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					        I.     Historical
               Background
A.   Discovery of microorganisms
B.   Spontaneous generation vs. Biogenesis
C.   Pure culture technique
D.   Significance of microbes
    A. Discovery of Microbes

Anton van Leeuwanhoek
– Mid-1600s
– Developed early microscope
– First to observe microbes: “animicules”
– Did not appreciate the significance or
  impact of microbes on human life
       B. Spontaneous
          Generation vs
          Biogenesis
Aristotle
– Suggested that mice could develop by spontaneous
  generation
Redi
– Mid-1600s
– Experimentally demonstrated that maggots (fly
  larvae) do not develop via spontaneous generation
    B. Spontaneous
       Generation vs
       Biogenesis
Needham vs Spallanzani
– Mid-1700s
– Spallanzani demonstrated that microbes do not
  develop by spontaneous generation in sterile nutrient
  media sealed in flasks
– Needham criticized Spallanzani’s work: asserted that
  spontaneous generation required fresh air in the
  flask
    B. Spontaneous
       Generation vs
       Biogenesis
Pasteur
– Mid to late-1800s
– French chemist and a “founder” of the modern
  science of microbiology
– Settled the Spallanzani-Needham debate with the
  “swan-necked flask” experiment
– Worked on many important problems in
  microbiology, most notably in vaccine production
– Aseptic technique
    B. Spontaneous
       Generation vs
       Biogenesis
Tyndall
– Late 1800s
– Demonstrated directly that the growth of microbes in
  contaminated flasks was due to microbial cells from
  airborne dust particles, not from spontaneous
  generation
– Developed a method (tyndallization) to ensure
  sterilization of media through repeated boiling
       C. Pure Culture
          Technique
Pure culture
– A sample of microbial growth that contains only a
  single species
– Challenging to obtain because of the large numbers
  and small sizes of microbes
Early attempts
– “Limiting dilution” method in broth medium used by
  Pasteur and others
– Difficult to ensure that a single species exists in the
  culture
      C. Pure Culture
         Technique
Streak plate method
– Developed in the 1870s by Koch and his co-workers
– The objective: to obtain isolated colonies – spots of
  microbial growth that come from a single parent cell
– The method: streak the sample on semisolid
  medium, containing a gelling agent
– Agar: the most commonly used gelling agent
C. Pure Culture
   Technique
C. Pure Culture
   Technique
      D. Significance of
         Microbes
1. Microbes and disease: late 1700s – late 1800s
      Jenner – small pox vaccine
      Snow – epidemic control via public health
      measures
      Semmelweis – importance of hand-washing
      Lister – antiseptic surgical methods
      Pasteur – rabies vaccine
      Koch – isolated anthrax and tuberculosis bacteria;
      Developed Koch’s postulates
      D. Significance of
         Microbes
2. Microbes and the environment: late 1800s
      Winogradsky, Beijerinck, and others: established
      the role of microbes in biogeochemical cycling
3. Twentieth century microbiology
      Public health microbiology
      Discovery of viruses
      Antimicrobial chemotherapy
      Microbial cell structure and biochemistry
      Microbial genetics and genetic engineering