Textbook of Microbiology for GNM Students Ashutosh Debata, Darshan Panda, Sandeep Dhuper
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Introduction to MicrobiologyChapter 1

 
WHAT ARE MICROORGANISMS?
Microorganisms are microscopic organisms (very small and can only be seen by microscope). These may be unicellular (having a single cell) or multicellular (having more than one cell).
Table 1.1   General characteristics of microorganisms
Characteristics
Body plan
Single cell or cluster of cells
Organelles
They lack organelles
Size
Dimensions of microscopic organisms fall within the range of micrometers, sometimes nanometers
Most microbes extend from the smallest viruses to much bigger protozoans
Habitat
They are ubiquitous (found everywhere)
Classification
They are generally classified as : Archaea, Bacteria, Fungi, Viruses, Protozoa and Algae
Microorganisms to Environment
Microorganisms such as algae produce oxygen. They decompose organic material, provide nutrients for plants, etc.
Microorganisms to Humans
Some microorganisms are good for human health and some are pathogenic (causing severe diseases in human and animals)
Factors affecting Growth of Microorganisms
Nutrients, Oxygen, Water, Temperature, Acidity, Light and Chemicals affect the growth of microorganisms
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MICROBIOLOGY: STUDY OF MICROORGANISMS
Microbiology is the Scientific study of microorganisms. Various branches of Microbiology include:
  • Bacteriology: the study of bacteria.
  • Mycology: the study of fungi.
  • Protozoology: the study of protozoa.
  • Phycology (or algology): the study of algae.
  • Parasitology: the study of parasites.
  • Virology: the study of viruses.
  • Nematology: the study of the nematodes.
 
CATEGORIES OF MICROORGANISMS
Depending on their cell type, microorganisms are divided into (Flow chart 1.1);
 
Eukaryotic Microorganisms
They have complex cellular structure similar to those of human and animals. Their cells have nuclei and mitochondria. They are self-sufficient and capable of leading independent lives.
Examples
  • Fungi: Molds and yeasts
  • Helminthes: Tape worm, Hooke worms
  • Protozoa: Plasmodium
  • Unicellular Algae: Chlamydomonas
 
Prokaryotic Microorganisms
They are simple, self-sufficient, unicellular organisms having primitive nuclei and mitochondria being capable of leading independent lives.
Examples
  • Bacteria: E. coli, Vibrio cholerae
  • Archaebacteria: Thermobacillus SPS
  • Cyanobacteria: Spirulina SPS
 
Noncellular Microorganisms
They are without any cell forms and are called as acellular. They are of following types:
  • Viruses: They consist of DNA or RNA and proteins. They are not capable of leading independent lives. They grow and multiply by infecting cells of higher organisms (prokaryotic and eukaryotic cells).
  • Prions: They are made up of only proteins that cause Bovine Spongiform Encephalopathy (BSE), Kunue, etc.
  • Virusoids are madeup of single stranded RNA.
  • Viroidis are made-up of circular but single stranded RNA without protein. It causes Viral Hepatitis D
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Flowchart 1.1: Categories of microoganisms depending on their cell type
 
HISTORY OF MICROBIOLOGY
It was not very clear that microscopic living organisms exist. In 1600 AD Anton van Leeuwenhoek built his own microscopes and made first detailed descriptions of microscopic living creatures. Leeuwenhoek observed a variety of things like rain water, pond water and scrapings from his own teeth under the lens of his so-called microscope. He saw minute moving objects and called them as “Little animalcules”, such as protozoa, yeasts and bacteria. He made accurate sketches and communicated his findings to “Royal Society of London”. He had most likely observed single celled eukarytoic microbes. With this observation the Science of Microbiology was started. For this reason Anton van Leeuwenhoek is called as the Father of Microbiology.
 
CONTRIBUTION OF EMINENT SCIENTISTS TO MICROBIOLOGY EDWARD JENNER (1749–1823)
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Figure 1.1: Edward Jenner (1749–1823)
  • 4Jenner was an English doctor who discovered vaccination against small pox. This ultimately led to eradication of small pox.
  • He observed that dairy workers exposed to occupational (from their dairy job) cowpox infection were naturally immune to small pox.
  • In 1796, he experimentally proved that resistance to small pox can be induced by injecting cow pox material from disease pustules into man.
  • Jenner published his findings in 1798 in a pamplet “An inquiry into the cause and effect of variole vaccine”.
 
LOUIS PASTEUR (1822–1895)
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Figure 1.2: Louis Pasteur (1822–1895)
Era
Discoverer
Important Events
Eighteenth
Century
Edward Jenner (1729–1799)
Discovery of small pox vaccine
Nineteeth
Century
Justus von Liebig
(1803–1873)
Conceptualized the physico-chemical theory of fementation
Ignaz Phillipp Semmelwets (1818–1865)
First and foremost introduced the application of antiseptics.
Joseph Lister (1827–1912)
Developed aseptic techniques: Isolated bacteria in pure culture.
Fenny Hesse (1850–1934)
Suggested use of agar as a solidifying material for the preparation of microbiological media.
Paul Ehrlich (1854–1915)
Developed modern concept of chemotherapy and chemotherapeutic agents.
Hans Christian Gram
(1853–1933)
Invented vital and important procedure for differential staining of microorganisms, i.e. the well-known Gram Stain.
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Twentieth
Century
August von Wassermann (1866–1925)
Developed complement-fixation test for syphillis.
Martinus Williem Beijerinek (1851–1931)
Employed the principles of enrichment cultures: confirmed finding of the very first virus.
Felix H.d' Herelle
(1873–1949)
Discovered independently the bacteriophages, i.e. viruses that destroy bacteria.
  • He was a Professor of Chemistry at the University of Lille, France.
  • He is also called as “Father of Modern Microbiology”.
  • Generation”(Abiogenesis), experimentally by using swan-necked flasks experiment.
  • He experimentally showed that souring of wine and beer is due to the growth of undesirable organisms.
  • He also showed that the desirable microorganisms produce alcohol by a chemical process called “Fermentation”.
  • He introduced the technique of “Pasteurization” and proposed the “Germ theory of disease”.
  • 6He developed steam sterilization technique, today popularly called as autoclaving.
  • He experimentally differentiated between aerobic and anaerobic bacteria and coined the term “anaerobic” to refer the organisms that do not require oxygen for growth.
  • He developed anthrax vaccine.
  • He also developed a vaccine against rabies (Hydrophobia).
 
ROBERT KOCH (1843–1912)
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Figure 1.3: Robert Koch (1843–1912)
  • He was a German doctor who later became the Professor of hygiene and Director of Institute of Infective Diseases at Berlin.
  • He is known as Father of practical bacteriology.
  • He is also regarded as “Father of Medical Microbiology and Bacteriology”.
  • He discovered Bacillus anthracis, the causal organism of the disease Anthrax.
  • He introduced staining techniques for the study of disease causing microorganisms.
  • He discovered Mycobacterium tuberculosis which causes Tuberculosis in human beings.
  • He also discovered Vibrio cholerae, the causative agent of Cholera disease.
  • 7He developed pure culture techniques by introducing solid media.
  • He had a great contribution in the development of pure culture techniques.
  • He gave Koch's Postulates.
 
JOSEPH LISTER (1827–1912)
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Figure 1.4: Joseph Lister (1827–1912)
  • He was a Professor of Surgery at University of Glassglow and Edinburg and later at King's College, London.
  • He is also known as “Father of Antiseptic Surgery”.
  • He was the first person to use an antiseptic solution during the process of surgery.
  • He used Carbolic Acid (phenol) on the wound during surgery which successfully prevented sepsis (infection) after operation.
  • He also introduced application of carbolic acid during wound dressing.
  • Lister's antiseptic surgery later led to the development of aseptic surgery.
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ELIE METCHNIKOFF (1845–1916)
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Figure 1.5: Elie Metchnikoff (1845–1916)
  • Elie Metchnikoff, a Russian-French Biologist, discovered the phenomenon of phagocytosis.
  • He discovered the process of phagocytosis in the transparent larvae of starfish.
  • The cells which carry out phagocytosis are called as phagocytes.
  • While working at Pasteur Institute in Paris, he found that in human blood leukocytes carry out phagocytosis against invading bacteria.
  • Large number of leukocytes gather in the infected area which results in swelling, reddening and pain due to dead phagocytes forming pus.
 
ALEXANDER FLEMING (1881–1955)
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Figure 1.6: Alexander Fleming (1881–1955)
  • 9He was an English Scientist who worked at ST. Marry's hospital in London.
  • He discovered lysozyme in 1922 by demonstrating that nasal secretion (fluid from nose) has the power of killing certain bacteria.
  • Lysozymes are enzymes present in body fluids such as tears, sweat, and nasal fluid that have the power to kill certain bacteria.
  • In 1929, he made an accidental discovery of the antibiotic Penicillin from the fungus Penicillium notatum.
  • In 1945 Fleming, Florey and Chain shared the noble prize in physiology and medicine for the discovery of Penicillin.
 
PAUL EHRLICH (1854–1915)
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Figure 1.7: Paul Ehrlich (1854–1915)
  • He was a German Bacteriologist who invented the technique of Chemotherapy in medicine.
  • He is also called as “Father of Chemotherapy”.
  • The very concept of Chemotherapy is based on the fact that organisms causing diseases could selectively be killed with chemical drugs without harming the host.
  • He produced the first synthetic drug – Arsphenamine to control the Syphilis disease.
  • He also observed that drug would undergo certain changes in the body after it would produce desired action.
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POSSIBLE QUESTIONS
  1. What is microbiology? Write an essay on the history of microbiology.
  2. What are microorganisms? Give an account of their characteristic features.
  3. Write Short Notes
    • Louis Pasteur
    • Germ theory of disease
    • Pasteurization
    • Robert Koch
    • Koch's postulates
    • Edward Jenner
    • Joseph Lister
    • Antiseptic Surgery
    • Penicillin
    • Lysozyme
    • Paul Ehrlich