Microorganisms and Microbiology
Updated Fall 2015Jerald D. Hendrix
Historical Background
A. Discovery of microorganismsB. Spontaneous generation vs. BiogenesisC. Pure culture techniqueD. 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 microbesEarly 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 1800sJenner – small pox vaccineSnow – epidemic control via public health measuresSemmelweis – importance of hand-washingLister – antiseptic surgical methodsPasteur – rabies vaccineKoch – isolated anthrax and tuberculosis bacteria; Developed Koch’s postulates
D. Significance of Microbes
2. Microbes and the environment: late 1800sWinogradsky, Beijerinck, and others: established the role of microbes in biogeochemical cycling
3. Twentieth century microbiologyPublic health microbiologyDiscovery of virusesAntimicrobial chemotherapyMicrobial cell structure and biochemistryMicrobial genetics and genetic engineering