SCOPE AND HISTORICAL DEVELOPMENTS IN MICROBIOLOGY...SCOPE AND HISTORICAL DEVELOPMENTS IN...

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SCOPE AND HISTORICAL DEVELOPMENTSIN MICROBIOLOGY

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The bacterium Escherichia coli

“Science contributes to our culture in many ways, as acreative intellectual activity in its own right, as a light whichhas served to illuminate man’s place in the uni-verse, andas the source of understanding of man’s own nature”

—John F. Kennedy (1917–63)The President of America

INTRODUCTION AND SCOPE

MICROBIOLOGY is a specialized area of biology (Gr. bios-life+ logos-to study) that concerns with thestudy of microbes ordinarily too small to be seen without magnification. Microorganisms aremicroscopic (Gr. mikros-small+ scopein-to see) and independently living cells that, like humans, livein communities. Microorganisms include a large and diverse group of microscopic organisms that existas single cell or cell clusters (e.g., bacteria, archaea, fungi, algae, protozoa and helminths) and theviruses, which are microscopic but not cellular. While bacteria and archaea are classed as prokaryotes(Gr. pro-before+ karyon-nucleus) the fungi, algae, protozoa and helminths are eukaryotes (Gr. eu-trueor good+ karyon-nucleus). Microorganisms are present everywhere on earth, which includes humans,animals, plants and other living creatures, soil,water and atmosphere.

Microorganisms are relevant to all of our lives in a multitude of ways. Sometimes, the influenceof microorganisms on human life is beneficial, whereas at other times, it is detrimental. Forexample, microorganisms are required for the production of bread, cheese, yogurt, alcohol, wine,beer, antibiotics (e.g., penicillin, streptomycin, chloramphenicol), vaccines, vitamins, enzymes andmany more important products as shown in the Tables 1.1, 1.2, and 1.3. Many products of microbescontribute to public health as aids to nutrition, other products are used to interrupt the spread ofdisease, still others hold promise for improving the quality of life in the year’s ahead.

Section A: Basic Microbiology

A TEXTBOOK OF BASIC AND APPLIED MICROBIOLOGY2

Table 1.1: Major antibiotics and their microbial sources

Antibiotic Microbial source

Bacitracin Bacillus licheniformisCephalosporin Cephalosporium acremoniumChloramphenicol Streptomyces venezuelaeCycloheximide Streptomyces griseusCycloserine Streptomyces orchidaceusErythromycin Streptomyces erythraeusGriseofulvin Penicillium griseofulvumKanamycin Streptomyces kanamyceticusLincomycin Streptomyces lincolnensisNeomycin Streptomyces fradiaeNystatin Streptomyces nourseiPenicillin Penicillium chrysogenumPolymyxin B Bacillus polymyxaStreptomycin Streptomyces griseusTeicoplanin Actinoplanes teichomyceticusTetracycline Streptomyces rimosus

Vancomycin Streptomyces orientalis

Table 1.2: Major industrial enzymes from bacteria, molds and yeasts and their applications

Enzyme Microorganism Application

Bacterial Enzymes

Amylase (α and β ) Bacillus Starch coatings (paper), desizing(textiles), removal of stains, detergents(drycleaning)

Glucose isomerase Bacillus, Streptomyces Fructose syrupPenicillin amidase Bacillus PharmaceuticalProtease Bacillus Detergent, spot removing, desizing,

wound cleaning

Mold Enzymesα-Amylase Aspergillus Baking (Bread)Glucoamylase Aspergillus, Rhizopus Syrup and glucose manufacture,

digestive aid (pharmaceutical)Rennet (aspartic proteinases) Mucor miehei CheesePectinase Aspergillus, Sclerotinia DrinksProtease (aspartic proteinases) Aspergillus BakingCellulase Aspergillus, Trichoderma Liquid, coffee concentrates, digestive

aid, degradation of wood or wood by-products

SCOPE AND HISTORICAL DEVELOPMENTS IN MICROBIOLOGY 3

Enzyme Microorganism Application

α-Galactosidase Aspergillus niger Pharmaceutical (helps in digestion(commercial name Beano) of sugar in humans)

Yeast Enzymes

Invertase Saccharomyces Confectionary

Lactase (β-galactosidase) Kluyveromyces Dairy

Raffinase (α-galactosidase) Saccharomyces Food

Table 1.3: Fermented foods from microorganisms

Fermented Substrate Microorganism Country/Food region

Idli Rice and Urad bean Leuconostoc mesenteroides, IndiaStreptococcus faecalis

Ang-kak Rice Monascus purpureus ChinaGari Cassava Corynebacterium West Africa

manihot, Geotrichumcandidum

Kaffir beer Sorghum caffrorum Lactobacillus delbrueckii South Africaor Eleusine coracana Saccharomyces cerevisiae

Kefir Milk Lactobacillus and Yeast Russia

Yoghurt Milk Streptococcus ther- Worldwidemophilus, Lactobacillusbulgaricus

Cheese Milk Penicillium roqueforti WorldwideP. camemberti

Microbes are also an important and essential component of an ecosystem. Molds and bacteriaplay key roles in the cycling of important nutrients in plant nutrition particularly those ofcarbon, nitrogen and sulphur. Bacteria referred to as nitrogen fixers live in the soil where theyconvert vast quantities of nitrogen in air into a form that plants can use. Microorganisms alsoplay major roles in energy production. Natural gas (methane) is a product of bacterial activity,arising from the metabolism of methanogenic bacteria. Microoragnisms are also being used toclean up pollution caused by human activities, a process called bioremediation (the introductionof microbes to restore stability to disturbed or polluted environments). Bacteria and fungihave been used to consume spilled oil, solvents, pesticides and other environmentally toxicsubstances.

Microorganisms have also harmed humans and disrupted societies over the millennia. Microbialdiseases undoubtedly played a major role in historical events, it was in the year 1347 when plagueor ‘black death’ struck Europe and within 4 years killed 25 million people, that is, one third ofthe population. Some of the common human diseases caused by bacteria, fungi (molds and yeasts),protozoa, helminths are shown in the Tables 1.4–1.7.


Table 1.4: Human diseases caused by bacteria

Type Species Disease

Spirochetes Treponema pallidum SyphilisBorrelia recurrentis Relapsing feverBorrelia burgdorferi Lyme diseaseLeptospira interrogans Leptospirosis

Helical, vibrioid, Gram- Campylobacter jejuni Food borne campylobacter enteritisnegative bacteria Helicobacter pylori Peptic ulcer and chronic gastritis

(=Campylobacter pylori)

Gram-negative aerobic Legionella pneumophila Legionnaires’ diseaserods and cocci Neisseria gonorrhoeae Gonorrhoea

Neisseria meningitidis Meningococcal meningitisBrucella melitensis BrucellosisBordetella pertussis Whooping coughFrancisella tularensis Tularemia (Rabbit fever)

Facultatively aerobic, Escherichia coli Oppurtunistic infectionsGram-negative rods Salmonella typhi Typhoid fever

Shigella dysenteriae Bacillary dysentry (Shigellosis)Klebsiella pneumoniae Pneumonia, MeningitisProteus sp. Urinary tract infectionsYersinia pestis Bubonic plagueVibrio cholerae CholeraHaemophilus influenzae Meningitis, Ear infectionsGardnerella vaginalis Vaginitis

Rickettsias and Rickettsia rickettsiae Rocky mountain spotted feverChlamydias Rickettsia prowazekii Epidemic typhus

Rickettsia typhi Murine typhusCoxiella burnetii Q-FeverChlamydia trachomatis TrachomaChlamydia psittaci Ormithosis (Psittacosis)Chlamydia pneumoniae Pneumonia

Mycoplasmas Mycoplasma pneumoniae Primary atypical pneumonia

Gram-positive cocci Staphylococcus aureus Boils, wound infections, Toxic shocksyndrome, Food poisoning, Impetigo

Streptococcus pneumoniae Pneumococcal pneumoniaStreptococcus pyogenes Strep throat, Glomerulonephritis,

Rheumatic fever, ImpetigoStreptococcus mutans Dental caries

(Contd.)


Type Species Disease

Spore forming Gram- Bacillus anthracis Anthrax

positive rods and cocci Clostridium tetani Tetanus

Clostridium perfringens Gas gangrene

Clostridium botulinum Botulism

Clostridium difficile Pseudomembranous colitis

Regular, non-sporing Lactobacillus sp. Normal human flora

Gram-positive rods Listeria monocytogenes Listeriosis

Irregular, non-sporing, Corynebacterium diphtheriae Diphtheria

Gram-positive rods Propionibacterium acne Acne

Mycobacteria (Acid- fast Mycobacterium tuberculosis Tuberculosis

organisms) Mycobacterium leprae Leprosy

Table 1.5: Human diseases caused by fungi

Disease Pathogen

(A) Superficial mycoses

Black piedra Piedraia hortae

White piedra Trichosporon beigelii

Dandruff or Tinea versicolor Malassezia furfur (Pityrosporum ovale)

(B) Dermatomycoses ( cutaneous mycoses)

Tinea capitis (Ringworm) Microsporum audouinii

Tinea pedis (Athlete’s foot) Trichophyton spp.

Tinea cruris (Jock itch) Epidermophyton floccosum

Tinea unguium (Ringworm of nails) Trichophyton rubrum

(C) Subcutaneous mycoses

Chromoblastomycosis Fonsecaea pedrosoi (Phialophora verrucosa)

Maduromycosis Madurella mycetomatis

Sporotrichosis Sporothrix schenckii

(D) Systemic mycoses (deep mycoses)

Blastomycosis Blastomyces dermatitidis (Ajellomyces dermatitidis)

Coccidioidomycosis (valley fever) Coccidioides immitis

Cryptococcosis Cryptococcus neoformans (Filobasidiella neoformans)

Histoplasmosis Histoplasma capsulatum

(Contd.)


Disease Pathogen

(E) Opportunistic mycoses

Aspergillosis Aspergillus fumigatus

Candidiasis (oral, napkin (diaper) Candida albicans

candidiasis, Candidal vaginitis)

Pneumocystis pneumonia (PCP) Pneumocystis jiroveci (P.carinii)

Zygomycosis Mucor and Rhizopus spp.

(F) Food poisoningErgotism (ergot poisoning) Claviceps purpurea

Table 1.6: Human diseases caused by protozoans

Phylum Pathogen Disease

Apicomplexa Babesia microti Babesiosis

Plasmodium falciparum, Malaria

P. ovale, P. vivax, P. malariae

Toxoplasma gondii Toxoplasmosis

Cryptosporidium parvum Cryptosporidiosis

Rhizopoda Acanthamoeba sp. Amoebic keratitis

Entamoeba histolytica Amoebic dysentery

Naegleria fowleri Microencephalitis

Mastigophora (Flagellata) Giardia lamblia (G. Intestinalis) Giardiasis

Trichomonas vaginalis Protozoal vaginitis

Trypanosoma brucei African sleeping sickness

Trypanosoma cruzi Chaga’s disease

Ciliophora (Ciliata) Balantidium coli Balantidial dysentery

Table 1.7: Human diseases caused by helminths


Platyhelminthes Paragonimus westermanni Paragonimiasis(Lung fluke)

Schistosoma sp. (Blood flukes) Schistosomiasis

Clonorchis sinensis Clonorchiasis(Chinese liver fluke)

(Contd.)



Taenia saginata (Beef tapeworm) Taeniasis

Taenia solium (Pork tapeworm) Taeniasis

Hymenolepsis nana Hymenolepasis(Dwarf tapeworm)

Diphyllobothrium latum Diphyllobothriasis(Fish tapeworm)

Echinococcus granulosus Echinococcosis(Dog tapeworm)

Fasciola hepatica Fascioliasis(Sheep liver fluke)

Nematoda (Roundworms) Strongyloides stercoralis Strongyloidiasis(Threadworm)

Ascaris lumbricoides Ascariasis(roundworm)

Necator americanus (hookworm) New world hookworm disease

Ancylostoma duodenale Old world hookworm disease

(hookworm)

Enterobius vermicularis Pinworm feotalism(Pinworm)

Trichuris trichiura Trichuriasis(Whipworm)

Trichinella spiralis Trichinosis(Trichinaworm)

Wuchereria bancrofti Elephantiasis or bancroftian

filariasis

Dirofilaria immitis (Heartworm) Filariasis

HISTORICAL DEVELOPMENTS IN MICROBIOLOGY

The beginnings

The study of microorganisms, or microbiology began when the first microscopes were developed in1665 by the English scientist, Robert Hooke who viewed many small objects and structures using asimple lens that magnified approximately 30 times. His specimens included the eye of a fly, a beestinger, and the shell of a protozoan. Hooke also examined thin slices of cork, which was the bark ofa particular type of oak tree. He found that cork was made of tiny boxes that Hooke referred to as‘cells’. He published his work in a book Micrographie which contained a miscellany of his thoughtson chemistry as well as a description of the microscope and its uses. Hooke in 1665 described thefruiting structures of molds. Thus, Robert Hooke was the first person to describe microorganisms.


Antony vanLeeuwenhoek

(1632-1723)

MICROFOCUS 1.1

Antony van Leeuwenhoek (pronounced Layu-wen- hoek) was born onOctober 24, 1632 in Delft, Holland (now Netherlands). In 1674, he made firstobservation of microoraganisms and was the first person to observe andaccurately describe and measure bacteria and protozoa, termed by him, as“animalcules” which he thought were tiny animals. In 1677, he became thefirst person to describe spermatozoa and was one of the earliest to describered blood corpuscles. In 1680, he was elected a fellow of the Royal Societyof London, and with Isaac Newton and Robert Boyle, he became one of thefirst famous men of his time. He died on August 30, 1723 at the age of 90.Because of his extraordinary contribution to microbiology, he is consideredas the father of bacteriology and protozoology.

Unicellular life was first described just a few years after Hooke recorded his observations ofthe microscopic world. Antony van Leeuwenhoek (Microfocus 1.1) was a Dutch merchant whopolished grains of sand into lenses which were able to magnify 300 times and added a simple focusmechanism. With his microscope, van Leeuwenhoek viewed rain and pond water, infusions madefrom peppercorns, and scrapings from his teeth in the year 1674 and termed the tiny microorganismsas ‘animalcules’. In 1676, van Leeuwenhoek sent his drawings to the Royal Society of London. Thishas special significance to microbiology because it contained his first detailed description of themicroorganism.

The transition period

Biology of the 1700s was a body of knowledge without a focus. It consisted of observations of plantand animal life and the attempts by scientists to place the organisms in logical order. The dominantfigure of the era was Carolus Linnaeus (1707–1778), a Swedish botanist who brought all the plantand animal forms together under one Binomial nomenclature (naming of an organism by twonames—the genus and species) system of classification scheme. His book, Systema naturae, wasfirst published in 1735.

Discovery of the microscopic world raised some interesting queries and eventually ledscientists to question some of the long-held beliefs. At that time in history, the scientific communityused a theory known as ‘spontaneous generation’ (the doctrine that holds that lifeless objectsgive rise to living organisms) to explain the apparently magical origins of life. The theory proposedthat simple life forms arose spontaneously from non-living materials and had its basis in thefindings of Aristotle in the fourth century BC.

Although most people accepted spontaneous generation, the theory did have some strongopponents. Among the first to dispute the theory of spontaneous generation was the Italianscientist, Francesco Redi (1626–1697). He reasoned that flies had reproductive organs whileobserving van Leeuwenhoek’s drawings. He suggested that flies land on pieces of exposed meatand lay their eggs, which then hatch to maggots. This would explain the ‘spontaneous’ appearanceof maggots. In the 1670s, Redi performed a series of tests in which he covered jars of meat withfine lace, thereby preventing the entry of flies. The meat would not produce maggots as it wasprotected and Redi temporarily put to rest the notion of spontaneous generation.


Edward Jenner(1749–1823)

Although Redi’s work became widely known, the doctrine of spontaneous generation was toofirmly entrenched to be abandoned. In 1748, British clergyman, John Needham (1713–81) put forththe notion that in flasks of mutton gravy, microorganisms arise by spontaneous generation. He evenboiled several flasks of gravy and sealed the flasks with corks as Redi had sealed his jars. Still,the microorganisms appeared.

Italian scientist Abbe Lazzaro Spallanzani (1729–99) criticized Needham’s work. In 1767,Spallanzani boiled meat and vegetable broths for long period of time and then sealed the necksby melting the glass. As control experiments, he left some flasks open to the air, stoppered someloosely with corks, and boiled some briefly, as Needham had done. After two days, he found thecontrol flasks swarming with organisms, but the sealed flasks had no organisms. Needhamcountered that Spallanzani had destroyed the ”vital force” of life with excessive amounts of heat.

While the spontaneous generation was being debated, some of the scientists were concernedabout the transmission of the disease. In 1546, Italian scientist Girolamo Fracastoro held the conceptthat “contagion is an infection that passes from one thing to another”. He recognized three forms ofpassage, namely contact, lifeless objects, and air (Table 1.8). This notion received little credibility thatmicroorganisms were the substance of contagion. The German Athanasius Kircher was paid littleattention when he reported “microscopic worms” in the 1600s in the blood of plague victims.Christian Fabricius was also neglected when he suggested in 1700s that fungi might be the cause ofrust and smut diseases in plants. Edward Jenner (Microfocus 1.2) was accorded honours in 1798when he discovered immunization for smallpox, despite the fact that he could not explain the causeof the disease. In 1847, Hungarian physician, Ignaz Semmelweis reported that blood poisoningagent was transmitted to maternity patients by physicians fresh from performing autopsies in themortuary. Semmelweis showed that hand washing in chlorine water could stop the spread of disease.His call for disinfection practices were however largely unheeded because it implied that physicianswere at fault.

MICROFOCUS 1.2

Edward Jenner, born in 1749, was an English physician from Berkeley,Gloucestershire, England. His great gift to mankind was his vaccine for smallpox(characterized by production of skin lesions called pox (pocks), caused by Variola,belonging to the category of pox viruses). Jenner’s discovery, that a lesspathogenic agent could confer protection against a more pathogenic one, isespecially remarkable in view of the fact that microscopy was still in its infancyand the nature of the virus was not known. The modern era of vaccines andvaccination, thus began in 1798 with Edward Jenner’s use of cowpox as avaccine against smallpox.

John Snow, a British physician, traced the source of cholera to the municipal water supply ofLondon during an 1854 outbreak. He reasoned that by avoiding the contaminated water source,people could avoid the disease. Snow’s recommendations were adopted and the spread of diseasewas halted. Both Semmelweis and Snow drew attention to the fact that a poison or unseen objectin the environment was responsible for the disease, but the proof was still lacking. Joseph Lister(Microfocus 1.3) in 1867, developed a system of antiseptic surgery designed to prevent micro-organisms from entering wounds.


Joseph Lister(1827–1912)

MICROFOCUS 1.3

Joseph Lister was born in 1827. He developed a system of antiseptic surgerydesigned to prevent microorganisms from entering wounds in 1867. In 1878,Lister studied the lactic acid fermentation of milk and demonstrated the specificcause of milk souring. He also developed a method for isolating a pure culture of abacterium, named as Bacterium lactis. Because of his notable contribution-firstintroduction of principles of sterile surgery in medical practice, which was so farreaching in its effects—Lister will always be known as the Father of antisepticsurgery. He died at the age of 85 in the year 1912.

Table 1.8: Some early observations in microbiology before the dawn of golden era

Time period Investigator Observations

Fourth Century Aristotle Living things do not need parents, spontaneous generationBC. apparently occurs.

Mid 1500s Fracastoro “Contagion” passes among individuals, objects and air.

Mid 1600s Kircher “Microscopic worms” are present in blood of plague victims.

Mid 1600s Francisco Redi Fly larvae arise by spontaneous generation.

Late 1600s Van Leeuwenhoek Microscopic organisms are present in numerous environ-ments.

Early 1700s Christian Fabricius Fungi cause rust and smut diseases in plants.

Early 1700s Joblot Existence of various forms of protozoa.

Mid 1700s John Needham Microorganisms in broth arise by spontaneous generation.

Mid 1700s Lazzaro Spallanzani Heat destroys microorganisms in broth.

Late 1700s Edward Jenner Recoverers from cowpox do not contract smallpox.

Mid 1800s Ignaz Semmelweis Chlorine disinfection prevents disease spread.

Mid 1800s John Snow Water is involved in disease transmission.

The classical golden age of microbiology (1854–1914)

The science of microbiology blossomed during a period of about 60 years referred to as the GoldenEra of Microbiology. The period began in 1857 with the work of Louis Pasteur and continued into thetwentieth century until the advent of World War I. During this period, numerous branches ofmicrobiology were laid for the maturing process that has led to modern microbiology.

Louis Pasteur (Microfocus 1.4) was the first to report the role of microorganisms in fermentationin 1848, he achieved distinction in organic chemistry for his discovery that tartaric acid, a four-carbon organic compound, forms two different types of crystals. Pasteur successfully separated thecrystals while looking through the microscope. In 1854, at the age of 32, he was appointed Professorof Chemistry at the University of Lille in northern France.

Pasteur in 1857 unravelled the mystery of sour wines. In a classic series of experiments, Pasteurclarified the role of yeasts in fermentation of fruits and grains resulting in the production of alcohol.


He also found that bacteria were responsible for spoilage of wine. He firmly disproved thespontaneous generation doctrine by his Swan-Neck Flask experiment (Fig. 1.1). He proposed germtheory of disease and discovered the existence of life in the absence of free oxygen (anaerobicgrowth). He showed that mild heating could be used to kill microorganisms in broth (pasteurization).Pasteur suggested methods to control pebrine disease in silkworm, isolated the causative agent ofcholera (Vibrio cholerae) and rabies (Lyssa) virus and also developed anti rabies and anthrax(Bacillus anthracis) vaccines.

Although Pasteur failed to relate a specific organism to a specific disease, his work stimulatedothers to investigate the nature of microorganisms and to ponder their association with disease.German botanist, Ferdinand Cohn (1828–98), discovered that bacteria multiply by dividing intotwo cells. He also observed that certain bacteria form an extremely resistant structure calledendospore in the cell.

Fig. 1.1: Pasteur’s experiment with the swan-necked flasks to disprove spontaneous generation. (a) Life appearedin broth in flasks exposed to air. (b) No life appeared in sealed flasks. (c) No life appeared in flasks where the neckwas continuously heated. (d) No life appeared in flasks when the microorganisms were trapped in the bend of the sidearm.


Louis Pasteur(1822–1895)

MICROFOCUS 1.4

Louis Pasteur- Notable Contributions

1857 – Lactic acid fermentation is due to a microorganism1860 – Yeasts are involved in alcoholic fermentation1861 – Disproved the theory of spontaneous generation1861 – Introduction of the terms aerobic and anaerobic for yeasts.

Production of more alcohol in the absence of oxygen duringsugar fermentation- The Pasteur Effect

1862 – Proposed germ theory of disease1867 – Pasteur devised the process of destroying bacteria known

as pasteurization.1881 – Development of anthrax vaccine. Resolved Pebrine

problem of silkworms.1885 – Development of a special vaccine for rabies (the Pasteur

treatment)Louis Pasteur, a French microbiologist, was born on December 27,

1822 in Dole, France. He studied at the French school, the Ecole Normale Superieure. In 1848, he achieveddistinction in organic chemistry for his discovery that tartaric acid, a four carbon organic compoundforms two different types of crystals. Using a microscope, Pasteur successfully separated the crystals anddeveloped a skill that would aid his later studies of microorganisms. In 1854, at the young age of 32, hewas appointed Professor of Chemistry at the University of Lille in northern France. He died in 1895, atthe age of 73.

Cohn described the entire life cycle of Bacillus (vegetative cell → endospore → vegetative cell). Heis credited with the use of cotton plugs for closing flasks and tubes to prevent the contamination ofsterile culture media. In 1866, Cohn studied the filamentous sulphur-oxidizing bacterium Beggiatoamirabilis and was the first to identify the small granules present in the cell that are of sulphur,produced from the oxidation of H2S.

The definite proof of the germ theory of disease was offered by Robert Koch (Microfocus 1.5)from East Russia, now part of Germany. Koch’s primary interest was anthrax, a deadly blooddisease in cattle and sheep. In 1875, he injected mice with the blood of diseased sheep and cattle.He then performed meticulous autopsies and noted that the same symptoms appeared regularly.He isolated a few rod shaped bacilli from a mouse’s blood by placing the bacilli in the sterileaqueous humor from an ox’s eye. The symptoms of anthrax appeared within hours. Koch autopsiedthe animals and found their blood swarming with bacilli. He reisolated the bacilli in sterile aqueoushumor. Koch’s procedures came to be known as Koch’s postulates (Fig. 1.2). The four postulatesare:

• The suspected microorganism must always be found in diseased but never in healthyindividuals.

• The microorganism must be isolated in pure culture (one free of all other types of microbes) ona nutrient medium.

• The same disease must result when the isolated microorganism is inoculated into a healthyhost.

• The same organism must be reisolated from the experimentally infected host.


Robert Koch(1843–1910)

Fig. 1.2: The diagrammatic representation of the Koch’s criteria for proving that a specific microorganism causes aspecific disease, i.e., the Koch’s postulates.

MICROFOCUS 1.5

Notable contributions of Robert Koch1876 – Koch demonstrated that anthrax is caused by Bacillus anthracis.1877 – Methods for staining bacteria, photographing and preparing

permanent visual records on slides.1881 – Koch developed solid culture media and the methods for studying

bacteria in pure cultures.1882 – Isolated the bacterium—Mycobacterium tuberculosis—that causes

tuberculosis.1882 – Use of agar as a support medium for solid culture in Koch’s lab by

Hesse.1883 – Isolation of Vibrio cholerae, the cause of cholera.1883 – Verification of the germ theory of disease by relating a specific

organism to the specific disease.1884 – Koch put forth his postulates—known as Koch’s postulates.

Robert Koch was born in Hanover, Germany in 1843. For his contributions on tuberculosis, Robert Kochwas awarded the 1905 Nobel Prize for Physiology or Medicine. He died in the year 1910 at the age of 67.


Koch chanced to observe in 1880 that a slice of potato contained small masses of bacteria,which he termed colonies. Colonies contained millions of just one kind of bacteria. Koch con-cluded that bacteria could grow and multiply on solid surfaces, and he added gelatin to his brothto prepare a solid culture medium. He then inoculated bacteria to the surface and set the mediumaside to incubate. When colonies of the same bacterium grew together, a pure culture (anaccumulation of one type of microorganism formed by the growth of colonies of the organism)formed. Koch could now inoculate laboratory animals with a pure culture of bacteria and be certainthat only one species of bacterium was involved. His work also proved that bacteria, not toxinsin the broth were the cause of the disease.

Gelatin was replaced with agar as a solidifying agent in the culture media as suggested byFannie Eilshemius Hesse, wife of Walter Hesse, an assistant in the Koch’s lab. Petri dish was alsoinvented about this time by Julius Petri, one of Koch’s assistants. In 1881, Koch demonstrated hispure culture techniques in the International Medical Congress.

Koch’s proof of the germ theory was presented in 1876. Within two years, Pasteur had verifiedthe proof and gone a step further. He reported that bacteria were temperature-sensitive becausechickens did not acquire anthrax at their normal body temperature of 420C but did so when theanimals were cooled down to 370C. He also recovered anthrax spores from the soil and pointed outthat cattle were probably infected during grazing. This explained the periodic recurrence of thedisease.

One of Pasteur’s more remarkable discoveries was made in 1880 when a group of inoculatedchickens failed to develop chicken cholera. He had been working on ways to enfeeble bacteria usingheat, different growth media, passages among animals, and virtually anything he thought mightweaken them. Finally, he had developed two cultures whose ability to cause disease was reduced.The trick was to suspend the bacteria in a mildly acidic medium and allow the culture to remainundisturbed for a long period of time.When it was inoculated to chickens and later followed bya dose of lethal cholera bacilli, the animals did not become sick. This principle is the basis for theuse of many vaccines for immunity. Pasteur applied the principle to anthrax in 1881 and foundhe could protect sheep against the disease.

Koch, isolated the tubercle bacillus, the cause of tuberculosis. In 1884, Koch’s associate GeorgeGafky, cultivated the typhoid bacillus, and that same year another coworker, Friederich Loeffler,isolated the diphtheria bacillus. In later years, Koch’s coworker, Emil von Behring, successfullytreated diphtheria by injecting antitoxin, a blood product (preparation of antibodies) obtained fromanimals given injections of the toxin. For his work, von Behring was awarded the first Nobel Prizein Physiology or Medicine.In 1885, Pasteur reached the zenith of his carrier when he successfullyimmunized young Joseph Meister against the dreaded disease rabies. Although he never saw theagent of rabies, Pasteur was able to cultivate it in the brains of animals and inject the boy withbits of the tissue. The experiment was a triumph for Pasteur because it fulfilled his dream ofapplying the principles of science to practical problems. A comparison of Pasteur and Koch’sachievements is given in the Table 1.9.

Other pioneers of microbiology

Shibasaburo Kitasato of Japan studied with Koch and successfully cultivated the tetanus bacillus,an organism that grows only in the absence of oxygen. One of the Pasteur’s associates was ElieMetchnikoff (Microfocus 1.6), who in 1884, published an account of phagocytosis, a defensiveprocess in which the body’s white blood cells engulf and destroy microorganisms.


Elie Metchnikoff(1845–1916)

Table 1.9: A comparison of contributions of Louis Pasteur and Robert Koch

Characteristic Louis Pasteur Robert Koch

Country of origin France Germany (Prussia)Preparatory Chemistry Medicineeducation

Initial Milk souring, beer, Cause of anthraxinvestigations wine fermentations

Accomplishments • Proposed germ theory of disease • Proved germ theory of disease

• Disproved theory of spontaneous • Developed cultivation methods forgeneration bacteria

• Developed immunization • Isolated bacterium that causestechniques tuberculosis

• Resolved pebrine problem of • Developed staining methods for bacteriasilkworms

• Developed rabies vaccine • Investigated cholera, malaria, sleepingsickness

Associates Roux, Yersin, Metchnikoff Gaffky, Loeffler, von Behring, Richard Pfeiffer

Nobel Prize No 1905 Nobel Prize in Physiology or Medicine

MICROFOCUS 1.6

Elie Metchnikoff, one of the associates of Louis Pasteur, was a Russian zoologistwho lived in Paris and did his work at the Institute Pasteur, France. He wasborn in Kharkor priovince of Ukraine (USSR) in 1845. By the 1860s he hadcompleted his formal studies in Embryology from various Universities ofKharkor, Russia, Germany and Italy. Metchnikoff coined the term“phagocytosis” which literally means” the eating of cells”. In 1884, he publishedaccount of phagocytosis, a defensive process in which the body’s white bloodcells (WBCs) engulf and destroy microorganisms. Thus, he formulated thebasic theory on which the science of immunology is founded: that the body isprotected from infection by leukocytes that engulf bacteria and other invadingorganism (cellular immunity). He became an administrator to the InstitutePasteur in 1888 and eventually became its director. He was awarded the NobelPrize in 1908. Metchnikoff’s notable contribution was on the Bacillus bulgaricustherapy and his underlying concept of health. Metchnikoff belived thatstreptococci and lactobacilli in yogurt assume residence in the intestine andreplace organisms that contribute to aging. Despite eating large quantities of yogurt, Metchnikoff diedan early death, in 1916, at age seventy-one.

A Pasteur Institute scientist, Charles Nicolle, proved that typhus fever was transmitted by lice.Albert Calmette, also of the Institute, developed a harmless strain of the Tubercle bacillus used forimmunization. Jules Bordet, a Belgian bacteriologist isolated the bacillus of pertussis (whoopingcough) and developed the complement fixation test, a procedure once widely used in the diagnosisof disease.


Ronald Ross, an English physician working in the Far East in 1898 proved that mosquitoes werethe vital link in malaria transmission. The discovery earned him the 1902 Nobel Prize. AnotherEnglishman, David Bruce, isolated the cause of undulant fever. Bruce also showed that tsetse fliestransmit sleeping sickness. A third British subject, Almroth Wright, described opsonins, the chemicalsubstances that promote phagocytosis in the body.

In 1897, the Tokyo physician Masaki Ogata reported that rat fleas transmit bubonic plague.This discovery solved a centuries old mystery of how plague spread. A year later, Kiyoshi Shigaisolated the bacterium that causes bacterial dysentery, an important intestinal disease. Theorganism was later named Shigella.

The American microbiologists, Daniel E. Salmon and Theobald Smith, were among the firstto use heat killed bacteria for immunizations. Salmon later studied swine plague and lent his nameto Salmonella, the cause of typhoid fever. Smith showed that Texas fever, a disease of cattle, wastransmitted by ticks. The University of Chicago pathologist Howard Taylor Rickkets located theagent of Rocky Mountain spotted fever in the human bloodstream and demonstrated itstransmission via ticks. Another American, William Welch, isolated the gas gangrene bacillus at hislaboratory at John Hopkins University. Walter Reed led a contingent to Cuba and pinpointedmosquitoes as the insects involved in yellow fever transmission.

In addition, Winogradsky and Beijerinck began examining the role of non-infectious micro-organisms in the soil and reported that microorganisms play an important role in nitrogen, sulphurand carbon cycling as well as process of nitrogen fixation by symbiotic or free living soil bacteria.Iwanowsky and Beijerinck provided the first evidence for virus as infectious agent.

The advent of World War I in 1914 signaled a dramatic pause in microbiology research andbrought to an end the Golden Era of Microbiology.

The era of chemotherapy and microbial genetics

Paul Ehrlich in collaboration with Sakahiro Hata, discovered the drug, Salvarsan, an arsenobenzolcompound in 1910 for the treatment of syphilis caused by Treponema pallidum. Ehrlich laid importantfoundation of the era of chemotherapy which is defined as the use of chemicals that selectivelyinhibit or kill pathogens without causing damage to the victim.

Gerhard Domagk of Germany in 1935 reported that Prontosil, a red dye used for stainingleather, was active against pathogenic streptococci and staphylococci in mice even though it hadno effect against the same infectious agent in the test tube. The two French scientists Jacques andTherese Trefonel in the same year showed that the compound Prontosil was broken down withinthe body of the animal to sulphanilamide (sulpha drug) which was the true active factor. Domagkwas awarded Nobel Prize in 1939 for the discovery of the first sulpha drug.

The credit for the discovery of the first”wonder drug”, penicillin goes to a Scottish physicianand bacteriologist, Sir Alexander Fleming (Microfocus 1.7) in 1929 from the mold Penicilliumnotatum. Fleming discovered the first antibiotic which is a microbial product that can killsusceptible microorganisms and inhibit their growth. Sir Howard. W. Florey and Ernst B.Chain at Oxford University in 1941 developed methods for industrial production of penicillinin England. Fleming, Florey and Chain shared the Nobel Prize in 1945 for the discovery andproduction of penicillin.


Alexander Fleming(1881–1955)

MICROFOCUS 1.7

Alexander Fleming, a Scottish, was born in the year 1881. He was aphysician by training, but spent most of his time studying bacteria. SirAlexander Fleming, in 1922 discovered that lysozyme, an enzymefound in tears, saliva and sweat, could kill bacteria, the first bodysecretion shown to have chemotherapeutic properties. He in 1928discovered the first antibiotic (Gr. anti-against + bios- life, the microbialproduct that can kill susceptible microorganisms or inhibit theirgrowth), penicillin. In 1929, Alexander Fleming published his findingsin the paper describing penicillin and its effect on Gram-positivebacteria. Fleming died in 1955, at the age seventy-four.

At the time of World War II (1939–44), S. A. Waksman of Rutgers’ University, USA discoveredanother antibiotic, streptomycin along with Albert Schatz in 1944 from an actinomycete, Streptomycesgriseus. Waksman received the Nobel Prize in 1952 for his notable contribution and for the discoveryof streptomycin used in the treatment of tuberculosis, a bacterial disease caused by Mycobacteriumtuberculosis, that had been discovered by Robert Koch in 1882.

Dr. Paul R. Burkholder in 1947 isolated chloramphenicol (chloromycetin) from Streptomycesvenezuelae. Dr. B.M. Dugger in 1948 identified aureomycin from Streptomyces aureofaciens andterramycin was discovered by Finlay, Hobby and collaborators in 1950 from Streptomyces rimosus.Antibiotic production continues to be the important area of industrial research. Currently, there areover 8000 antibiotics known, of which only a few are being used as chemotherapeutic agents.

In 1943, Italian microbiologist Salvador Luria and the German physicist Max Dulbriick carriedout a series of experiments with bacteria and viruses. They used the bacterium Escherichia coli to addressa basic question regarding the nature of mutations, spontaneous or induced. Luria and Dulbriickshowed that bacteria could develop spontaneous mutations that generate resistance to viral infection.Besides the significance of their findings to microbial genetics, their use of E. coli as a microbial modelsystem showed to other researchers that these relatively simple microorganisms could be used to studygeneral principles of biology. The experiments carried out by Americans George Beadle and EdwardTatum, using the fungus, Neurospora, showed that one gene codes for one enzyme i.e., one-gene one-enzyme hypothesis. Oswald Avery, Colin Mcleod, and Maclyn McCarty, working with the bacteriumStreptococcus pneumoniae, suggested that deoxyribonucleic acid (DNA) is the genetic material in cells.In 1953, American biochemist Alfred Hershey and geneticist Martha Chase, using bacterial viruses,provided irrefutable evidence that DNA is the substance of genetic material. Joshua Lederberg(Microfocus 1.8) in 1958 received the Nobel Prize in Physiology or Medicine for his discoveriesconcerning genetic recombination and organization of genetic material in bacteria.

The small size of bacteria hindered scientists’ abilities to confirm that bacteria were “cellular” infunction. In the 1940s and 1950s, an electron microscope was developed that could magnify objectsand cells thousands of times more than typical light microscopes. With the electron microscopes, forthe first time bacteria were seen as being cellular like all other microbes, plants and animals. Howeverstudies showed that they were organized in a fundamentally different way from other organisms. Itwas shown that animal and plant cells contained a cell nucleus that stores the genetic information inthe form of chromosomes and was separated physically from other cell structures by a membrane


Dr. Joshua Lederberg

Carl Woese

envelope. This type of cellular organization is called eukaryotic (eu= true+karyon = kernel, nucleus).Microscopic observations of the Protista and Fungi had revealed that these organisms also had aeukaryotic organization.

MICROFOCUS 1.8

Dr. Joshua Lederberg was born on May 23, 1925 in Montclair, New Jersey.Joshua Lederberg is noted for two landmark discoveries in bacterial genetics:bacterial conjugation and transduction, both laying foundations for geneticengineering, modern biotechnology and genetic approaches to medicine.Interdisciplinary in his scientific interests and methods, he became a pioneerof Exobiology and the exploration of space, and was instrumental inintroducing computers and artificial intelligence into laboratory research andbiomedical communication. Lederberg, along with Beadle and Tatum, wasawarded the Nobel Prize at the age 33, for his discoveries concerning geneticrecombination and organization of the genetic material of bacteria. In additionto receiving the Nobel Prize, Lederberg has received many other awards andhonours. It can only be said that Joshua Lederberg single-handedly changedthe nature of bacterial genetics and changed the course of both genetics andbiochemistry.

Studies with the electron microscope revealed that bacterial cells had few of the cellular structurestypical of eukaryotic cells. They lacked a cell nucleus, indicating the bacterial chromosome was notsurrounded by a membrane envelope. Therefore, bacteria have a prokaryotic (pro= primitive + karyon= nucleus) type of cellular organization. Eubacteria and Archaea, thus, are prokaryotes.

The modern molecular biology era

By the 1970s, research on bacterial physiology, biochemistry and genetics had advanced to such anextent that it was possible to experimentally manipulate the genetic material of living organisms.With the invention of restriction enzymes, it became possible to introduce DNA from foreign sourcesinto bacteria and control its replication. This led to the development of fascinating field ofBiotechnology. In 1967, Carl Woese (Microfocus 1.9) originated the RNA World Hypothesis andalso discovered the extremophiles, Archaea. Prof Har Gobind Khorana (Microfocus 1.10) along withNirenberg and other coworker deciphered the genetic code and was awarded the Nobel Prize in1968. Many diseases that were previously thought to have only behavioural or genetic componentshave been found to involve microorganisms.

MICROFOCUS 1.9

Carl Woese, an American microbiologist, was born on July 15, 1928 in Syracuse,New York. He is famous for defining the Archaea (a new domain or kingdom oflife) in 1977 by phylogenetic analysis of 16S ribosomal RNA, a technique pioneeredby Woese and which is now standard practice. He is also the originator of RNAWorld Hypothesis in 1967, although not by name.


Prof. H.G.

Two Australians, Barry J. Marshall and Robin Warren won the 2005 Nobel Prize for showingthat bacterial infections of Helicobacter pylori (= Campylobacter pylori) and not the stress, is responsiblefor painful ulcers in the stomach and intestine.The 1982 discovery transformed peptic ulcer diseasefrom a chronic, frequently disabling condition to one that can be cured by a short regimen of antibioticsand medicines.

MICROFOCUS 1.10

Prof. Har Gobind Khorana was born on 2nd January, 1922 in Rajpura, Punjab,India. He was awarded the Nobel Prize in Physiology/Medicine in 1968 for hiscontribution to the elucidation of the genetic code. His research explained howmessages inscribed in genes are translated into proteins. He was also the firstperson to successfully synthesize a gene in 1970. This achievement establishedthe foundation for the Biotechnology industry. The proteomics is defined aswhere custom-designed genes are being widely used to engineer new plants andanimals.

At the same time, nucleic acid sequencing methods were developed which left its impact in allthe areas of biology. Sequencing technology helped microbiologists to reveal phylogenetic(evolutionary) relationships among prokaryotes, which led to evolutionary new concepts in the fieldof biological classification. The field of Genomics is also a contribution of sequencing technology, inwhich the comparative analysis of the genes of different organisms is carried out. The huge amountsof genomic information now in hand are leading to major advances in medicine, microbial ecology,industrial microbiology, and many other areas of biology. The genomics era has given birth to a newsubdiscipline, Proteomics. The proteomics is defined as the study of protein expression in cells. Thesignificance of such developments in molecular biology to all of biology is understood by the fact thatnumerous Nobel Prizes have been awarded to researchers for their work in this field as shown in thetable 1.10.

Table 1.10: Nobel Laureates in Physiology or Medicine since 1901

Year Investigator(s) Discovery

1901 Emil von Behring Serum therapy, especially its application against diphtheria

1902 Ronald Ross Malaria, by which he has shown how it enters the organism

1903 Niels Ryberg Finsen Treatment of diseases, especially lupus vulgaris, with

concentrated light radiation

1904 Ivan Pavlov Physiology of digestion

1905 Robert Koch Investigations and discoveries in relation to tuberculosis

1906 Camillo Golgi and Santiago Structure of the nervous system

Ramony Cajal

1907 Alphonse Laveran Role played by protozoa in causing diseases

1908 Ilya Metchnikoff and Work on immunity

Paul Ehrlich

(Contd.)



1909 Theodor Kocher Physiology, pathology and surgery of the thyroid gland

1910 Albrecht Kossel Cell chemistry, work on proteins, including the nucleic substances

1911 Allvar Gullstrand Dioptrics of the eye

1912 Alexis Carrel Vascular suture and the transplantation of blood vessels

and organs

1913 Charles Richet Anaphylaxis

1914 Robert Bárány Physiology and pathology of the vestibular apparatus

1919 Jules Bordet Discoveries relating to immunity

1920 August Krogh Capillary motor regulating mechanism

1922 Archibald V. Hill and Discovery relating to the production of heat in the muscle (Hill)Otto Meyerhof and discovery of the fixed relationship between the consumption

of oxygen and the metabolism of lactic acid in the muscle(Meyerhof)

1923 Frederick G. Banting Discovery of insulin

and John Macleod

1924 Willem Einthoven Mechanism of the Electrocardiogram

1926 Johannes Fibiger Discovery of the Spiroptera carcinoma

1927 Julius Wagner-Jauregg Therapeutic value of malaria inoculation in the treatment ofdementia paralytica

1928 Charles Nicolle Work on typhus

1929 Christiaan Eijkman and Discovery of the antineuritic vitamin (Eijkman) and discoverySir Frederick Hopkins of the growth stimulating vitamins (Hopkins)

1930 Karl Landsteiner Discovery of human blood groups

1931 Otto Warburg Nature and mode of action of the respiratory enzyme

1932 Sir Charles Sherrington Functions of neurons

and Edgar Adrian

1933 Thomas H. Morgan Role played by the chromosome in heredity

1934 George H. Whipple, Liver therapy in cases of anaemia

George R. Minot and

William P. Murphy

1935 Hans Spemann Organizer effect in embryonic development

1936 Sir Henry Dale and Chemical transmission of nerve impulsesOtto Loewi

1937 Albert Szent-Györgyi Biological combustion processes, with special reference to vitaminC and the catalysis of fumaric acid

1938 Corneille Heymans Role played by the sinus and aortic mechanisms in the regulationof respiration

1939 Gerhard Domagk Discovery of the antibacterial effect of prontosil

1943 Henrik Dam and Discovery of vitamin K and study on the chemical nature of

Edward A. Doisy vitamin K

(Contd.)



1944 Joseph Erlanger and Highly differentiated functions of single nerve fibres

Herbert S. Gasser

1945 Sir Alexander Fleming, Discovery of penicillin and its curative effect in variousErnst B. Chain and infectious diseasesSir Howard Florey

1946 Hermann J. Muller Production of mutations by means of X-ray irradiation

1947 Carl Cori, Gerty Cori Discovery of the course of the catalytic conversion of glycogenand Bernardo Houssay (Cori and Cori) and discovery of the part played by the hormone

of the anterior pituitary lobe in the metabolism of sugar (BernardoHoussay)

1948 Paul Müller High efficiency of DDT as a contact poison against severalarthropods

1949 Walter Hess Discovery of the functional organization of the interbrain as a

and Egas Moniz coordinator of the activities of the internal organs (Walter Hess)and discovery of the therapeutic value of leucotomy in certainpsychoses (Egas Moniz)

1950 Edward C. Kendall, Hormones of the adrenal cortex, their structure and biologicalTadeus Reichstein effects

and Philip S. Hench

1951 Max Theiler Yellow fever and how to combat it

1952 Selman A. Waksman Discovery of streptomycin, the first antibiotic effective againsttuberculosis

1953 Hans Krebs and Discovery of the citric acid cycle and discovery of co-enzymeFritz Lipmann A and its importance for intermediary metabolism

1954 John F. Enders, Thomas Ability of poliomyelitis viruses to grow in cultures of variousH. Weller and Frederick types of tissue

C. Robbins

1955 Hugo Theorell Nature and mode of action of oxidation enzymes

1956 André F. Cournand, Heart catheterization and pathological changes in theWerner Forssmann and circulatory systemDickinson W. Richards

1957 Daniel Bovet Discoveries relating to synthetic compounds that inhibit theaction of certain body substances, and especially their actionon the vascular system and the skeletal muscles

1958 George Beadle, Edward Genes act by regulating definite chemical events (Beadle andTatum, and Joshua Tatum) and discoveries concerning genetic recombination andLederberg the organization of the genetic material of bacteria (Lederberg)

1959 Severo Ochoa and Arthur Mechanisms in the biological synthesis of ribonucleic acidKornberg (RNA) and deoxyribonucleic acid (DNA)

1960 Sir Frank Macfarlane Acquired immunological toleranceBurnet and Peter Medawar

1961 Georg von Békésy Physical mechanism of stimulation within the cochlea

(Contd.)



1962 Francis Crick, James Molecular structure of nucleic acids and its significance forWatson and Maurice Wilkins information transfer in living material

1963 Sir John Eccles, Alan L. Ionic mechanisms involved in excitation and inhibition in theHodgkin and Andrew F. peripheral and central portions of the nerve cell membraneHuxley

1964 Konrad Bloch and Feodor Mechanism and regulation of the cholesterol and fatty acidLynen metabolism

1965 François Jacob, André Genetic control of enzyme and virus synthesis

L woff and Jacques Monod

1966 Peyton Rous and Charles Discovery of tumour inducing viruses (Rous) and discoveriesBrenton Huggins concerning hormonal treatment of prostatic cancer (Huggins)

1967 Ragnar Granit, Haldan K. Primary physiological and chemical visual processes in the eye

Hartline and George Wald

1968 Robert W. Holley, H. Gobind Interpretation of the genetic code and its function in proteinKhorana and Marshall synthesis

W. Nirenberg

1969 Max Delbrück, Alfred D. Replication mechanism and genetic structure of virusesHershey and SalvadorE. Luria

1970 Sir Bernard Katz, Ulf von Humoral transmittors in the nerve terminals and theEuler and Julius Axelrod mechanism for their storage, release and inactivation

1971 Earl W. Sutherland, Jr. Mechanisms of the action of hormones

1972 Gerald M. Edelman and Chemical structure of antibodies

Rodney R. Porter

1973 Karl von Frisch, Konrad Organization and elicitation of individual and social behaviourLorenz and Nikolaas patternsTinbergen

1974 Albert Claude, Christian Structural and functional organization of the cellde Duve and GeorgeE. Palade

1975 David Baltimore, Renato Interaction between tumour viruses and the genetic material

Dulbecco, and Howard of the cell

M. Temin

1976 Baruch S. Blumberg and New mechanisms for the origin and dissemination of

D. Carleton Gajdusek infectious diseases

1977 Roger Guillemin, Andrew V. Discoveries concerning the peptide hormone production ofSchally and Rosalyn Yalow the brain (Roger and Andrew) and for the development of

radioimmunoassays of peptide hormones (Rosalyn)

1978 Werner Arber, Discovery of restriction enzymes and their application toDaniel Nathans and problems of molecular genetics

Hamilton O. Smith

(Contd.)



1979 Allan M. Cormack and Development of computer assisted tomographyGodfrey N. Hounsfield

1980 Baruj Benacerraf, Genetically determined structures on the cell surface thatJean Dausset and regulate immunological reactionsGeorge D. Snell

1981 Roger W. Sperry, David Discoveries concerning the functional specialization of theH.Hubel, Torsten cerebral hemispheres (Roger) and for discoveries concerning

N. Wiesel information processing in the visual system (Hubel and Wiesel)

1982 Sune K. Bergström, Prostaglandins and related biologically active substancesBengt I. Samuelsson and

John R. Vane

1983 Barbara McClintock Discovery of mobile genetic elements

1984 Niels K. Jerne, Georges Theories concerning the specificity in the development andJ.F. Köhler, control of the immune system and the discovery of the principle

César Milstein for production of monoclonal antibodies

1985 Michael S. Brown and Regulation of cholesterol metabolism

Joseph L. Goldstein

1986 Stanley Cohen and Discoveries of growth factors

Rita Levi-Montalcini

1987 Susumu Tonegawa Genetic principle for generation of antibody diversity

1988 Sir James W. Black, Important principles for drug treatmentGertrude B. Elion andGeorge H. Hitchings

1989 J. Michael Bishop and Cellular origin of retroviral oncogenes

Harold E. Varmus

1990 Joseph E. Murray and Organ and cell transplantation in the treatment of humanE. Donnall Thomas disease

1991 Erwin Neher and Bert Function of single ion channel in cellsSakmann

1992 Edmond H. Fischer and Reversible protein phosphorylation as a biological regulatoryEdwin G. Krebs mechanism

1993 Richard J. Roberts and Split genesPhillip A. Sharp

1993 Kary Mullis Invention of the polymerase chain reaction (PCR)

1993 Hamilton Smith Specificity of action of restriction enzymes to splice foreigncomponents into DNA

1994 Alfred G. Gilman and G-proteins and their role in signal transduction in cellMartin Rodbell

1995 Edward B. Lewis, Genetic control of early embryonic developmentChristiane Nüsslein-Volhard andEric F. Wieschaus

(Contd.)



1996 Peter C. Doherty and Rolf Specificity of the cell mediated immune defenceM. Zinkernagel

1997 Stanley B. Prusiner Discovery of prions

1998 Robert F. Furchgott, Louis Nitric oxide as a signaling molecule in the cardiovascular systemJ. Ignarro and Ferid Murad

1999 Günter Blobel Proteins have intrinsic signals that govern their transportand localization in the cell

2000 Arvid Carlsson, Paul Signal transduction in the nervous systemGreengard and EricR. Kandel

2001 Leland H. Hartwell, Tim Key regulators of the cell cycleHunt and Sir Paul Nurse

2002 Sydney Brenner and Genetic regulation of organ development and programmedH. Robert Horvitz and cell deathJohn E. Sulston

2003 Paul C. Lauterbur and Magnetic resonance imaging (MRI)Sir Peter Mansfield

2004 Richard Axel and Linda Odorant receptors and the organization of the olfactory systemB. Buck

2005 Barry J. Marshall and Discovery of the bacterium Helicobacter pylori and its role inJ. Robin Warren gastritis and peptic ulcer disease

2006 Andrew Z. Fire RNA interference, gene silencing by double-stranded RNAand Craig C. Mello

2007 Mario Capecchi, Oliver Gene targeting on knockout mouse using embryonic stem cellsSmithies and Martin Evans and in understanding gene disease relationship

Basic and applied sciences in microbiology

Microbiology, that has played a major role in the advancement of human health and welfare, is oneof the largest and most complex of the biological sciences as it deals with many diverse biologicaldisciplines. In addition to studying the natural history of microbes, it also deals with every aspectof microbe-human and environmental interaction. These interactions include: ecology, genetics,metabolism, infection, disease, chemotherapy, immunology, genetic engineering, industry andagriculture. The branches that come under the large and expanding umbrella of microbiology arecategorized into basic and applied disciplines. The categorization is given below in the Table 1.11.

Table 1.11: Basic and applied disciplines in microbiology

Discipline Nature of study

A. Basic disciplinesAlgology or Phycology Study of algae-simple aquatic organisms ranging from single-celled forms

to large seaweeds.

(Contd.)


Discipline Nature of study

Bacteriology Study of bacteria—the smallest, simplest, single-celled prokaryotic micro-organisms and archaea – prokaryotic microorganisms which constitute anancient group intermediate between the bacteria and eukaryotes.

Mycology Study of fungi – microscopic eukaryotic forms (molds and yeasts), higherforms (mushrooms, toadstools and puffballs), and slime molds.

Protozoology Study of protozoans—animal like and mostly single-celled, eukaryotic organisms.

Virology Study of viruses (infectious agents containing either DNA or RNA that requireliving cells for their replication/ or reproduction) and viral diseases.

Parasitology Study of parasitism and parasites that include pathogenic protozoa, helminthworms and some insects.

Microbial Ecology Study of interrelationships between microbes and environment.

Microbial Morphology Study of detailed structures of microorganisms.

Microbial Systematics Classification, naming, and identification of microorganisms and cons-tructions of the phylogenetic tree of life.

Microbial Physiology Metabolism of microbes at the cellular and molecular levels.

Microbial Biochemistry Study of discovery of microbial enzymes and the chemical reactions carriedout by them.

Molecular Microbiology Study of genome (i.e., genomics) of microorganisms and construction ofphylogenetic tree based on rRNA.

Microbial Genetics Study of heredity and variation in varieties.

Molecular Biology The advanced study of the genetic material (DNA, RNA) and protein synthesis.

B. Applied disciplines

Immunology The immune system that protects against infections and attempts to under-stand the many phenomena that are responsible for both acquired andinnate immunity, in addition to the study of antibody-antigen reactions inthe laboratory.

Agricultural Microbiology Study of relationships of microbes and crops with an emphasis on controlof plant diseases and improvement of yields.

Food Microbiology Interaction of microorganisms and food in relation to food bioprocessing,food spoilage, food borne diseases and their prevention.

Dairy Microbiology Production of and maintenance in quality control of dairy products.

Industrial Microbiology Industrial uses of microbes in the production of alcoholic beverages,vitamins, amino acids, enzymes, antibiotics and other drugs.

Marine Microbiology Study of microorganisms and their activity concerning human and animalhealth in fresh, estuarine and marine waters.

Air Microbiology Role of aerospora in contamination and spoilage of food and disseminationof plant and animal diseases through air.

Exomicrobiology Exploration for microbial life in outer space.

Diagnostic Microbiology Fundamental principles and techniques involved in the study of pathogenicorganisms as well as their application in the diagnosis of infectious diseases.

Epidemiology and Public Monitoring, control and spread of diseases in communities.Health Microbiology

Biotechnology The scientific manipulation of living organisms, especially at the molecularand genetic level to produce useful products.


The new frontiers

The long span of four hundred and fifty years of microbiology has brought amazing insight into thebiology of microorganisms and has also brought with it new challenges, which have both positiveand negative effects upon the society. Diseases like AIDS, Bird’s flu and SARS seem to appear withouta trace and have challenged the basic understanding of microbial diseases. On the other hand, newdiscoveries have opened a door for understanding how a cell works at the most fundamental level,and newly discovered bacteria stretch the already overwhelming picture of microbial diversity.Microbial ecology is providing new clues to the roles of microorganisms in the environment. Biofilmsare recognized as the dominant form of organization of microbial communities. The vast number ofunculturable microbes can be studied and characterized with genomic tools. The understanding ofmicrobial evolution has advanced with the use of genomic technologies and has provided newperspectives on the relationships between microorganisms. Microorganisms play more positive rolesthan simply causing infectious diseases. The majority of microbes are seen as rulers of the worldbecause of their essential and important beneficial roles that can provide humanity with an evenbetter and more healthful existence.

REVIEW QUESTIONS

1. Define microbiology. Enlist the various basic and applied areas of microbiology.

2. Why was the abandonment of the spontaneous generation theory so significant? Using the scientificmethod, describe the steps you would take to test the theory of spontaneous generation.

3. Which early microbiologist was the most responsible for developing sterile laboratory techniques?4. Which scientist is the most responsible for finally laying down the theory of spontaneous generation

to rest?5. Enlist the contributions of Antony van Leeuwenhoek, Edward Jenner, Joseph Lister, Louis Pasteur,

Robert Koch and Joshua Lederberg.6. What are the recent developments in the field of molecular microbiology?7. List important commercial enzymes and their sources.8. Name the scientists who first discovered Archaea?9. What is a binomial system of nomenclature, and who proposed it?

10. Name the causative agents of: syphilis, whooping cough, blastomycosis, tinea cruris, toxoplasmosis,giardiasis and schistosomiasis.

11. What are Koch’s postulates and how did they influence the development of microbiology?12. How did Metchnikoff contribute to the development of immunology?13. Describe the notable contributions of five scientists that resulted in the award of Nobel prizes to

them in microbiology.14. How did Ferdinand Cohn and Carl Woese contribute to bacteriology and molecular biology respectively.15. How did Pasteur’s Swan-neck experiment defeat the theory of spontaneous generation?16. For what contributions are Hooke, Beijerinck, and Ehrlich remembered in microbiology?17. How did the discovery of first antibiotic take place? Name the antibiotic and that mold from which

it was isolated.

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