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MILESTONES IN MICROBIOLOGYBY: DR. NAZIA1ST YEAR POST GRADUATEDEPARTMENT OF MICROBIOLOGY

OBJECTIVES:INTRODUCTIONTHREE PERIODS OF DEVELOPMENT -Pre 1865 period -The Golden Era -Modern Era/Post Golden eraDiscovery of Microbes -Anton van Leeuwenhoek - The Transition Period -Theory of spontaneous generation -Kochs Postulates (the causal relationship between a microorganism and a specific disease) -kochs Molecular Postulates -The Competetion Period

IntroductionMicrobiology is the study of living organisms of microscopic size, which includes bacteria, fungi, algae, protozoa and viruses.It aims to study their form, structure, reproduction, physiology, metabolism and classification.

Microorganisms are closely associated with health and welfare of human beings. Some are beneficial while others are harmful. The science of microbiology did not start until the invention of microscope in 16 th century.

Three periods of developmentI ) Pre 1865 period where there was slow accumulation of facts about bacteria and existence of microbes.

II ) The period between 1865 and 1882 ,also called as Golden Era where the pioneering works of Louis Pasteur ,Robert Koch, Lister etc made the most important discoveries and laid the foundation of microbiology

Modern Era/Post Golden era

III ) The post 1882 period till date, the modern period which has experienced rapid developments in this field due to accumulation of huge knowledge.

Discovery of MicroorganismsEven before microorganisms were seen, some investigators suspected their existence and responsibility for disease.Among others, the Roman philosopher Lucretius (about 9855 B.C.) and the physician Girolamo Fracastoro (14781553) suggested that disease was caused by invisible living creatures.The earliest microscopic observations appear to have been made between 1625 and 1630 on bees and weevils by the Italian Francesco Stelluti, using a microscope probably supplied by Galileo

In 1665, the first drawing of a microorganism was published in Robert Hookes Micrographia.

Discovery Of MicroscopeAntony van leeuwenhoek was the father of microscopy.He was a draper and haberdasher but spent much of his spare time in constructing simple microscope composed of double convex glass lenses held between two silver plates.

Magnification is 50 to 300 times.Liquid specimen is placed between two pieces of glass and shining light on them at 450 angle.This would provide a dark ground illumination

These lens were of pinhead size but would magnify over 200 times.He used these lenses to inspect the quality of cloth. But because of his curiosity he started examining hair fibres , skin scales, blood cells and even samples of his own faeces.At one point he observed tiny sperm cells and speculated that they contain microscopic embryos.

The only scientific group of those times was the Royal Society of London. But the correspondence was tenuos.In 1673, Regnier de Graaf , a fellow of Royal Society urged its members to contact Leeuwenhoek following which they did and he started sending his illustrations and observations.

In september 1674, he filled a glass with greenish cloudy water from a marshy lake outside Delft and observed tiny organisms which he called animalcules.Later he examined materials from his own teeth and faeces and many other materials in which he found these animalcules.

In 1676 Leeuwenhoek sent his 8th letter to the Royal Society. This has special significance as it contains the first description of microorganisims.In 1680 he was elected to fellowship in the Royal Society and he became one of the famous men of his time along with Isaac Newton and Robert Boyle.

A letter to the Royal Society in 1683 included drawings of what are now believed to be bacterial rods , spheres and spiralsHe had sent about 200 letters to the Royal Society

He died at the age of 90 in 1723 (his longevity was an achievement itself).He was a very suspicious and secretive person and invited no one to work with him nor did he show anyone how to grind lenses or construct a microscope .This is one of the reasons why the interest in microorganisms waned after his death.

THE TRANSITION PERIODBiology in 1700s was a body of knowledge without focus.Basically it consisted of observations of plant and animal life and attempts to place the organisms in some logical order.The dominant personality of that era was Carolus Linnaeus a Swedish botanist who brought plants and animals together under one great classification.

In 1718, Louis Jobolt published a review of protozoa.In 1725, Abraham Tremblay described the simple animal known as the hydraThe then scientists could not believe that microorganisms could cause infection.Rather they theorized that infectious diseases were spread by an altered chemical quality of the atmosphere, an entity called the miasma.

Miasma arose from the decaying or diseased bodies known as miasms.The miasma theory figured prominently in medical thinking well into the 1800s.As the years were passing on, some biologists began to scrutinize the laws of nature and question the origin of living things.Then the controversy about spontaneous generation was answered by experimentation

THEORY OF SPONTANEOUS GENERATIONIn the 4th century BC, Aristotle wrote that flies, worms and other animals arise from the decaying matter without the need of parent organisms.This laid the basis for the theory of spontaneous generation (that lifeless substances could give rise to living creatures).

In the early 1600s, the eminent Flemish physician Jan Baptista Van Hemont lent credence to the belief when he observed that rats originate from wheat bran and old rags.Common people also supported his idea as they could also see slime breeding toads and meat generating maggots.

Among the first to dispute this theory was the Florentine scientist Francesco Redi.He reasoned that flies had reproductive organs and suggested that they lay eggs on exposed pieces of meat which then hatch into maggots.In 1670s he attempted to disprove the belief that maggots arise from decaying meat. His work was one of the historys first experiments in biology .

In 1670s he attempted to disprove the belief that maggots arise from decaying meat. His work was one of the historys first experiments in biology .

An Italian cleric and scientist, Abbe Lazzaro Spallanzi criticized Needhams work.He boiled meat and vegetable broths for long periods and then sealed the necks of the flasks by melting the glass.As a control he left some flasks open to air, stoppered some loosely with corks and boiled some briefly.

After 2 days he found the control flasks swarming with microorganisms but the sealed flasks had none.His work was countered again by Needham saying that he had destroyed the vital force of life with excessive heat, and a few others opined that air necessary for life has been excluded.The controversy over this theory of spontaneous generation continued which encouraged scientists to experiment in biology

While the debate on spontaneous generation continued, a few scientists studied on how diseases were transmitted.In 1546, an Italian poet and scientist Girolamo Fracastoro wrote cotagion is an infection that passes from one thing to another.He recognized 3 froms of passage contact, air and lifeless objects.His ideas were later interwoven by the miasma theory and was given little credibility.

Athanasius Kirker reported microscopic worms in the blood of plague victims- which was not considered as other scientists thought that what he had seen were only blood cells.Nor was Christian Fabricius taken seriously when he suggested that fungi cause rust and smut disease in plants in 1700s.

On the contrary Edward Jenner received many accolades when he discovered immunization for smallpox in the year 1798, though he could not explain the cause of the disease.In the 1700s small pox was so rampant in England and Europe that 1/3rd of the children died before reaching the age of 3.Many were blinded and most were left pockmarked for life.

But those who have survived an attack of small pox were immune for life.Thus the people started contracting a mild form of disease where a doctor would make a small wound in the arm and insert a few drops of pus from a small pox skin lesion.Though mild form of the disease would develop and the patients were resistant for life, there were also cases of severe form of the disease.

Edward Jenner (a country surgeon) in 1700s who learned that people who experienced cowpox were apparently immune to smallpox.In 1796, a dairy maid named Sarah Nelmes came to his office who had lesions of cowpox on her hand.Jenner took material from her hand and scratched it into the skin of a boy named James Phipps.

Few weeks later he inoculated Phipps with material from a small pox lesion.Within days the boy developed a reaction at the site but failed to show any sign of small pox.During the course of his experiments he obtained cowpox material from cows

In 1798 he published a historic pamphlet in which he gave a description about his method of preventing the fatal disease.Many physicians confirmed his findings and within a few years his method of vaccination (vacca = cow) spread through the world.By 1801 about 1lakh people in England were vaccinated.Jenners experiments and interpretations of vaccination served well as models for accurate and careful laboratory work in modern microbiology

The first clear reference to smallpox inoculation was made by theChineseauthor Wan Quan (14991582) in hisDouzhen xinfa published in 1549.Inoculation for smallpox does not appear to have been widespread in China until the reign era of theLongqing Emperor(15671572) during theMing Dynasty.

In China powdered smallpox scabs were blown up the noses of the healthy. The patients would then develop a mild case of the disease and from then on were immune to it. The technique did have a 0.5-2% mortality rate, but that was considerably less than the 20-30% mortality rate of the disease itself.

By the mid 1800s enough knowledge had accumulated to convince physicians that diseases could be contagious and that transmission could be interrupted.Oliver Wendell Holmes (1843) in the USA and Ignaz Semmelweiss in Vienna (1846) had independently concluded that puerperal sepsis was contagious.

Semmelweis a Hungarian physician in 1847 reported that the agent of blood poisoning was transmitted to maternity patients by physicians fresh from performing autopsies in the mortuary.He showed that hand washing in chlorine water could stop the spread of the disease.But he was considered insane.

John Snow a British physician traced the source of cholera to the municipal water supply of London during an 1854 outbreak.He reasoned that by avoiding the contaminated water source, people could avoid the disease.Thus both Semmelweis and Snow disproved the theory of miasma and concluded that a poison or unknown substance was responsible for disease.

The first discovery of a pathogenic microorganism was probably made by Agostino Bassi (1835) who showed that the muscaridine disease of silkworms was caused by a fungus.

THE GOLDEN AGE OF MICROBIOLOGY (1857- 1914)

Microbiology blossomed during this period, thus referred to as the golden age of microbiology.During these years, numerous branches of microbiology were established and the foundations were laid for the maturing process that has led to the modern microbiology.

LOUIS PASTEUR (1822-1895)

The French chemist whose experiments on germs led to the greatest medical breakthrough of all time.Born on dec 27th 1822 in Dole, France.Studied at a French school, The Ecole Normale Superieure.In 1848 he achieved distinction in organic chemistry for his discovery that tartaric acid, a four carbon compound forms two different types of crystals.

Using microscope he successfully separated the crystals and developed a skill that aided his later studies of microorganisms.He was appointed as professor of chemistry at the University of Lille in Northern France in 1854.In 1857 he developed curiosity as to why the local wines were turning sour

In a series of experiments he clarified the role of yeast cells in fermentation and that the bacteria were responsible for sour wine.First he removed all the traces of yeast from a flask of grape juice and set the juice aside to ferment and he observed that nothing happened.Then he added back the yeasts and soon found that the fermentation was proceeding normally.

In a series of experiments he clarified the role of yeast cells in fermentation and that the bacteria were responsible for sour wine.First he removed all the traces of yeast from a flask of grape juice and set the juice aside to ferment and he observed that nothing happened.Then he added back the yeasts and soon found that the fermentation was proceeding normally.

In 1857, he published a short paper on souring by bacteria and also implied that the microorganisms were related to human illness and set down the foundation for the germ theory of disease.This theory holds that microorganisms are responsible for infectious diseases.

He also recommended a practical solution to the sour wine problem.He suggested that grape juice be heated to destroy all the evidence of life , after which yeast should be added to begin fermentation.An alternative was to heat the wine after fermentation , before ageing so that souring is prevented.This technique was accepted and ended the problem and was named pasteurization.

Pasteurs interest in micro organisms rose as he learned more about them.He found bacteria in soil , water , air and the blood of diseased victims

Extending his germ theory of disease, he reasoned that if microorganisms were acquiring from the environment, their spread can be controlled.Thus the chain of transmission could be broken.However many scientists stubbornly stuck to the notion that bacteria arise spontaneously from organic matter and the disease is inevitable.

He wanted to prove his germ theory and disprove the theory of spontaneous generation and conducted a series of experiments.He first showed that where diseases were rampant, the air was full of microorganisms, but where disease was uncommon the air was clean.

He opened flasks of nutrient rich broth to air from the crowded city, then from the country side and from the high mountain.In each succeeding experiment fewer flasks became contaminated with microorganisms.When he boiled the broths they remained free of life and the critics argued that boiling destroyed the life force which is believed to be in the air.

Finally in a series of experiments Pasteur silenced almost all the supporters of the theory of spontaneous generation.Pasteur brought an end to the long debate on spontaneous generation.

Pasteur then realized that he was no closer to solve the riddle of disease.In the year 1865 cholera struck Paris killing 200 people a day when Pasteur attempted to capture the responsible bacteria by filtering the hospital air and trapping the bacteria in cotton.But he was unable to cultivate one bacterium apart from the others because he was using the broth.

Later Pasteur demonstrated that bacterial inoculations made animals ill but could not pin point the exact cause.Some of his critics then claimed that a poison or toxin in the broth was responsible for the disease.In an effort to help the French industry Pasteur turned his attention to pebrine the disease of silk worms

Late in 1865, he identified a protozoan infesting the silk worms and the mulberry leaves fed to them.Next he separated the healthy silk worms from the diseased ones and also their food. Thus he managed to control the spread of disease.It was a time of grief again as his 3rd daughter Cecille died of typhoid in the year 1872 following which he returned to the study of human disease

Although Pasteur failed to relate a specific organism to a specific human disease his work stimulated others to investigate the nature of microorganisms and to ponder their association with disease

Gerhard Hansen a Norwegian physician identified bacteria in the tissues of leprosy patients in the year 1871.

OttoObermeier the founder of German parasitology and father of German tropical medicine described bacteria in the blood of relapsing fever patients in 1873.Another German bacterologist Ferdinand J. Cohn discovered that bacteria multiply by dividing into two cells.

In England Joseph Lister (1869) introduced the antiseptic technique in surgery after being impressed by Pasteurs work.

This helped in the effective drop in the morbidity and mortality due to surgical sepsis.His views of carbolic acid was hazardous and cumbersome.That was a milestone in the evolution of antiseptic surgery ( father of antiseptic surgery)

ROBERT KOCH (1843-1910)

A country doctor from East Prussia who wanted to be an explorer ,was frustrated by his inability to do anything to cure disease.Kochs primary interest was anthrax, a deadly blood disease in cattle and sheep.In the year 1875, in his laboratory he injected mice with the blood of diseased sheep and cattleHe then found that the mice developed same symptoms as those of sheep and cattle.

Then he isolated a few rod shaped bacteria from the blood into sterile aqueous humor of oxs eye.He watched for hours as the bacilli multiplied, formed tangles and finally formed spores.These spores were injected into healthy mice and the symptoms of anthrax developed within a few hours.

POSTULATEExperimentationThe microorganism must be present in every case of the disease but absent from healthy organisms.Koch developed a staining technique to examine human tissue. M. tuberculosiscells could be identified in diseased tissue. The suspected microorganisms must be isolated and grown in a pure cultureKoch grew M. tuberculosis in pure culture on coagulated blood serum. The same disease must result when the isolated microorganism is inoculated into a healthy hostKoch injected cells from the pure culture of M.tuberculosis into guinea pigs. The guinea pigs subsequently died of tuberculosisThe same microorganism must be isolated again from the diseased hostKoch isolated M. tuberculosis from the dead guinea pigs and wasable to again culture the microbe in pure culture on coagulated blood serum.

EXCEPTIONS TO KOCHS POSTULATESSome microbes are obligate intracellular parasites (like chlamydia or viruses) and are very challenging, or even impossible, to grow on artificial media.Some diseases, such as tetanus, have variable signs and symptoms between patients.Some diseases, such as pneumonia & nephritis, may be caused by a variety of microbes.Some pathogens, such as S. pyogenes, cause several different diseases.Certain pathogens, such as HIV, cause disease in humans only it is unethical to purposefully infect a human.

Following this achievement Koch developed various staining techniques for bacteria.Then he happened to develop various culture methods of bacteria.He observed that a slice of potato contained small masses of bacteria which he termed colonies.

Seeing that bacteria could grow and multiply on solid surfaces, Koch added gelatin to his broth to prepare a solid culture medium.He found visible colonies over the surface of the solid medium after a day after inoculation.Thus he could isolate pure cultures of bacteria and was certain that only one species of bacterium was involved in disease.

Thus his work proved that bacteria but not the toxins in the broth were the cause of the disease.This was one of the greatest achievements in the field of microbiology.One of the drawbacks of his gelatin culture medium was that a few bacteria were digesting gelatin and also at high temperatures it gets liquified.

Then Fannie Hesse, wife of Kochs associates suggested the use of agar ( a sea weed derived powder) for solidification of culture media as she observed her mom using it for preparing jams and jellies.Agar did not liquify even at high temperatures and mixed well with almost all liquids.In 1881 Koch demonstrated his pure culture techniques to the international medical congress in London at Listers laboratory.

kochs Molecular Postulates

Although the criteria that Koch developed for proving a causal relationship between a microorganism and a specific disease have been of great importance in medical microbiology, it is not always possible to apply them in studying human diseases. For example, some pathogens cannot be grown in pure culture outside the host; because other pathogens grow only in humans, their study would require experimentation on people. The identification, isolation, and cloning of genes responsible for pathogen virulence have made possible a new molecular form of Kochs postulates that resolves some of these difficulties. The emphasis is on the virulence genes present in the infectious agent rather than on the agent itself. The molecular postulates can be briefly summarized as follows

1. The virulence trait under study should be associated much more with pathogenic strains of the species than with nonpathogenic strains 2. Inactivation of the gene or genes associated with the suspected virulence trait should substantially decrease pathogenicity. 3. Replacement of the mutated gene with the normal wild-type gene should fully restore pathogenicity. 4. The gene should be expressed at some point during the infection and disease process. 5. Antibodies or immune system cells directed against the gene products should protect the host.

The molecular approach cannot always be applied because of problems such as the lack of an appropriate animal system. It also is difficult to employ the molecular postulates when the pathogen is not well characterized genetically.

THE COMPETITION PERIODKochs verification of germ theory was presented in 1876 and within 2 years Pasteur had verified the proof and went a step ahead stating that bacteria were temperature sensitive because chickens did not acquire anthrax at their normal body temperature of 42 c but did so when they were cooled down to 37 c.

Pasteur also recovered anthrax spores from the soil and suggested that dead animals can be burned or buried deeply in soil unfit for grazing.During the course of Pasteurs study he introduced techniques of sterilization and developed steam sterilizer, autoclave and hot air oven.

He also established the differing growth needs of different bacteria.One of Pasteurs remarkable discoveries was made in 1880.An accidental observation that chicken cholera bacillus cultures left on the bench for several weeks lost their pathogenic ability but retained their ability to protect the birds against subsequent infection by them.

This observation led to the discovery of the process of attenuation and the development of vaccines.He attenuated the cultures of anthrax bacillus by incubation at high temperatures and proved that inoculation of such cultures in animals induced specific protection against anthrax and was successful by demonstrating it in a public experiment in the year 1881.

It was Pasteur who coined the term vaccine.Koch in Germany in 1881 isolated the bacillus that causes tuberculosis.In 1884 his associate George Gaffky cultivated the typhoid bacillus.In the same year, another associate of his Friedrich Loeffler isolated diphtheria bacillus.

Emile Roux and Alexandre Yersin of Pasteurs group had linked diphtheria to a toxin produced in the body.Kochs coworker Emil Von Behring successfully treated diphtheria by injecting antitoxin- a preparation of antibodies obtained from animals immunized against diphtheria for which he was awarded the first nobel prize of physiology and medicine.

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 Pasteurs associates Elie Metchinkoff a native of Ukraine in 1884 published an account of phagocytosis, a defensive process in which the WBCs engulf and destroy microorganisms.

Ernst Karl Abbe a German physicist introduced the oil immersion lens of the microscope in the year 1878.8 years later he invented the system of lenses and mirrors known as Abbe condenser which concentrates light on objects being viewed and makes increased magnification feasible.

In 1885 Pasteur successfully immunized young Joseph Meister against the dreaded disease rabies . Although he never saw the agent causing rabies he could cultivate it in the brain of animals and inject the boy with bits of the brain tissue.Many monetary rewards followed after this discovery and after immunization of 20 peasants against rabies .

These funds helped him establish The Pasteur Institute in Paris, one of the worlds foremost scientific establishments.Pasteur presided over it till his death in 1895.In 1883, Robert Koch studied cholera in Egypt and India and could isolate a comma shaped bacillus and confirmed the suspicion raised by John Snow that water is the key to transmission

In 1891,he became the director of Berlins Institute of Infectious Diseases.He studied about malaria, plague and sleeping sickness. But his work with tuberculosis ultimately gained him the nobel prize in physiology or medicine in 1905.He died of stroke in 1910 at the age of 66.

OTHER PIONEERS IN THE GOLDEN AGE

Charles Nicolle of Pasteur Institute proved that typhus fever was transmitted by lice.

Albert Calmette of Pasteur Institute developed a harmless strain of tubercle bacillus use for immunization.

A French scientist Jules Bordet isolated the bacillus of pertusis or whooping cough

Kochs successors Emil Von Behring and Richard Pfeiffer isolated one of the several organisms causing meningitis

Another coworker Paul Ehrlich a chemist explored the mechanisms of immunity and synthesized the magic bullet an arsenic compound that would seek out and destroy syphilis organisms in the human body.

Sir Ronald Ross an English physician proved that mosquitoes are the vital link in the transmission of malaria and was awarded the nobel prize in 1902.

David Bruce showed that tse tse flies transmit sleeping sickness.A british scientist Almroth Wright described opsonins, the chemical substances that assist phagocytosis in the body.

William Welch isolated the gas gangrene bacillus.

A Russian scientist Sergius Winogradsky discovered that certain bacteria utilize carbon dioxide to synthesize carbohydrates similar to plants.

And many more discoveries were made the fields of virology, mycology, parasitology and immunology.The advent of world war I in 1914 signalled the end of the golden age of microbiology.

Individual bacteria and their discoveries

STAPHYLOCOCCIVon Recklinghausen (1871)

Pasteur (1880)

Observed Staphylococci in human pyogenic lesions.Obtained liquid cultures of the cocci from pus and produced abscesses by inoculating them into rabbits.

Sir Alexander Ogston (Scottish surgeon in 1880)

Established the causative role of the coccus in abscesses and other suppurative lesions.Gave the name Staphyococcus Noticed non virulent Staphylococci on skin surfaces.

Rosenbach (1886)

Kitasato (1889) Demonstrated a slender bacillus with round terminal spores in a case of tetanus.

Demonstrated the etiological role of the bacillus in tetanus and isolated it in pure culture and reproduced the disease in animals by inoculation of pure cultures.

STREPTOCOCCIBillroth (1874)

Ogston (1881)First to see cocci in chains in erysipelas and wound infection.Gave the name Streptococci.

Isolated them from acute abscesses.

Escherich (1885)

Friedlander (1883)Escherichia coli was named after him who was the first to describe the colon bacillus.

Klebsiella pneumoniae was first isolated by him from fatal cases of pneumonia.

PNEUMOCOCCIPasteur (1881) and Sternberg (1881)

Fraenkel and Weichselbaum (1886)First noticed them and produced fatal septicemia in rabbits by inoculating human saliva and isolated pneumococci from the blood of animals.Established the relationship between Pneumococci and pneumonia

NEISSERIANeisser (1879)

Weichselbaum (1887)First described N. gonorrhea in pus in gonorrheal patients.

First described N. meningtidis and isolated it from spinal fluid of a patient.

CORYNRBACTERIUM Bretonneau (1826)

Klebs (1883)

Loeffler (1884)First recognised diphtheria as a clinical entity and called the organism as diphtherite.First observed and described the bacillus.First cultivated the bacillus.

Roux and Yersin (1888)

Von Behring (1890)Discovered the diphtheria exotoxin and established its pathogenic effect.

First described the exotoxin.

BACILLUS ANTHRACISPollender (1849)

Davaine (1850)First pathogenic bacterium to be observed under the microscope.The first communicable disease shown to be transmitted by inoculating infected blood

Robert Koch (1876)

Pasteur (1881)First bacillus to be isolated in pure cultures and shown to possess spores .

First bacterium used for the preparation of attenuated vaccine.

CLOSTRIDIUM

Achalme (1891)

Welch and Nuttall (1892)

First cultivated Cl. perfringensIsolated from the blood and organs of cadaver.

CLOSTRIDIUM TETANIHippocrates and AretaeusCarle and Rattone (1884)Nicolaier (1884)Described since ancient times.Transmitted the disease to rabbits.Suggested that the manifestations of the disease were due to a strychnine like poison produced by the bacillus.

Shiga (1896)

Eberth (1880)

Gaffky (1884)Isolated Shigella from an epidemic dysentery in Japan. First observed salmonella in mesenteric nodes.First isolated from a case of typhoid.

Pacini (1854)

Robert Koch(1883)

Yersin and Kitasato (1894)First observed Vibrio cholera.First isolated from cholera patients.

Plague bacillus was discovered simultaneously.

Pfeiffer (1892)Observed Haemophilus in the sputum of the patients from an influenza pandemic but no causal relationship was proven later by Smith and Andrews.

Jules Bordet and Gengou (1900)

David Bruce(1886)

Identified Bordetella pertussis in sputum of cases of whooping cough and succesfully cultivated it.Isolated Brucella from the spleen of fatal cases of malta fever.

Robert Koch (1882)

Hansen (1868)

Schaudinn and Hoffman (1905)

Isolated the human Tubercle bacillus.Discovered the lepra bacillus .

Discovered the causative agent of syphilis Treponema pallidum.

Wolff and Israel (1891)Warren and Marshall (1983)

Isolated actinomycetes.Observed H.pylori in cases of gastritis and peptic ulcer.

REFERENCESPrescott, Harley, and Kleins Microbiology 7th editionALCAMO Fundamentals Of Microbiology, 6th edition.Ananthanarayan and Panikers Textbook of Microbiology, 9th editionInternet

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