Chapter prelims

• Microorganisms are considered to be transitional forms of either plants or animal kingdom
• Kingdom Protista includes unicellular microorganisms such as viruses, bacteria, fungi, protists, and algae
• There are two classes of protists:

  • Higher protists (Eukaryotes) include algae, protozoa, fungi, and molds
  • Lower protists (Prokaryotes) include bacteria and viruses
• Microbiology is the study of very small living organisms that can only be viewed under a microscope
• Binary fission is the reproduction of a cell by division into two approximately equal parts, which is the mode of reproduction for bacteria
• Bacteria are unicellular microorganisms with shapes such as spherical, round, and spiral forms, and they move using flagella
• Fungi are heterotrophic microorganisms that need organic compounds for metabolic synthesis, have a cell wall made of chitin, and are classified in a kingdom called thallophyta
• Protozoa are eukaryotic microorganisms, such as Amoeba and algae, abundant in ponds and fresh water
• Viruses are the smallest of cell microorganisms, ultramicroscopic and intracellular parasites, with DNA or RNA genomes, surrounded by a capsid (protein shell) and an additional outer membrane called an envelope
• Bacteriophages are viruses that infect and parasitize bacteria
• Brief history of microbiology:

  • Robert Hooke discovered the cell theory in 1665
  • Anton van Leeuwenhoek was the first to view living cells in 1673
  • Debate over spontaneous generation involved scientists like Francesco Redi, John Needham, Lazzaro Spallanzani, Rudolph Virchow, and Louis Pasteur
  • Louis Pasteur resolved the issue of spontaneous generation and introduced aseptic techniques
  • The Golden Age of Microbiology (1857-1914) saw contributions such as pasteurization, fermentation, and the germ theory of disease
• Modern developments in microbiology include virology, immunology, and recombinant DNA technology
• Recombinant DNA technology involves molecular biology and microbial genetics, with key figures like James Watson, Francis Crick, Francois Jacob, Jacques Monod, and Paul Berg
• Branches of microbiology include general microbiology, medical microbiology, public health microbiology, agricultural microbiology, microbial microbiology, food and dairy microbiology, industrial microbiology, veterinary microbiology, microbial genetics and molecular biology
• Naming and classifying microorganisms:

  • Scientific names are traditionally used in Latin language
  • Ernst Heinrich Haeckel proposed the classification system with three kingdoms: Plantae, Animalia, and Protista
  • Robert Whittaker classified microorganisms based on cellular and organizational patterns, including Plantae, Animalia, Fungi, Protist, and Monera (prokaryotes)
  • Carl Woese proposed the three primary super kingdoms: Bacteria (Eubacteria), Archaea, and Eukarya
• Average size of bacteria

  0.2 to 5.0 microns
• Prokaryotic cells lack membrane-bound nucleus or other membrane-enclosed structures.
• Microscopic organism that can be seen only under high magnification is called a bacterium.
• Bacteria have a single circular chromosome that is not enclosed by a nuclear envelope.
• Cell walls may be present, composed of peptidoglycan in gram-positive bacteria and lipopolysaccharide in gram-negative bacteria.
• Gram staining is a method used to differentiate between two types of bacteria based on their ability to retain crystal violet dye.
• Fungi:

  • Heterotrophic microorganism that requires organic compounds (nitrogen and carbon) for metabolic synthesis
  • Multicellular protein lacking differentiation of roots, stem, leaves
  • Classified in the kingdom Thallophyta, a group of plants or plant-like organisms without stems, roots, or leaves
  • Cell wall made of chitin
• Protozoa:

  • Eukaryotic microorganism found in ponds and freshwater
  • Examples include Amoeba and algae (photosynthetic eukaryotes with cell walls made of cellulose)
• Virus:

  • Smallest cell microorganism with an average size of 0.01-0.3 microns
  • Ultramicroscopic and intracellular parasites
  • Contains DNA or RNA as its genome
  • Surrounded by a capsid (protein shell) and an additional outer membrane called an envelope
• Bacteriophage:

  • Viruses that infect and parasitize bacteria
• Anton van Leeuwenhoek (1673):

  • Dutch merchant and microscope maker
  • First to view living cells (organisms)
  • Used a simple, handheld microscope to view pond water and scrapings from his teeth
  • Amateur scientist
  • Probably the first to observe microorganisms through magnifying lenses
  • Wrote a series of letters to the Royal Society of London from 1674-1723, describing the animalcules
  • Referred to microorganisms as "animalcules"
• Robert Hooke (1665):

  • Discovered the cell theory
  • Reported that the smallest life units are cells, which he described as "little boxes"
  • Was able to see individual cells with the compound microscope he developed
  • His discovery marked the beginning of the cell theory
  • Only saw cells and not microorganisms because he did not use staining techniques
• Francesco Redi (1668):

  • Italian physician
  • Demonstrated that maggots arise spontaneously from decaying meat
  • Maggots can only arise if it enters the jar
  • He had 3 jars containing meat
• John Needham (1745):

  • English man
  • Claimed that microorganisms could arise spontaneously from heated nutrient broth (pork and chicken broth)
  • Found out that even after heating the nutrient broth, the cover does not have any microorganisms or bacteria
  • If the broth is open after heating, there are still microorganisms that can be alive
• Lazzaro Spallanzani (1765):

  • Italian scientist
  • Suggested that microorganisms had probably entered the solution because of the air
  • Repeated the experiment and claimed that the microorganisms came from the air
  • Unresolved issue
• Rudolph Virchow (1858):

  • Challenged the notion with his theory of biogenesis (living cells arise from pre-existing cells)
• Louis Pasteur (1861):

  • French scientist
  • Resolved the issue about spontaneous generation
  • Boiled the broth and the flask at the same time
  • His discovery led to Aseptic technique to prevent contamination of microorganisms present in the air
• Golden Age of Microbiology (1857-1914):

  • Contributions of the scientists:
  • Pasteurization
  • Fermentation
  • Germ theory of disease
• Germ Theory of Disease:

  • Includes Louis Pasteur (1865)
  • Found out how to kill silkworm
  • Sought help from Agustino Bassi (1835) who proved that silkworm disease can be caused by fungus
• Joseph Lister (1860):

  • English surgeon
  • Applied the germ theory to medical procedures
  • Made a soak dressing with carbolic acid to kill microorganisms and bacteria
• Ignaz Semmelweis (1840):

  • Demonstrated how a physician going to a diseased patient without disinfecting hands can cause or transmit disease
  • Childbirth fever or Puerperal fever
• Robert Koch (1876):

  • Brilliant German physician
  • First professor to prove that microorganisms can transmit disease through scientific steps
  • Discovered the rod-shaped "Ranchi bacillus" aka "Bacillus anthracis" causing anthrax
  • Used Koch's postulate to prove that a particular microorganism can cause a particular disease
• Modern Development in Microbiology:

  • Contributions:
  • Virology - study of viruses
  • Immunology - study of immunity
  • Recombinant DNA technology
• In Virology:

  • Dmitri Ivanovsky (1892):
  • Discovered the Tobacco Mosaic Virus (TMV), the first viral pathogen
  • Wendell Stanley (1935):
  • Discovered viruses made with nucleic acid and proteins
• Digestion is the process of breaking down food into smaller molecules that can be absorbed by the body