Topley and Wilson's Microbiology and Microbial Infections, 8 Volume Set

6289 Pages·2010·123.19 MB·English

by  Topley

The bacteria: historical introduction
BOHUMIL S. DRASAR
History 1 Nonmedicalapplicationsofbacteriology 7
Microbiology 1 Thetwentiethcentury 8
Communicablediseases 2 Systematicbacteriology 8
The‘germtheory’ 2 Acknowledgments 12
Fermentationandputrefaction 2 References 12
Pathogenicmicroorganisms 3
HISTORY concerns the organisms themselves and ‘applied’ micro-
biology their effects on other living beings, when they
The problem with writing about history is that develop- act as pathogens or commensals, or on their inanimate
ments appear inevitable and indeed when we present a environment,whentheybringaboutchemicalchangesin
chronological account this must be the case. However, it. Thus, microbiology has applications in human and
it is as well to remember that at each point in the story veterinary medicine, in agriculture and animal
the outcome could have been different. The advances husbandry, and in industrial technology and even clima-
in medicine in the twentieth and twenty-first centuries tology.
are the result of the demonstration of the validity of Microorganisms were first seen and described by the
the germ theory in the nineteenth century and most Dutch lens-maker Antonie van Leeuwenhoek (1632–
significantly the establishment of its functional utility. 1723),whodevisedsimplemicroscopescapableofgiving
It is easy to forget how recent these advances are. magnifications of c. (cid:1)200. In a number of letters to the
In 1922, Topley succeeded Sheridan Dele´pine in Royal Society of London between 1673 and his death,
the Bacteriology Department of the University of he gave clear and accurate descriptions and drawings of
Manchester. Dele´pine had worked with Pasteur. This a variety of living things that undoubtedly included
was a world before molecular biology, before most protozoa, yeasts, and bacteria (Dobell 1932). These
immunology, and at the beginnings of antimicrobial striking observations did not lead immediately to great
chemotherapy. Here, some of the advances are docu- advances in the knowledge of microbes. These were
mented, but the choice of what to include is deter- delayedfornearlytwocenturies,untilessentialtechnical
mined by the concerns of the present and the recent advances had been made by workers who nowadays
past and may not reflect fully the concerns and would be described as industrial or medical micro-
priorities of the past. biologists.
When bacteriology started in the nineteenth century
MICROBIOLOGY the borders of the discipline were uncharted and much
of what would now be called virology and immunology
Microbiology is the study of living organisms (‘micro- was included. More recently bacteriology has contrib-
organisms’ or ‘microbes’), simple in structure, and utedto,orperhapsbeensubsumedby,theemergenceof
usually small in size, that are generally considered to be molecular biology. Such categories are largely arbitrary
neither plants nor animals; they include bacteria, algae, and the concern here is to present an outline that does
fungi, protozoa, and viruses. ‘Pure’ microbiology justicetotherootsofthesubject.
2 Thebacteria:historicalintroduction
COMMUNICABLE DISEASES significance was not fully realized until the germ theory
was accepted. As late as 1894 Creighton, in his still
Long before microbes had been seen, observations on unsurpassed ‘History of Epidemics in Britain,’ based his
communicable diseases had given rise to the concept of understandingonthemiasmatictheory.
contagion: the spread of disease by contact, direct or Theintellectualandscientificcaseforthegermtheory
indirect. This idea was implicit in the laws enacted in was established by the studies of Koch and Pasteur,
early biblical times to prevent the spread of leprosy. It which are set out below, but there was no immediate
became less influential in the classical era, when super- widespread acceptance. The Hamburg cholera outbreak
natural and miasmatic causes were favored. In the later and the dispute between Koch and Pettenkoffer both
Middle Ages, there was renewed interest in contagion, publicized and showed the strength of the theory.
reinforced at the end of the fifteenth century by the Drinking water from Hamburgwas taken from the river
spread of syphilis in Europe, which was obviously asso- Elbeabovethetownandsewagewasdischargedintothe
ciated with a specific form of contact. Fracastorius river. In Hamburg there were many cases of cholera.
(GirolamoFracastoro),aphysicianofVerona,published Altona, downstream from Hamburg, also drew drinking
aninfluentialanalysisofcontagionin1546: waterformtheElbe;however,thiswaterpassedthrough
slow sand filters before distribution. In Altona there
. byphysicalcontactalone
were only a few cases of cholera. The demonstration
. byformites,and
that removal of contamination from the water supplies
. atadistance.
prevented infection convinced the public and the
He was led to conclude that communicable diseases medical profession of the bacterial etiology of the
werecausedbylivingagents;thesehespokeofas‘semi- disease. In spite of this elegant demonstration of
naria’ or ‘seeds,’ but he was unable to give a more defi- the waterborne transmission of Vibrio cholerae and the
niteopinionabouttheirnature. mechanism for control, not all were convinced. Petten-
In the subsequent 250 years, several authors specu- koffer and Emmerich both drank 1ml of V. cholerae
lated that the agents of contagious diseases were culture. Both survived (Pettenkoffer 1892). This publi-
animate, but little evidence for this was produced. Even cityundoubtedlyhelpedtopopularizethetheory.
therecognitionofparasitism ofanimals,e.g.scabiesand
some forms of helminthiasis (see Foster 1965), appears FERMENTATION AND PUTREFACTION
to have had little impact on thinking about the role of
microorganisms as pathogens. Early in the nineteenth
In the first half of the nineteenth century, chemists
century, improvements had been made in the design of
became interested in fermentation: industrial processes
microscopes and between 1834 and 1850 numerous
in which organic substances underwent changes that
accounts were published of morphologically recogniz-
yielded useful compounds, such as alcohol and acetic
able microorganisms in material from diseased animals
acid. A similar process, termed putrefaction, led to the
or human subjects: of fungi subsequently called Botrytis
decay of organic matter, usually with the production of
in the silkworm disease ‘calcino’ by Bassi; of trichomo-
an unpleasant odor and taste. In the 1830s, several
nads in human vaginal discharges by Donn(cid:1)ee; of ring-
observers, notably Cagniard-Latour and Schwann, saw
worm fungi by Scho¨nlein and by Groby; of vibrios in
yeasts in liquors undergoing alcoholic fermentation and
cholera stools by Pouchet; and of large rod-shaped
concluded that these were living organisms and the
bacteria in anthrax blood by Rayer and Davaine (for
cause of the process. This view was resisted by leading
referencesseeBulloch1938).
authorities of the day (Berzelius, Liebig, Wohler), who
considered that fermentation was a purely chemical
THE ‘GERM THEORY’
process and that the yeasts were a consequence rather
thanthecauseofit.Between1836and1860controversy
In 1840, Henle affirmed his belief in what came to be
ragedbutwithoutaclearoutcome.
called the ‘germ theory of disease,’ which asserted that
certain diseases were caused by the multiplication of
The work of Louis Pasteur
microorganisms in the body, but he advanced little
supporting evidence for this and his view was hotly
disputed. Louis Pasteur (1822–1895) (Figure 1) produced strong
The lack of a germ theory probably led to the initial experimental evidence that microorganisms were the
rejection by the General Board of Health in 1854 of cause of fermentation and in so doing laid the founda-
Snow’s explanation of the waterborne spread of cholera tions of microbiology as a science. He was a chemist
in London. In groundbreaking investigations, Snow whose early studies of fermentation aroused his interest
established that cholera was spread by water contami- in the molecular asymmetry of some of the compounds
nated with human feces; however, these findings formed. He concluded that optically active chemical
conflicted with the miasmatic theory and their compounds, such as the stereoisomeric forms of tartaric
Pathogenicmicroorganisms 3
and demonstrated numerous sources of contamination
from air, dust, and water. He showed that some organ-
isms were not destroyed by boiling. For the sterilization
of fluids, he advocated heating to 120(cid:2)C under pressure,
and for glassware, the use of dry heat at 170(cid:2)C; he
showed the value of the cottonwool plug for protecting
materialfromaerialrecontamination.
In the course of these experiments Pasteur used
various forms of nutrient fluid to grow microorganisms
and showed that a medium suitable for one might be
unsuitable for another, so for successful cultivation it
wasnecessarytodiscoverasuitablegrowthmediumand
toestablishoptimalconditionsoftemperature,acidityor
alkalinity,andoxygentension.
The mass of experimental data produced by Pasteur
carried general conviction, but a minority of adherents
of heterogenesis continued to maintain their position,
often supporting this by experiments in which inade-
quate heating had failed to destroy very heat resistant
bacteria. The observations of Tyndall in the early 1870s,
that all actively multiplying bacteria were easily
destroyedbyboiling,ledtotheintroductionofamethod
ofsterilizationbyrepeatedcyclesofheatinginterspersed
with periods of incubation. This method of ‘tyndalliza-
tion’servedtoeliminatemanyoftheanomaliesreported
bytheadvocatesofheterogenesis(seeBulloch1938).
Pasteur devoted much effort to investigating the trou-
bles of French winemakers, brewers, and vinegar
makers. These studies often led him to perform experi-
Figure1LouisPasteur(1822–1895).
ments of fundamental scientific importance, as when his
involvement in the problems of vinegar making led to
acid and amyl alcohol, never arose from the purely valuable observations on the constancy of microbial
chemicaldecomposition ofsugarsbutwereformedfrom characters in culture. His general conclusion was that
them by the action of microorganisms; these were fermentations owed their diversity to the characters of
always present in fermenting liquors and increased in the several organisms responsible for them, but final
numberastheprocesscontinued.Differentfermentation proof of this was not obtainable until methods of
processes(e.g. alcoholic,acetic, butyric) were eachasso- obtainingpurecultureshadbeendiscovered.
ciated with particular organisms, which were often
recognizable by their morphology or requirements for PATHOGENIC MICROORGANISMS
growth.
To maintain that microorganisms caused fermenta- In about 1865, Pasteur responded to an appeal to inves-
tion, it was necessary to establish that they did not arise tigate a formidable disease of silkworms in southern
de novo. This was contrary to the widely held belief in France (p(cid:1)eebrine); by 1869, his experiments had led him
the spontaneous generation of living things from dead to the conclusion that this was a communicable disease
animal or vegetable material (‘heterogenesis’). Contro- transmitted by direct contact or fecal contamination.
versy about this in the eighteenth century had centered This, according to his biographer Vallery-Radot (1919),
around the conditions under which putrefaction devel- engendered in his mind the idea that communicable
oped in organic matter that had been subjected to diseases of animals and man, like the ‘diseases’ of wine
supposedly sterilizing temperatures in closed containers. and beer, might be a consequence of microbial multi-
Thismatterwasunresolvedin1860.Inaseriesofadmir- plication.
able experiments reported in the next 4 years (see From1857onwardtherehadbeenreports,notablyby
Vallery-Radot 1922–33), Pasteur disposed of many Brauell and Davaine, of the transmission of anthrax
purported instances of heterogenesis by showing that between animals by the injection of blood. At that time
they couldbe attributed to failure ofthe initial steriliza- there was also much interest in the septic and pyemic
tion or to subsequent recontamination. He emphasized diseases of man, including ‘surgical fever’ (see Bulloch
the need for scrupulous sterilization of everything 1938). In 1865, Coze and Felty began to publish a series
comingintocontactwiththematerialunderexamination ofpapersreportingthepresenceofbacteriaintheblood
4 Thebacteria:historicalintroduction
ofdogs and rabbits that had received injections ofpuru- bacillus in experimental animals, of its growth in vitro,
lent material from human patients. In 1872, Davaine, and of theformation and germination of its spores. This
starting with blood from patients suffering from ‘putrid’ opened up a new era in bacteriology. In the following
infections, performed serial passage in experimental year, he described the fixing and staining of bacteria
animalsanddemonstratedenhancementofvirulence. with the newly introduced aniline dyes. In 1878, his
Joseph Lister (1827–1912) was aware of Pasteur’s study of wound infections explored the role of animal
demonstration that both fermentation and putrefaction experimentation in establishing the cause of bacterial
might be initiated by airborne organisms. On the infections. Then, in 1881, he described means of culti-
assumption that ‘putrefying’ wounds might be similarly vatingbacteriaonsolidmedia,thusmakingitpossibleto
caused, he attempted to prevent surgical sepsis by obtain pure cultures by transferring material from a
denyingaccesstowoundsofmicrobesfromthepatient’s single colony. First he used pieces of potato as his
surroundings, particularly from the air. His ‘antiseptic’ growth medium, thennutrient gelatin, and lateragargel
regimen,firstdescribedin1867,wasstrikinglysuccessful media. In 1882 and 1884, he published classic papers on
and transformed the prognosis of major surgical opera- the tubercle bacillus, and in 1883, he described the
tions. Lister did not prove that this was due to the choleravibrio.
destruction of potentially pathogenic microbes, but this Koch had now assembled the techniques needed to
wasrenderedhighlyprobablebythecontemporarywork investigate the bacterial causes of many communicable
ofFrenchandGermanbacteriologists. diseases. He had moved to Berlin, where Loeffler and
Inretrospect,theworkofanothersurgeon,Alexander Gaffky were already his assistants; later came Pfeiffer,
Ogston(1844–1929),whodescribedstaphylococciinpus, Kitasato,Welch,andmanyothers.Kochbegantogather
assumes perhaps equal importance and helped lay the round him the group of followers who were destined to
foundations for the study of hospital infection. The introduce his methods into many laboratories
history of hospital infection was reviewed by Selwyn throughouttheworld.
(1991)andAyliffeandEnglish(2003). We should remember that not allthe techniqueswere
devised by Koch; agar was first used by Hesse at the
The work of Robert Koch suggestion of his wife Fannie. In 1887, Petri described
his culture dish, which remains a mainstay of bacter-
iologicalisolation.
In 1876, while a country physician at Wollstein in
The fruits of this technical revolution appeared with
easternGermany,RobertKoch(1843–1910)(Figure2)
remarkable speed during the years 1876–90, the period
published his first scientific work, a study of the anthrax
described by Bulloch (1938) as ‘the heyday of bacterial
etiological discovery,’ when most of the important
groups of bacterial pathogensfor manand animalswere
recognized.
Differential staining
In 1878, Paul Ehrlich had noted differences in the affi-
nity for aniline dyes of various types of living cells, an
observation that started him on his long search for
chemotherapeutic agents. In 1882, he reported that
tubercle bacilli stained with fuchsin retained the dye
when subsequently treated with a mineral acid; this
property of ‘acid-fastness’ formed the basis for methods
laterdevelopedtodetectmycobacteriaintissuesections,
insputumandothersecretions,andincultures.
A differential staining method of even wider applic-
ability arose from the observation, reported in 1884 by
theyoungDanishphysicianChristianGram,thatcertain
bacteria, when stained with methyl violet and treated
withaniodinesolution asamordant, retainedtheviolet
dye when washed briefly with ethyl alcohol. The ‘gram
reaction’ proved to be a useful means of dividing
bacteria into two categories: ‘gram-positive’ organisms
that were stained violet and ‘gram-negative’ organisms
Figure2RobertKoch(1843–1910). that lost the violet dye and were stained red by a
Pathogenicmicroorganisms 5
counterstain applied after washing with alcohol. This with a live vaccine against the pasteurella of chicken
property was later found to reflect differences in cell- choleraand in1881withoneagainstanthraxinanimals.
wall composition and to be correlated with a number of In 1886, Pasteur reported on the use of an attenuated
othercharacters; organisms that retained thevioletstain live vaccine against rabies. This consisted of a dried
were in general less susceptible, than those that did suspensionofspinalcordfromaninfectedrabbit.Itsuse
not, to various chemical substances and to lysis by was an extension of the original principle of vaccination
complementinthepresenceofspecificantibody. in that the material was given after infection had taken
place. It was used with apparent success to prevent
Establishing the pathogenicity of disease in human subjects who had been bitten by a
bacteria rabid animal. Most of the early attenuated living
vaccines caused appreciable morbidity and even some
deaths, but in 1886, Salmon and Smith showed that it
As the number of different bacteria found in constant
was possible to protect pigeons against salmonella infec-
association with human and animal diseases grew, the
tion by the injection of heat-killed organisms. Pfeiffer
question of how to establish their etiological role
demonstrated in 1889 that immunity conferred by vacci-
assumed importance. Already in the 1880s it was being
nation was usually highly specific, but there were excep-
recognized that, though the internal organs were
tionstothis.
normally sterile or nearly so, many surface sites and
At a somewhat earlier date, Metchnikoff had
body cavities communicating with the outside had a
observed the engulfment of bacteria and other microbes
rich bacterial flora, so the presence of an organism
by phagocytes; in 1891, he expressed the view that
here was of little significance. When inflammatory
immunity was primarily cellular. This conflicted with
lesions appeared in such places it was often difficult to
growing evidence for the importance of serum factors;
decide which, if any, of the organisms present was
thealternativehumoralviewofimmunitywasthat‘anti-
responsible.
bodies’ appeared in the serum of vaccinated or infected
Koch’s experience with anthrax, wound infection, and
animalsandthattheirspecificitycorrespondedtothatof
tuberculosis led him to place much reliance on the
the‘antigens’thatelicitedthem.
evidence of animal experimentation in establishing rela-
Strong evidence for humoral immunity emerged after
tionships between disease and isolate. A set of condi-
Roux and Yersin in Paris had demonstrated in 1888
tions, all of which must be fulfilled to justify such a
the characteristic lethal effects of broth cultures of
conclusion, has been called Koch’s postulates. They are
diphtheria bacilli on guinea-pigs and shown that these
as follows (see Topley and Wilson 1931), though Koch
were caused by the liberation of a soluble toxin, an
didnotstatetheminpreciselythisform:
‘exotoxin.’ In the following year, Behring in Koch’s
. the organism is regularly found in the lesions of the laboratory observed that chemically sterilized broth
disease cultures of diphtheria bacilli retained their toxicity for
. it can be grown in pure culture outside the body of guinea-pigs but animals given sublethal doses of them
thehostforseveralgenerations,and were subsequently immune to diphtheria. He also
. such a culture will reproduce the disease in question showed that the pleural fluid of animals dead of diph-
when administered to a susceptible experimental theria was toxic but yielded no diphtheria bacilli on
animal. culture; however, injections of it rendered other
guinea-pigs immune. By 1890, Behring had demon-
Itsubsequentlyproveddifficultorimpossibletofulfillall
strated that the blood of immunized guinea-pigs
thesecriteriainrespectofmanymicrobialdiseases.
neutralized diphtheria toxin in vitro. Faber demon-
strated tetanus toxin in 1889; the following year,
Immunity
Behring and Kitasato immunized rabbits against it and
showed that their serum protected mice against
Folk medicine had long established that exposure to tetanus.
certain infective agents might engender immunity to By 1890, many of the basic areas of immunology had
them (Parker 1998) and experience with Jennerian been outlined, though some concepts that are now
vaccination against smallpox had indicated the value of considered as basic were discovered surprisingly late.
selecting astrain ofthe agent with low virulence for use The secondary response was described by Glenny and
as an inducer of immunity. While Koch and his pupils Sudmerson (1921) and the concept of herd immunity by
were continuing to characterize more and more patho- Topleyand Wilson(1923). Theseeventsset thestudyof
gens, Pasteur turned his attention to the possibility of immunityonafirmfoundationandformthebasisofthe
inducing prophylactic immunity by injections of live discipline of immunology; the further history can be
cultures of organisms, the virulence of which had been foundintheImmunologyvolume History.
attenuated by prolonged culture or by growth under The chronology of these events is summarized in
suboptimal conditions. Success was reported in 1877 Tables 1 and 2. Figure 3 shows the Bacteriological
6 Thebacteria:historicalintroduction
Table1Bacteriologyinthenineteenthcentury
Year Event
1834–50 Fungi,protozoa,andbacteriaseenindiseasedtissuesorsecretions(seetext)
1836–37 Yeastsseeninliquorsundergoingalcoholicfermentation
1840 Henle:‘germtheoryofdisease’
1844–57 Pasteur:studiesopticallyactivecompoundsfromfermentedfluids
1849-54 Snow:waterbornetransmissionofcholera
1857–63 Pasteur:reportsthatanthraxistransmittedbyinjectionsofbloodfromdiseasedanimals
1860–64 Pasteur:experimentalevidencethatfermentationandputrefactionareeffectsofmicrobialgrowth
1865–67 Pasteurstudies‘pee(cid:1)brine’ofsilkworms;concludesthatitiscausedbymicrobialaction
1867 Lister:successof‘antisepticsurgery’supportsviewthatmicrobescausepostoperativesepsis
1876 Koch:demonstratespathogenicityandsporulationofanthraxbacilli
1877 Koch:stainingofbacteriabyanilinedyes
1877 Tyndall:heat-resistantbacteriadestroyedbyrepeatedcyclesofmoderateheatingandincubation
1877 Pasteur:chickencholerapreventedbyinjectionsofliveattenuatedculture
1877 Soilnitratesreplenishedbymicrobialaction
1878 Koch:studiesofwoundinfection;useofexperimentsonanimalstoestablishetiology
1879 Ehrlich:differencesinaffinityofchemicalsubstancesforvarioussortsoflivingcells
1880 Ogsten:staphylococciinpus
1881 Koch:useofsolidmediatoobtainpureculturesofbacteria
1881 Pasteur:anthraxpreventedbyliveattenuatedvaccine
1882 Ehrlich:acidfastnessofthetuberclebacillus
1882 Hesse:useofagartosolidifyculturemedia
1882–84 Koch:etiologicalroleofthetuberclebacillus;‘Koch’spostulates’
1883 Kochdescribesthecholeravibrio
1883–91 Metchnikoffstudiescellulardefencemechanisms
1884 Chamberlandfilters
1884 Gram’sstain
1886 Pasteur’srabiesvaccine
1886 SalmonandSmith:killedbacterialvaccineseffective
1887 Petri:double-sidedculturedish
1888 RouxandYersin:diphtheriabacillusformsexotoxin
1888 Nuttall:serumkillingofbacteria
1889 Behring:antitoxicimmunitytodiphtheria
1889 Pfeiffer:specificityofimmunityconferredbyvaccines
1889 Faber:tetanusbacillusformsexotoxin
1889 Buchner:serumkillingofbacteriainhibitedbyheatingtheserum
1890 Behring:diphtheriaantitoxinneutralizestoxininvitro
1890 BehringandKitasato:antitoxicimmunitytotetanus
1890 Winogradsky:nitrite-andnitrate-formingbacteriainsoil
1892 Tobacco-mosaicdiseasetransmittedbyfilteredmaterial
1894 Pfeiffer’sphenomenon:lysisofvibriosinperitonealcavity
1895 Bordet:heat-stableandheat-labilefactors(respectively,antibodyandcomplement)inimmunelysis
1897 Ehrlich:‘side-chaintheory’ofantibodyproduction
1898 Foot-and-mouthdiseasetransmittedbyfilteredmaterial
Section of the Congress of Hygiene and Demography, macromolecules: in 1884, Chamberland introduced
London,1891. filters made of unglazed porcelain and in 1891 Nordt-
meyer introduced the Berkefeld-type of filter
Bacterial filters and the origins of
composed of kieselguhr. There were several important
virology
consequences of these innovations, as follows.
Filtration provided a convenient means of producing
An important technical advance in the latter part of bacteria-free preparations of soluble toxins and thus
the nineteenth century was the development of filters greatly simplified the task of producing reagents for
that held back bacteria but allowed the passage of passive and active immunization against diphtheria and
smaller microorganisms and biologically important tetanus. It was also an essential preliminary to the
Nonmedicalapplicationsofbacteriology 7
Table2Thetwentiethcentury and also led to important developments in bacterial
Year Event genetics(see Bacterialgenetics).
1900 Reed:yellowfevervirus NONMEDICAL APPLICATIONS OF
1911 Rous:chickensarcomacausedbyavirus
BACTERIOLOGY
1912 EhrlichandHata:Salvarsanforthetreatment
ofsyphilis
The discoveries of Pasteur and Koch had important
1915/17 Twortandd’Herrelle:‘bacteriophage’
applications for agriculture and industry. The replace-
1921 GlennyandSudmerson:thesecondary
responsetoantigen ment of nitrates lost from thesoil by the washing action
1923 TopleyandWilson:herdimmunity of rain had long been a mystery but it seemed to be
1928 Griffith:thetransformationofpneumococci connected in some way with the decomposition of
1929 Fleming:penicillin–thefirstantibiotic organicmatter.In1877,SchloesingandMuntz,actingon
1935 Domagk:prontosil–thefirstsuphonamide a suggestion from Pasteur, showed by experiment that
1944 Avery,MacLeod,andMcCarty:DNA the formation of nitrates was due to the action of living
astheagentoftransformation organisms. Warington confirmed this in 1878 and 1879
1944 Schartz,Bugie,andWaksman: and demonstrated that the process took place in two
streptomycin–thefirstantituberculosis
stages: first, the conversion of ammonia to nitrites, and
treatment
then the oxidation of nitrites to nitrates. He believed
1946 LederbergandTatum:conjugationinbacteria
thatthesetwostageswereperformedbydifferentorgan-
1952 LederbergandZinder:phagetransductionof
isms but failed to prove this. In 1890, Winogradsky
bacteria
isolated and described the nitrogen-fixing bacteria that
1953 Crick,Franklin,Watson,andWilkins:structure
ofDNA caused the formation of nodules on the roots of legumi-
1960 Jacob,Perrin,Sanchez,andMonod:theoperon nous plants. Later, Winogradsky described a free-living
concept anaerobic organism that fixed atmospheric nitrogen and
1961 Brenner,Jacob,andMeselson:ribosomes Beijerinck, some 10 years afterwards, described a large
siteofproteinsynthesis free-living nitrogen-fixing aerobe that he named Azoto-
1973 Cohen,Chan,Helling,andBoyer: bacter.
plasmidvectors
Theimportanceofbacteriainmaintainingthefertility
1977 Fox,Pecham,andWoese:molecular
of the soil has thus been recognized for over a century.
systematics(16SRNA)
A more recent concept is that the chemical activities of
1977 Woese:Archaebacteria
primitive ancestral microbial forms may have created
1977 GilbertandSanger:DNAsequencing
the atmospheric conditions essential for the appearance
1986 Mullis:thepolymerasechainreaction(PCR)
ofplantsandanimalsonearth(seeSchlegel1984).
1995 Venter,Smith,andFraser:genomesequence
ofHaemophilusinfluenzae Bacteriacausediseasesofplantsaswellasanimals.In
1878,Burrilldescribedtheorganismresponsibleforpear
blight and, in 1883, Wakker described the bacterial
cause of ‘yellows’ of hyacinths. Recognition of the role
purification of toxins and to chemical studies of their of bacteria in the spoilage of foodstuffs and in the
constitution. productionoforganicchemicalsusefultomanledtothe
It soon became apparent that some disease agents entrance of the bacteriologist into numerous industrial
passed through bacteria-retaining filters; thus, the first fields.
viral pathogens were recognized. In 1892, Iwanowski
described the transmission of mosaic disease to tobacco The development of ‘pure’
plants and, in 1898, Loeffler and Frosch described the bacteriology
transmissionoffoot-and-mouthdiseaseinbovinesbythe
injection of filtrates of infective material. In 1900, Pasteur’s studies of fermentation in the early 1860s
Walter Reed demonstrated that yellow fever is caused revealedthephysiologicaldiversityofmicrobesandmay
by a filterable agent (Reed 1902). The further history of be looked upon as the starting-point of ‘pure’ bacter-
virologyisdealtwithintheVirologyvolume, iological studies. During the 1870s, he became more
Ashorthistoryofresearchonviruses. concerned with the role of microbes as pathogens, but
A later consequence of the use of bacterial filters was he continued to be interested in their basic properties.
the discovery, independently by Twort in 1915 and by For example, in 1878, he described under the name
d’Herelle in 1917, of bacteriophages, subsequently ‘Vibrion septique’ a pathogenic clostridium responsible
shown to be viruses that multiply in bacterial cells. for gangrenous conditions in animals and demonstrated
Intensive study of the interaction of bacteriophage and that it was an obligate anaerobe. Within a few years it
bacterium by Delbru¨ck and Hershey in the early 1940s becamepossibletoobtainpureculturesofmanysortsof
contributed much to the knowledge of viral infections bacteria by colony selection on solid media and then to
8 Thebacteria:historicalintroduction
Figure3BacteriologicalSection,CongressofHygieneandDemography,London,1891.
collect reliable data about their phenotypic characters. The twentieth century was the time when both pure
Accounts of their growth on various media under and applied microbiology emerged as a science and
differentphysicalconditionsweresoonsupplementedby produced radical developments across the whole field of
informationabouttherangeoftheirfermentativeaction biology. The most striking development has been the
onorganic compounds andtheproducts offermentation emergence of molecular biology and the way that this
and by the identification of chemical requirements for has altered our understanding of biology and medicine.
growth. Thus, the raw materials for systematic bacter- This revolution is still at an early stage, but its impacts
iology began to be accumulated and basic studies of can be seen clearly in approaches to bacterial classifica-
bacterialmetabolismcouldbegin. tionandtyping.
For more detailed accounts of the early history of
bacteriology, and for references, see Bulloch (1938),
SYSTEMATIC BACTERIOLOGY
Clark (1961), Lechevalier and Slotorovsky (1965), and
Foster(1970).
Definition of the bacteria
THE TWENTIETH CENTURY The applied microbiologists of the time of Pasteur and
Koch were not much interested in the classification of
The last years of the twentieth century were marked by the microorganisms they considered responsible for
a number of centenary retrospects; in the present fermentation or for communicable diseases. Contem-
context,themostimportantwerethoseoftheAmerican porary biologists recognized two kingdoms of living
Society for Microbiology founded in 1899 and the things, plants and animals, but were uncertain in which
Journal of Hygiene (now Epidemiology and Infection) to place the bacteria. In 1838, Ehrenberg had used the
founded in 1901. Both these events resulted in the term ‘bacteria’ to describe rod-shaped organisms visible
consideration ofimportant eventsin microbiology, some only with a microscope and considered them animals,
ofwhicharelisted inTable2 (Jokliket al.1999; ASM but F. Cohn in 1854 claimed them for the botanists and
1999). Haeckel in 1866 thought that they should be placed,
Systematicbacteriology 9
along with fungi, algae, and protozoa, in a third sortofevidencewasnotavailabletomicrobiologistsand
kingdom, distinct from plants and animals, the Monera the apparent absence of sexual reproduction in bacteria
or Protista. Haeckel’s view did not receive wide accep- meant that the biologists’ favored criterion for the defi-
tance and for the next 50 years and more the bacteria nitionofthespecies,self-fertility,wasdeniedthem.
were in a taxonomic limbo. Then, technical advances, After 1880, the ability to study bacteria in pure
notably the introduction of the electron microscope in cultureledtotherapidaccumulationofvastamountsof
1932 and of the phase-contrast microscope in 1935, led data about their phenotypic characters: colonial appear-
to the recognition, usually associated with the names of ance,growthonvariousmedia,nutritionalrequirements,
Stanier and van Niel (1941), that the bacteria and biochemical activities, serological relationships, patho-
certain bacteria-like blue–green algae differed from genicity for laboratory animals, and so on. Practical
most other microbes in that their genetic material was bacteriologists selected sets of key tests that seemed
not separated from the cytoplasm by a nuclear usefulinidentifyingorganismsofinteresttothemandin
membrane. many cases attached Linnaean binomial epithets to
This view was later formalized into the concept that species so characterized. What resulted was not a
thereweretwosortsoflivingthingsdifferingfundamen- general classification of bacteria but a series of mini-
tally in cellular structure (Murray 1962; Gibbons and classifications used by workers in laboratories studying
Murray1978): medical, agricultural, or various sorts of industrial
problems. There was a great deal of duplication in the
1 theProkaryotae,comprisingthebacteria(Eubacteria)
naming of species, and the intuitional handling of
andtheblue–greenalgae,whichwerenowrecognized
complex collections of data led to some uncertainties in
tobephototrophicbacteriaand
classificationandidentification.
2 the Eukaryotae, which included fungi, algae,
protozoa,andallthemetazoaoftheplantandanimal
kingdoms. NUMERICALTAXONOMY
The prokaryotes were characterized by the absence of a An alternative to seeking ‘key’ characters had been
membrane-bounded nucleus and also of cellular orga- proposed in 1763 by Adanson, a contemporary of
nellessuchasmitochondriaandchloroplasts.Aspointed Linnaeus, who considered that biological classification
out by Woese, the definition of bacteria as nonphoto- should be based on general similarity in phenotypic
trophic prokaryotes is based entirely on negative char- characters. He rejected ‘weighting’ and determined, for
acters and provides no grounds for distinguishing the each possible pair of individuals in a collection, the
conventionalbacteriafromtheso-calledArchaebacteria. proportion of all ascertainable characters that were in
Theseareorganismsthatinhabitenvironmentally‘hostile’ accord: the so-called ‘overall’ similarity. Adanson found
habitats and include methanogens, extreme halophiles, the manual computation of similarities between large
and thermoacidophiles; they are said to form a coherent numbers of pairs excessively laborious and his method
group of organisms with characteristic isoprenoid lipids could not be employed on a large scale until electronic
and cell-wall components (see Woese and Wolfe 1985) computersbecameavailable.Then,thenewdisciplineof
andtobesurvivalsfromanearliergeologicalera.Woese numerical taxonomy was developed (Sneath 1957a, b;
(1994) considers that genetic evidence (see section on Sneath and Sokal 1974) and applied to collections of
Bacterial genetics) should take precedence over cellular bacterialculturesthathadbeenstudiedextensively.This
anatomy in defining the relationships of the prokaryotes madegreatcontributionstobacterialclassificationatthe
andeukaryotestoeachotherandtotheseprimitiveforms. levels of species and genus by providing an objective
measure of the degree of similarity between large
numbers of cultures. However, it is remarkable how
Classification of bacteria
often numerical-taxonomic studies supported earlier
conclusions arrived at by the intuitional recognition of a
Linnaeus (1707–1778) classified plants and animals ‘good’ classification as one that placed like organisms in
according to a hierarchical system based on Aristotle’s the same taxon. Some taxonomists, for example Cowan
theory of logical division (see Cain 1962) by placing (1962), expressed the view that the bacterial species was
individualsthatwerealikein‘essential’charactersinthe simplyaman-madeartifact,albeitausefulone,designed
same species and then constructing genera and other to put phenotypic data into manageable form. Numer-
higher taxa on the basis of progressively greater differ- ical taxonomy provided a powerful impetus to the ‘anti-
ences in characters. The selection of essential characters essentialist’ view of bacterial classification, but the prac-
(‘weighting’)wasatfirstmadeaccordingtotheintuition titioners of two other disciplines, chemotaxonomy and
of the classifier, but post-Darwinian biologists used the bacterialgenetics,continuetosearchfor‘keycharacters’
fossil record, often supplemented by embryological that might form a basis for a broad classification of
evidence, to construct classifications of plants and microorganisms (see Taxonony and nomen-
animals that were wholly or in part phylogenetic. This clatureofbacteria).
10 Thebacteria:historicalintroduction
Antigenic specificity and bacteria, first described by Boivin and his associates at
chemotaxonomy the Institut Pasteur in Paris in 1932–35. These were
complex macromolecules in the cell envelope
comprising:
In the early years of the twentieth century the antibody
response to bacterial antigens had been studied inten- . apolysaccharideresponsibleforantigenicspecificity
sively in vitro (Parker 1998). In the 1920s, evidence . alipidconferringtoxicity,and
begantoappearofthechemicalnatureofsomeofthese . a protein that, when linked to the polysaccharide,
antigens. This was investigated eagerly by medical rendereditantigenic.
bacteriologistsbecausetheantigensinquestionappeared
Studies of the amino-acid composition of the cell walls
to have some association with pathogenicity. Thus, a
of gram-positive bacteria by Cummins and Harris in
great deal of information accumulated about certain
1956 led to the recognition by Ghysen in 1965 of the
classesofantigenicmacromoleculesandsomeofthiswas
structure of their main component, the peptidoglycan
ofsignificanceforbacterialclassification.
or mucopeptide. In 1972, Schleifer and Kandler showed
From 1923 onwards, Avery and Heidelberger, at the
that similarities in the cross-linking of the main compo-
Rockefeller Institute in New York, studied the type-
nents of the peptidoglycan molecule were of value in
specific capsular polysaccharides of pneumococci and
establishing relationships between bacterial genera that
showed that antibodies to them conferred type-specific
would have been difficult to ascertain by conventional
immunity on experimental animals. Rebecca Lancefield,
serological means. It has since been noted that all
in the same laboratory, described in 1933 the so-called
eubacterial peptidoglycans contain N-acetyl muramic
group polysaccharides from the cell walls of hemolytic
acid but that this is absent from the cell walls of
streptococci; some of these characterized streptococcal
archaebacteria.
groups that caused disease only in certain species of
Since 1970 the chemical study of bacterial macro-
mammals. These polysaccharides had several characters
molecules has advanced rapidly. New information
incommon:
about the distribution of particular classes of lipids and
. Though determining the specificity of the antibody
isoprenoid quinones has provided grounds for estab-
response,theywereunabletoelicititwhenseparated
lishing relationships between higher taxa of gram-
from the bacterial body and purified; in 1921 Land-
positive bacteria and for distinguishing eubacteria from
steinercoinedtheterm‘hapten’forsuchmolecules.
archaebacteria (for references see Jones and Krieg
. The specificity of the antibody response to them was
1984).
relatively limited. Pneumococcal polysaccharides, for
Protein antigens, when studied by conventional sero-
example, though defining clear-cut serotypes among
logical methods, showed such a narrow specificity as to
pneumococci, cross-reacted widely with poly-
limit their value to the identification of species or sero-
saccharides of otherwise dissimilar bacteria and even
types. Recent studies of the chemistry of some widely
with nonbacterial polysaccharides, as shown by
distributed classes of protein, e.g. the cytochromes
Heidelberger, Austrian, and colleagues. This was
(Jones 1980), have revealed differences relevant to the
explained by the limited repertoire of specificities
general classification of bacteria. The increasing ability
provided by the sequence of sugars in the terminal
to determine the sequence of amino acids in individual
part of the polysaccharide chain. The role of the
proteins will add information to that provided by
terminal sugars as antigenic determinants was further
antigenic analysis. If a constant rate of mutation is
illuminated by the work of McCarty and Krause on
assumed,thenthismightbethoughttoprovideevidence
the cross-reactions between streptococcal group anti-
oftheevolutionary‘distance’betweentaxa.Suchconsid-
gens.
erationsmaybeattractivetothosewhofavoraphyloge-
. Though sometimes clearly associated with virulence,
neticapproachtobacterialclassification.
the polysaccharides were not toxic for experimental
animals. Bacterial genetics
In 1943, Rebecca Lancefield described a class of type-
specific cell wall protein antigens in Streptococcus At the beginning of the twentieth century it was gener-
pyogenes. Like other proteins, they were fully antigenic ally recognized that the characters of bacterial strains in
when extracted and purified. Antibodies to them were culture might vary, either temporarily, in response to
highly specific and conferred type-specific immunity. changes in the environment (‘adaptation’), or perma-
Though nontoxic, these M proteins determined patho- nently,independentofenvironmentalconditions(‘muta-
genicitybyinterferingwithphagocytosis. tion’). The latter phenomenon suggested the possession
Certain other cell-bound bacterial constituents proved by bacteria of a genetic system analogous to that of
to have toxic properties when injected into animals. larger organisms, but proof of this was lacking in the
These included the endotoxins of gram-negative absenceofadistinctnuclearapparatus.