronidase), ca
use localization of bacteria in tissue by forming blood clot whichprevents host
cells from attacking(Coagulases),dissolve blood clots (Streptokinase) and degr
ade DNA (DNAases).〖〗
hyaluronidase:透明質(zhì)酸酶
coagulases:血漿凝固酶
streptokinase:鏈激酶
3.Antigenic variation
Microbes avoid host immune responses by varying surface antigens.Nei
sseria genorrhoeae express several different PⅡ proteins at any giv
en time,thereby preventi
ng the host from making “speciesspecific”PⅡ protein antibodies.
4.IgA proteases
Neisseria genorrhoeae and H.influenza produc
e enzymes which are capable of cleav
ing secretary IgA antibodies,which presumably enhances the ability of anbacteri
um to survive.
How Pathogens Damage To Host Cells
The ways in which pathogens bring about damage to the host arediverse.Only rare
ly are symptoms of a disease due to the presence of large numbers ofmicroorgani
sms per se.Pathogenic bacteria cause damage to host cells in three basicways:
〖〗
per se：本身
1.by causing direct damage in the immediate vicinity of the invasion;
2.by producing toxins,poisonous substances transported by blood and ly
mph that damage sites far removed from the original site of invasion;
3.by inducing hypersensitivity reaction.〖〗
toxin:毒素
hypersensitivity reaction:變態(tài)反應(yīng)
Most damage by bacteria is done by toxin.Toxins may be almost entirelyresponsib
le for the pathogenic properties of the bacteria.Toxins are of twotypes:EXOTOXI
N and ENDOTOXINS.〖〗
exotoxin:外毒素
endotoxin:內(nèi)毒素
1.Exotoxin
Some bacteria produce exotoxins as part of their growth and metabolismand relea
se the exotoxins into the surrounding medium.Most bacteria that produceexotoxin
s
are grampositive.Exotoxinsare proteins.Most exotoxins consist of two moietie
s:one aids entrance of the exotoxin into the host cells,and the otherprovides t
h
e toxic activity.Because they are soluble in body fluids,exotoxinseasily diff
use into the blood and are rapidly transported throughout the body.〖〗
moiety:單體
Exotoxins work by destroying particular parts of the host′s cells or byinhibit
ing certain metabolic functions.Exotoxin can be grouped into severalcategorie
s based on their biologic effect on host cells.Neurotoxins are bestexemplified
by the botulinum toxin formed by C.botulinum.This potent neurotoxin actson moto
r neurons by preventing the releases of acetylcholine at the myoneuraljuncting,
thereby preventing muscle excitation and producing flaccidparalysis.Diphtheria
is one of cytotoxins which inhibits protein synthesis in many celltypes.Enterot
oxin stimulate hypersecretion of water and electrolytes from theintestinal epit
helium and thus produce watery diarrhera.〖〗
Neurotoxin:神經(jīng)毒素
C.botulinum:肉毒桿菌
acetylcholine:乙酰膽堿
flaccid paralysis:痙攣
Diphtheria:白喉毒素
cytotoxin:細(xì)胞毒素
enterotoxin:腸毒素
electrolyte：電解質(zhì)
Exotoxins are among the most lethal substances known,and 1 mg ofbotulinum toxin
is enough to kill 1 millionguineapigs.For example,tetanus caused by the toxi
n of Glostridium tetani killed as many as 50,000 soldier
s of the Axis powers in
world Ⅱ;the Allied forces,however,immunized soldiers against tetanus,andvery f
ew of their soldiers died of this disease.Fortunately,only a fewbacteria produc
e exotoxins.〖〗
C.tetani:破傷風(fēng)桿菌
The body produces antibodies called antitoxins that provide immunity toexotoxin
s.The antitoxins can react with the exotoxin and neutralize it,whereasantibody
to endotoxin reacts with the LPS complex but has little effect on thebiologic a
ctivity of the complex,except under special conditions.〖〗
antitoxin:抗毒素
When exotoxins are inactivated by heat or formaldehyde,they no longercause the
disease but are still able to stimulate the body to produceantitoxins.Such alte
red exotoxins are called toxoids.When toxoids are injected into thebody,they st
imulate antitoxin production so that immunity is produced to diseases.〖〗
toxoid:類毒素
2.Endotoxin
Endotoxins differ from exotoxins in several ways.Endotoxins are part ofthe oute
r
portion of the cell wall of most gramnegative bacteria.The gramnegativebact
eria have an out membrane surrounding the peptidoglycan layer of thecell wall.T
his out membrane consists of lipoproteins,phospholipids andlipopolysaccharides
(LPS). The lipid portion of LPS,called lipid A,conferstoxicity.Thus,endotoxins
are LPS,whereas exotoxins are proteins.Endotoxins exert their effectswhen the g
ramnegative bacteria die and their cell walls undergo lysis,thusliberating th
e endotoxin.
All endotoxins produce the same signs and symptoms,regardless of thespecies of
microorganism,although not to the same degree.Fever is an almostuniversal sympt
om of endotoxemia,because endotoxin stimulates host cells to releaseproteins ca
lled pyrogens,which affect the temperaturecenter of the brain.Largedose of en
dotoxin can cause death.Thus,endotoxin must be removed from all medicalsupplies
destined for injection onuse during surgical procedures.〖〗
pyrogens:熱原質(zhì)
(龍北國)
英 語 專 業(yè) 詞 匯 表
abortive infection頓挫感染
Viral infection in which viruses enter in a cell but are unable toexpress all t
heir genes to make infectious progeny.
adherence粘附
The attachment of a microorganism to a host cell surface.
aerobes需氧菌
Organisms that use oxygen,including some that must have oxygen.
agar plate瓊脂平板
A plate of medium solidified with agar,a polysaccharide extracted fromcertain m
arine algae.
anaerobes厭氧菌
Organisms that do not use oxygen,including some that are killed byexposure.
antibiotic 抗生素
A chemical substance produced by microorganisms that can inhibit thegrowth of o
r destroy other microorganisms.
antimicrobial agent抗微生物劑
A chemotherapeutic agent used to treat diseases caused by microbes.
antisepsis防腐
A chemical agent that can be safely used externally on tissues todestroy microo
rganisms or to inhibit their growth.
antitoxin抗毒素
An antibody against a specific toxin.
antiviral protein抗病毒蛋白
Protein that interferes with the replication of viruses.
aseptic techniques無菌操作
Techniques used to minimize chances that cultures will be contaminated byorgani
sms from the environment.
bacillus (復(fù)數(shù):bacilli)桿菌
A rodlike bacterium.
bacteremia菌血癥
An infection in which bacteria are transported in the blood but do notmultiply
in transit.
bacterium(復(fù)數(shù)：bacteria)細(xì)菌
bacteriocin細(xì)菌素
Proteins released by some bacteria that inhibit the growth of otherstrains of t
he same or closely related species.
bacteriophage噬菌體
A virus that infects bacteria.
binary fission二分裂
Process in which a bacterial cell duplicates its components and dividesinto two
cells.
blood agar血平板
Type of medium containing sheep blood,used to identify organisms thatcause hemo
lysis,or breakdown of red blood cells.
capsid衣殼、核殼
The protein coating of a virus,which protects the nucleic acid core fromthe env
ironment and determines the shape of the virus.
capsule莢膜
A protective structure outside the cell wall,secreted by the organism.
cell wall細(xì)胞壁
Outer layer of most bacterial,algal,fungal,and plant cells thatmaintains the sh
ape of the cell.
chemotherapy化學(xué)療法
The use of chemical substances to treat various aspects of disease.
chlamydia衣原體
Tiny,nonmotile,spherical bacterial; all are obligate intracellularparasites wit
h a complex life cycle.
chronic infection慢性感染
coagulase血漿凝固酶
Bacterially produced enzyme that accelerates the coagulation of blood.
coccus(復(fù)數(shù)：cocci)球菌
A spherical bacterium.
colonization定植
Growth of microorganisms on epithelial surfaces such as skin or mucousmembranes
.
colony菌落
A group of descendants of an original cell.
conjugation接合
Transfer of genetic information from one bacterial cell to another bymeans of p
ili.
contagious disease傳染病
Infectious disease that can be spread from one host to another.
culture培養(yǎng)，培養(yǎng)物
cytotoxin細(xì)胞毒素
An kind of exotoxin produced by bacteria.
decline phase衰亡期
The fourth of four major phases of the bacterial growth curve in whichcells los
e their ability to divide (due to less supportive conditions in themedium) and
thus die.
disinfectant消毒劑
A chemical agent used on inanimate objects to destroy microorganisms.
disinfection消毒
Reducing the number of pathogenic organisms on objects or in materialsso that t
hey pose no threat of disease.
endospore 芽胞
A resistant,dormant structure,formed inside some bacteria such asBacillus and C
lostridium,that can survive adverse conditions.
endogenous infection內(nèi)源性感染
An infection caused by microorganisms that exist in the body.
endotoxin內(nèi)毒素
A toxin incorporated in gramnegative bacterial cell walls and releasedwhen th
e bacterium dies.
enterotoxin腸毒素
An exotoxin that acts on tissues of the gut.
envelope包膜
A bilayer membrane found outside the capsid of some viruses, acquired asthe vir
us buds through the host cell′s membrane.
exogenous infection外源性感染
An infection caused by microorganisms that enter the body from the environment.
exotoxin外毒素
A soluble toxin secreted by microbes into their surroundings,includinghost tiss
ues.
exponential growth對(duì)數(shù)生長期
Growth of a bacterial culture characterized by doubling of thepopulation in a f
ixed interval of time.
facultative anaerobee兼性厭氧菌
Bacteria that carry on aerobic metabolism when oxygen is present butshift to an
aerobic metabolism when oxygen is absent.
fermentation發(fā)酵
Anaerobic metabolism of the pyruvate produced in glycolysis.
flagellum (復(fù)數(shù)：flagella)鞭毛
Long,thin,helical appendages of certain cells that provide means oflocomotion.
flora disequilibrium菌群失調(diào)
fungus(復(fù)數(shù)：fungi)真菌
Nonphotosynthetic,eukaryotic organisms that absorb mutrients from theirenvironm
ent.
germ病原微生物(菌)
Pathogenic microorganisms.
Gram stain革蘭氏染色法
A differential stain.Grampositive bacteria stain dark purple,gramnegativeon
es stain pink/red.
growth curve生長曲線
The different growth periods of a baterial or phage population.
hepatitis肝炎
An inflammation of the liver,usually caused by viruses but sometimes byan amoe
ba or various toxic chemicals.
helper virus.輔助病毒
horizontal transmission水平傳播
host寄主
Any organism that harbors another organism.
hypha(復(fù)數(shù)：hyphae)菌絲
Long,threadlike structures of cells in fungi or actinomycetes.
infection感染
The multiplication of a parasite,usually microscopic,within the body.
inoculation接種
interferon干擾素
A small protein released from virusinfected cells which binds adjacentcells,c
ausing them to produce a protein that interferes with viral replication.
invasiveness侵襲力
The ability of a microorganism to take up residence in a host.
L formsL型細(xì)菌
Irregularly shaped naturally occurring bacteria with defective cellwalls.
lag phase遲緩期
First of four major phases of the bacterial growth curve,in whichorganisms grow
in size but do not increasein number.
latent infection潛伏感染
lipid脂質(zhì)A、類脂A
Toxic substance found in the cell wall of gramnegative bacteria.
lipopolysaccharide(LPS)脂多糖
Part of the outer layer of the cell wall in gramnegative bacteria.
logarithmic phase對(duì)數(shù)期
Second of four major phases of the bacterial growth curve,in which cellsdivide
at an exponential or logarithmic rate.
lysozyme溶菌酶
An enzyme that acts on polysaccharides to weaken the bacterial cellwalls.
medium(復(fù)數(shù)：media)培養(yǎng)基
microaerophilic bacteria微需氧菌
Bacteria that grow best in the presence of a small amount of freeoxygen.
microbe微生物
microorganism微生物
microscope顯微鏡
microbiology微生物學(xué)
The study of microorganisms.
mycoplasmas支原體
Very small bacteria with cell membranes,RNA and DNA,but no cell walls.
neurotoxin神經(jīng)毒素
A toxin that acts on nervous system tissues.
normal flora 正常菌群
Microorganisms commonly found in or on another organism.
nosocomial infection 醫(yī)院內(nèi)感染
An infection acquired in a hospital or other medical facility.
nucleoid擬核
Nuclear region in bacteria.
nucleocapsid核衣殼
obligate aerobe專性需氧菌
Bacteria that must have free oxygen to grow.
obligate anaerobe專性厭氧菌
Bacteria that are killed by free oxygen.
opportunistic bacterium機(jī)會(huì)致病菌
Species of resident of transient flora that do not ordinarily causedisease but
can do so under certain conditions.
outer membrane外膜
A bilayer membrane,surrounding the cell wall of gramnegative bacteria.
pasteurization巴斯德消毒法
Mild heating to destroy pathogens and other organisms that causespoilage.
pathogen病原體
Any parasite capable of causing disease in its host.
pathogenic bacterium病原菌
pathogenicity致病性
The capacity to produce disease.
penicillin青霉素
An antimicrobial agent made by the mold Penicillium.
peptidoglycan肽聚糖
A structural polymer in the bacterial cell wall that forms a supportingnet.
peptone蛋白胨
A product of enzyme digestion of proteins that contains many small peptides;a c
ommon ingredient of a complex medium.
persistent infection持續(xù)感染
phage See bacteriophage噬菌體
phagocytosis吞噬作用
Digestion of solids into cells by means of the formation of vacuoles.
pigment色素
pilus(復(fù)數(shù)：pili)菌毛
Tiny hollow projections used to attach bacteria to surfaces (fimbriae)of for co
njugation( sex pili).
plasmid質(zhì)粒
A small circular piece of DNA in a cell that is not part of itschromosome.
plate平板
prion類病毒
An exceedingly small infectious particle alleged to consist of proteinwithout a
ny nucleic acid; their existence has been challenged by someinvestigators.
prophage前噬菌體
Phage DNA that has entered a bacterium.
protoza立克次體
Singlecelled,microscopic,eukaryotic organisms in kingdom Protista.
pure culture純培養(yǎng)
A culture that contains only a single species of organism.
pyemia膿毒血癥
pyrogen熱原質(zhì)
A substance that acts on the hypothalamus to raise the body′s “thermostat” to
a higherthannormaltemperature.
R factors (plasmids)R因子、R質(zhì)粒
Drug resistance plasmids,which carry genes that provide resistance tovarious an
tibiotics.
replication復(fù)制
Process by which an organism of structure (especially a DNA molecule)duplicates
itself.
reproduce繁殖
reservoir of infection傳染源
Sites where microorganisms can persist and transmission to other hosts.
resident flora常居菌群
Species of microorganisms that are always present on or in an organism.
resistance耐藥性
The ability of a microorganism to remain unharmed by an antimicrobialagent.
resistance transfer factor 耐藥性傳遞因子
Component of a resistance plasmid that implements transfer by conjugationof the
plasmid.
rickettsia立克次體
Small,nonmotile,gramnegative organisms;obligate intracellular parasitesof ma
mmalian and arthropod cells.
septicemia敗血癥
An infection caused by rapid multiplication of pathogens in theblood;formerly c
alled blood poisoning.
slow viral infection慢(發(fā))病毒感染
smear涂片
A thin layer of liquid specimen spread out on a microscope slide.
spirillum(復(fù)數(shù)：spirilli)螺菌
A corkscrewshaped bacterium
spike刺突
spirochete螺旋體
A flexible,wavyshaped bacterium.
spore孢子
A resistance reproductive structure formed by fungi andactinomycetes;different
from bacterial endospores.
stain染色
A molecule that can bind to a structure and give it color.
staphylococcus aureus金黃色葡萄球菌
staphylococcus epidermidis表皮葡萄球菌
stationary phase穩(wěn)定期
The third of four major phases of the bacterial growth curve in whichnew cells
are produced at the same rate that old cells die,leaving the number oflive cell
s constant.
sterility無菌
The state in which there are no living organisms in or on a material.
sterilization滅菌
The killing or removal of all microorganisms in a material or on anobject.
strain菌株
A subgroup of a species with one or more characteristics thatdistinguish it fro
m other subgroups that species.
streak plate method平板劃線分離法
Method used to prepare pure cultures in which bacteria are lightlyspread over t
he surface of agar plates,resulting in isolated colonies.
superinfection二重感染
Invasion of digestive,respiratory,or urinary tracts by resistancereplacement fl
ora when normal flora are disturbed.
temperate phage溫和噬菌體
A phage that ordinarily does not cause a virulent infection but ratheris incorp
orated into a bacterium and replicated with it.
toxemia毒血癥
The presence of pathogenreleased toxins in the blood.
toxin毒素
A poisonous substance.
toxoid類毒素
An exotoxin inactivated by chemical treatment which retains itsantigenicity and
therefore can be used tovaccinate against the toxin.
transduction轉(zhuǎn)導(dǎo)
The transfer of genetic material from one bacterium to another by abacteriophag
e.
transformation轉(zhuǎn)化
A change in an organism′s characteristics through the transfer of nakedDNA.
transient flora過路菌群
Microorganisms that may be present in or on an organism under certainconditions
and for certain lengths oftime.
transposon轉(zhuǎn)座子
vaccine疫苗
A substance that contains an antigen to which the immune systemresponds.
vegetative form繁殖體
Cells that are actively metabolizing nutrients.
vertical transmission垂直傳播
Direct contact transmission of disease in which pathogens are passedfrom parent
to offspring in an egg orsperm,across the placenta,or while traversing the bir
th canal.
vibrio弧菌
A commashaped bacterium.
viremia病毒血癥
An infection in which viruses are transported in the blood but do notmultiply i
n transit.
virion病毒顆粒
A complete virus particle,including its envelop if it has one.
virology病毒學(xué)
The study of viruses.
virulence毒力
The degree of intensity of the disease produced by a pathogen.
virulent phage 烈性或毒性噬菌體
A phage that enters the lytic cycle when it infects a cell,causingeventual deat
h of the cell.
virus病毒
Submicroscopic,parasitic,acellular entities composed of a nucleic acidcore insi
de a protein coat.
yeast酵母菌
(龍北國)
