Historical Background

1. Historical Background • Discovery of microorganisms • Spontaneous generation vs. Biogenesis • Pure culture technique • Significance of microbes

2. 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

3. 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

4. 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

5. 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

6. 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

7. 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

8. 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

9. Pure Culture Technique

10. Pure Culture Technique

11. Significance of Microbes • 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

12. Significance of Microbes • Microbes and the environment: late 1800s • Winogradsky, Beijerinck, and others: established the role of microbes in biogeochemical cycling • Twentieth century microbiology • Public health microbiology • Discovery of viruses • Antimicrobial chemotherapy • Microbial cell structure and biochemistry • Microbial genetics and genetic engineering