Microorganisms and Microbiology Updated Fall 2015 Jerald D. Hendrix

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

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