Section 1
General Bacteriology
LEARNING OBJECTIVES
- • Contributions of Antony van Leeuwenhoek
- • Contributions of Louis Pasteur
- • Contributions of Robert Koch
- • Koch's postulates
- • Contributions of Paul Ehrlich.
INTRODUCTION
Microbiology is the study of living organisms of microscopic size. Medical microbiology is the subdivision concerned with the causative agents of infectious disease of man, the response of the host to infection and various methods of diagnosis, treatment and prevention.
INFECTION AND CONTAGION
Concept of contagion: Long before microbes had been seen, observations on communicable diseases had given rise to the concept of contagion: the spread of disease by contact, direct or indirect. This idea was implicit in the laws enacted in early biblical times to prevent the spread of leprosy.
Invisible living creatures produced disease: Varro in the 2nd century BC later recorded the principle of contagion by invisible creatures. Roger Bacon, in the 13th century, more than a millennium later, postulated that invisible living creatures produced disease. Fracastorius (1546), a physician of Verona, concluded that communicable diseases were caused by living agents (germs) ‘seminaria’ or ‘seeds’. Kircher (1659) reported finding minute worms in the blood of plague victims, but with the equipment available to him, it is more likely that what he observed were only blood cells.
DISCOVERY OF MICROORGANISMS
As microbes are invisible to the unaided eye, direct observation of microorganisms had to await the development of the microscope.
Antony van Leeuwenhoek (1632–1723)
The credit for having first observed and reported bacteria belongs to Antony van Leeuwenhoek. Antony van Leeuwenhoek, the Dutchman, was a draper and haberdasher in Delft, Holland. His hobby was grinding lenses and observing diverse materials through them. He was the first person to observe microorganisms (1673) using a simple microscope. In 1683, he made accurate descriptions of various types of bacteria and communicated them to the Royal Society of London. He recognized them as living creatures (animalcules) and to Leeuwenhoek the world of ‘little animalcules’ represented only a curiosity of nature. Their importance in medicine and in other areas of biology came to be recognized two centuries later.
Contributions of Antony van Leeuwenhoek
- He constructed the first microscope.
- The first person to observe microorganisms (1673).
- Provided accurate description of bacteria.
CONFLICT OVER SPONTANEOUS GENERATION
Spontaneous Generation (Abiogenesis)
John Needham (1713–1781), the English priest in 1745 published experiments purporting the spontaneous generation (abiogenesis) of microorganisms in putrescible fluids. Lazzaro Spallanzani (1729–1799), an Italian priest and naturalist opposed this view who boiled beef broth for an hour, sealed the flasks, and observed no 2 formation of microbes. Franz Schulze (1815–1873), Theodore Schwann (1810–1882), Georg Friedrich Schroder and Theodor von Dusch attempted to counter such arguments. Louis Pasteur of proved conclusively that all forms of life, even microbes, arose only from their like and not de novo.
John Tyndall (1820–1893), the English physicist finally in 1877 proved and was able to explain satisfactorily the need for prolonged heating to eliminate microbial life from infusions. Intermittent heating, now called tyndallization, killed both heat-stable form and a heat-sensitive form of bacteria.
ROLE OF MICROORGANISMS IN DISEASES
Augustino Bassi (1773–1856) demonstrated in 1835 that a silkworm disease called ‘muscardine’ was due to a fungal infection. MJ Berkeley (1845) proved that the great potato blight of Ireland was caused by a fungus. Following his success with the study of fermentation, Pasteur imeestigated the pebrine disease of silueosm.
Indirect transmission was recognized in the 1840s, when American poet-physician Oliver Wendell Holmes (1843) in Boston, USA and Ignaz Semmelweis in Vienna (1846) had independently concluded that puerperal sepsis was contagious. Semmelweis also identified its mode of transmission by doctors and medical students attending on women in labor in the hospital and had prevented it by the simple measure of washing hands in an antiseptic solution. Semmelweis was persecuted by medical orthodoxy and driven insane for the service to medicine and humanity.
SCIENTIFIC DEVELOPMENT OF MICROBIOLOGY
The development of microbiology as a scientific discipline dates from Louis Pasteur, perfection on microbiological studies by Robert Koch, the introduction of antiseptic surgery by Lord Lister and contributions of Paul Ehrlich in chemotherapy.
LOUIS PASTEUR (1822–1895)
Louis Pasteur (1822–1895) (Fig. 1.1) was born in the village of Dole, France on December 27, 1822, the son of humble parents. His father was a tanner. He was originally trained as a chemist, but his studies on fermentation led him to take interest in micro-organisms. His discoveries revolutionized medical practice, although he never studied medicine.
Louis Pasteur (Fig. 1.1) is known as ‘Father of Microbiology’ because his contribution led to the development of microbiology as a separate scientific discipline.
Contributions of Louis Pasteur in Microbiology (Box 1.1)
- Coined the term ‘Microbiology’: For the study of living organnisms of microscopic size.
- Proposed germ theory of disease: He established that putrefaction and fermentation was the result of microbial activity and that different types of fermentations were associated with different types of microoganisms (1857).
- Disapproved theory of spontaneous generation: He disapproved the theory of spontaneous generation in 1860–1861 in public controversy with Pouchet who was a proponent of spontaneous generation. In a series of classic experiments in the swan-necked flasks, Pasteur proved conclusively by demonstrating the the ubiquity of microorganisms that all forms of life, even microbes, arose only from their like and not de novo.
- Developed sterilization techniques and developed the steam sterilizer, hot-air oven and autoclave in the course of these studies.
- Developed methods and techniques for cultivation of microorganisms.
- Studies on pebrine (silkworm disease), anthrax, chicken cholera and hydrophobia.
- Pasteurization: He deviced the process of destroying bacteria, known as pasteurization.
- Coined the term ‘Vaccine’: It was Pasteur who coined the term vaccine for such prophylactic preparations.
- Discovery of the process of attenuation and chicken cholera vaccine: An accidental observation that chicken cholera bacillus cultures left on the bench for several weeks lost their pathogenic property but retained their ability to protect the birds against subsequent infection by them, led to the discovery of the process of attenuation and the development of live vaccines.
- Developed live attenuated anthrax vaccine: He attenuated cultures of the anthrax bacillus by incubation at high temperature (42–43°C) and proved that inoculation of such cultures in animals induced specific protection against anthrax. The success of such immunization was dramatically demonstrated by a public experiment on a farm at Pouilly-le-Fort (1881) during which vaccinated sheep, goats and cows were challenged with a virulent anthrax bacillus culture. All the vaccinated animals survived the challenge, while an equal number of unvaccinated control animals succumbed to it.
- Noticed pneumococci: Pneumococci were first noticed by Pasteur and Sternberg independently in 1881.
JOSEPH LISTER (1827–1912)
Joseph Lister was a professor of Surgery in Glasgo Royal Infirmary. He applied Pasteur's work and introduced antiseptic techniques in surgery (1867). The approach was remarkably successful effecting a pronounced drop in mortality and morbidity due to surgical sepsis. He established the guiding principle of antisepsis for good surgical practice. Lister antiseptic surgery innvolved carbolic acid and was cumbersome and hazardous but was a milestone in the evolution of surgical practice from the era of ‘laudable pus’ to modern aseptic techniques. For this work, he is called the ‘Father of Modern Surgery’.
ROBERT KOCH (1843–1910) (FIG. 1.2)
Robert Koch (Fig. 1.2) was a German physician. The first direct demonstration of the role of bacteria in carrying the disease came by the study of anthrax by Koch. Winner of the Nobel Prize in 1905, Robert Koch is known as ‘Father of Bacteriology’.
Contributions of Robert Koch
- Staining techniqes: He described methods for the easy microscopic examination of bacteria (1877).
- Hanging drop method: He was the first to use hanging drop method by studying bacterial motility.
- He deviced a simple method for isolating pure cultures of bacteria by plating out mixed material on a solid culture medium.
- Discoveries of the causal agents of anthrax (1876), tuberculosis (1882) and cholera (1883).
- Koch's postulates: His criteria for proving the causal relationship between a microorganism and a specific disease are known as Koch's postulates.
- Koch's phenomenon: Koch (1890) observed that a guinea pig already infected with the tubercle bacillus responded with an exaggerated expresssion when injected with the tubercle bacillus or its protein. This hypersensitivity reaction is known as Koch's phenomenon.
Important discoveries by other scientists: Hansen (1874) described the leprosy bacillus; Neisser (1879) discovered the gonococcus; Eberth (1880) observed the typhoid bacillus; Alexander Ogston (1881) described the staphylococci; Loeffler (1884) described the diphtheria bacillus; Nicolaier (1884) observed the tetanus bacillus; Rosenbach (1886) demonstrated the tetanus bacillus; Fraenkel (1886) described the pneumococcus; in 1887, Weichselbakum described and isolated the meningococcus; in 1887 Bruce identified the causative agent of malta fever; in 1905 Schaudin and Hoffman discovered the syphilis.
PAUL EHRLICH (1854–1915)
Paul Ehrlich was an outstanding German Scientist and genius of extraordinary activity. He was also known as the ‘Father of Chemotherapy’.
Contributions of Paul Ehrlich
- Applied stains to cells and tissues for the purpose of revealing their functions.
- Introduced methods of standardizing toxin and antitoxin
- Proposed ‘side chain theory’ of antibody production
- Salvarsan introduction: He introduced salvarsan, an arsenical compound, sometimes called the ‘magic bullet’. It was capable of destroying the spirochaete of syphilis. Later on, he discovered neosalvarsan. Thus, he created a new branch of medicine known as chemotherapy.
DISCOVERY OF VIRUSES
As a science, virology evolved later than bacteriology. Although the physical nature of viruses was not fully revealed until the invention of the electron microscope, the infections they cause have been known and feared since the dawn of history.
- Infectious Agents Smaller than BacteriaThe infectious agents of numerous diseases were being isolated and many infectious diseases had been proved to be caused by bacteria. But there remained a large number of diseases for which no bacterial cause could be established until it was realized that the responsible agents were smaller than bacteria.
- Various Infections
- Rabies in dogs: Pasteur had suspected that rabies in dogs could be caused by a microbe too small to be seen under the microscope.
- Tobacco mosaic disease: Iwanowski (1892), Russian scientist and Martinus Beijrinck (1898) in Holland attributed the cause of tobacco—mosaic disease to the infectious agents in bacteria-free filtrates to be living but fluidcontagium vivum fluidum and introduced the term virus (Latin for ‘poison’) for such filterable infectious agents.
- Foot-and-mouth disease of cattle: Friedrich Loeffler and Paul Frosch at the same time in 1898 in Germany found that foot-and-mouth disease of cattle was also caused by a similar filter-passing virus.
- Yellow fever: The discovery of first human disease proved to have a viral etiology was yellow fever. The US Army Yellow Fever Commission under Walter Reed in Cuba (1902) showed that this human disease (yellow fever) was not only a filterable virus but also transmitted through the bite of infected mosquitoes.
- Electron microscope: Viruses could not be visualized under the light microscope or grown in culture media. So investigation of viruses and the disease caused by them were rendered difficult. Larger viruses could be seen under light microscope after appropriate staining but their detailed morphology could only be studied by electron microscope by Ruska (1934).
- Cultivation of virusesThe technique of growing them on chick embryos was developed by Goodpasture in 1930s. The use of living human and animal tissue cells for the in-vitro culture of viruses was developed by John Enders (1949) and others.
- Virus infection and malignancy
- Leukemia: Vilhelm Ellerman and Oluf Bang (1908) in Copenhagen put forth the possibility that virus infection could lead to malignancy.
- Sarcoma in fowls: Peyton Rous (1911) three years later isolated a virus causing sarcoma in fowls. Several viruses have been blamed to cause natural and experimental tumors in birds and animals. Viruses also cause malignant transformation of the infected cells in tissue culture.
- Viral oncogenesis: The discovery of viral and cellular oncogenes have put forth the possible mechanisms of viral oncogenesis. Positive proof of a virus causing human malignancy was established when the virus of human T-cell leukemia was isolated in 1980.
- Bacteriophages: Frederick W Twort (1915) and Felix D Herelle (1917) independently discovered a lytic phenomenon in bacterial cultures. The agents responsible were termed bacteriophages (viruses that attack bacteria).
IMMUNITY AND IMMUNIZATION
- Ancient knowledgeThe practice of producing a mild form of smallpox intentionally (variolation) was prevalent in India, China and other ancient civilizations from time immemorial.
- Edward Jenner (1749–1823)The first scientific attempts at artificial immunizations in the late eighteenth century were made by Edward Jenner (1749–1823) from England. He introduced the technique of vaccination using a related but mild live virus of cowpox (1796). Edward Jenner is known as the ‘Father of Immunology’.
- Live vaccinesFurther work on immunization was carried out by Louis Pasteur and derived attenuated (reduced in virulence) live vaccines for fowl cholera, anthrax, swine erysipelas and rabies.
- Vaccine for hydrophobiaPasteur's development of a vaccine for hydrophobia made the greatest impact in medicine. This was acclaimed throughout the world.
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Nuttal (1888) observed that defibrinated blood had a bactericidal effect and Buchner (1889) noticed that this effect was abolished by heating the sera for one hour at 55°C. This heat-labile bactericidal factor was termed ‘alexine’. The first step in elucidating the mechanisms of acquired immunity was the discovery of antibodies by Emil von Behring and Shibasaburo Kitasato (1890) in the sera of animals which had received sublethal dose of diphtheria or tetanus toxoid. Pfeiffer (1893) demonstrated bactericidal effect in vivo by injecting live cholera vibrios intraperitoneally in guinea pigs previously injected with killed vibrios. Bordet (1895) defined two components in this reaction, the first being heat stable substance ‘antibody’ found in the immune sera and the second being heat labile subsequently named ‘complement’.
- Cellular concept of immunityElie Metchnikoff (1883) discovered the phenomenon of phagocytosis and developed the cellular concept of immunity. Paul Ehrlich hypothesized that immunity could be explained by the presence of noncellular components of blood. Wright (1903) discovered opsonization. Both Metchnikoff and Ehrlich shared a Nobel Prize in 1908 for their contributions to the emerging science of immunology. The pioneering work of Landsteiner laid the foundation of immunochemistry.
- AllergyAnaphylaxis—Portier and Richet (1902), studying the effect of the toxic extracts of sea anemones in dogs, made the paradoxical observation that dogs which had prior contact with the toxin were abnormally sensitive to even minute quantities of it subsequently. This phenomenon was termed anaphylaxis.
- Selection theory of antibodyIn 1955, Jerne proposed the ‘natural selection theory’ of antibody synthesis. Burnet (1957) modified this into clonal selection theory.
- Immunological surveillanceBurnet (1967) developed the concept of immunological surveillance based on the original suggestion of Thomas (1959). Malignancy was thought to be a failure of this function.
- TransplantationUnderstanding of the immunological basis of transplantation, largely due to the work of Medawar and Burnet.
SEROTHERAPY AND CHEMOTHERAPY
Antisera: The work of Behring and Kitasato led to the successful use of antisera raised in animals for the treatment of patients with diphtheria, tetanus, pneumonia and other diseases.
Magic bullet: Ehrlich (1909) discovered salvarsan (arsenaphenamine), sometimes called the ‘magic bullet’, was capable of destroying the spirochaete of syphilis. In 1912, he discovered neosalvarsan. This gave him the title, ‘Father of Chemotherapy’.
Antibiotics—A Fotunate Accident
The modern era of antibiotics developed only after Gerhard Domagk (1895–1964) found that prontosil (the forerunner of sulfonamides) had a dramatic effect on streptococcal infection in 1935. Sir Alexander Fleming (1881–1955) made accidental discovery that the fungus Penicillium notatum produces a substance which destroys staphylococci. In the 1940s, Florey and Chain and their associates demonstrates its clinical value. This was the beginning of the antibiotics era. Selman Waksman exploited the potential for antibiotic production among the soil microorganisms in the 1940s.
NOBEL PRIZES AWARDED FOR RESEARCH IN MICROBIOLOGY
The number of Nobel laureates in Medicine and Physiology for their contribution in microbiology is an evidence of the positive contribution made to human health by the science of microbiology. About one-third of these have been awarded to scientists working on microbiological problems (Table 1.1).
IMPORTANT QUESTION
Write short notes on:
- Contributions of Antony van Leeuwenhoek
- Contributions of Louis Pasteur
- Contributions of Robert Koch
- Koch's postulates
- Contributions of Edward Jenner
- Contributions of Paul Ehrlich
- Name four Nobel laureates in Microbiology
MULTIPLE CHOICE QUESTIONS (MCQS)
1. Who was the first person to describe micro-organisms ?
- Louis Pasteur
- Robert Koch
- Paul Ehrlich
- Antony van Leeuwenhoek
2. Who is the father of microbiology?
- Louis Pasteur
- Robert Koch
- Paul Ehrlich
- Joseph Lister
3. Who is the father of bacteriology?
- Louis Pasteur
- Robert Koch
- Paul Ehrlich
- Joseph Lister
4. Which bacteria is the human pathogen but still does not fulfil Koch's postulates criteria?
- Staphylococcus aureus
- Bacillus anthracis
- Mycobacterium leprae
- Psedomonas aeruginosa
5. Who is the father of chemotherapy?
- Louis Pasteur
- Robert Koch
- Paul Ehrlich
- Joseph Lister
6. Who is the father of immunology?
- Louis Pasteur
- Robert Koch
- Paul Ehrlich
- Edward Jenner
7. Which first human disease proved to be of viral origin?
- Smallpox
- Dengue
- Yellow fever
- Rabies
ANSWERS (MCQS)
Ans.
1. d; | 2. b; | 3. b; | 4. c; | 5. c; | 6. d; | 7. c |