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