Overview
This lecture introduces the history, key discoveries, and foundational concepts of microbiology, focusing on microorganisms, their classification, and their role in disease and the environment.
Origins and Early Discoveries in Microbiology
- Robert Hooke first observed microorganisms (bread mold) in 1665 with a microscope.
- Antony van Leeuwenhoek observed bacteria and called them "animalcules," recognizing them as independent living cells.
Spontaneous Generation vs. Biogenesis
- Spontaneous generation: the (incorrect) belief that life arises from non-living matter.
- Biogenesis: the correct idea that life comes from pre-existing living organisms.
- Louis Pasteur disproved spontaneous generation using the swan-neck flask experiment, showing sterilized broth remained sterile unless exposed to microbes.
- John Tyndall discovered endospores, dormant bacterial forms not killed by boiling, explaining some experimental contamination.
Microorganisms and Disease
- Infection: growth of a microbe within another organism, not always causing disease.
- Disease: tissue damage or functional alteration; can occur with or without infection.
- Koch’s postulates outline steps to prove a microbe causes a disease: presence in all cases, isolation, causation in a healthy host, and re-isolation.
Limitations of Koch's Postulates
- It is unethical to intentionally experiment with disease-causing microbes in humans; animal models are used instead.
Types and Importance of Microbes
- Microbes: organisms too small to be seen without a microscope.
- Living microorganisms include bacteria, protozoa, algae, fungi, and some parasites (all cellular).
- Non-living microbes include viruses, viroids, and prions (non-cellular).
Role of Microorganisms in the Environment
- Microorganisms enable nitrogen fixation, oxygen production, and cellulose breakdown.
- Used in food/beverage production (e.g., fermentation) and bioremediation of pollutants.
- Serve as biological research models due to rapid growth and low maintenance cost.
Cell Types and Domains
- Two cell types: prokaryotes (no nucleus; bacteria and archaea) and eukaryotes (true nucleus; algae, fungi, protozoa).
- Three life domains: Bacteria, Archaea (both prokaryotic), and Eukarya (eukaryotic).
- Bacteria have peptidoglycan cell walls; archaea live in extreme environments and lack peptidoglycan.
Microbial Nomenclature
- Uses binomial system: Genus (capitalized, italicized) + species (lowercase, italicized).
- Genus indicates relatedness among species.
Key Terms & Definitions
- Microbe — Any organism too small to be seen with the naked eye.
- Microorganism — Living microbe (cellular); includes bacteria, protozoa, etc.
- Endospore — Dormant, heat-resistant bacterial form.
- Infection — Microbial growth within another organism.
- Disease — Tissue damage or lost function, often with symptoms.
- Prokaryote — Cell without a nucleus (bacteria, archaea).
- Eukaryote — Cell with a true nucleus and organelles.
- Domain — Highest taxonomic classification (Bacteria, Archaea, Eukarya).
- Peptidoglycan — Protein-carbohydrate compound in bacterial cell walls.
Action Items / Next Steps
- Review and study the PowerPoint slides for exam preparation.
- Understand and memorize key definitions and differences between prokaryotes and eukaryotes.
- Prepare for questions regarding historical experiments and Koch’s postulates.