Microbiology and Disease Theories

Overview

This lecture covers the development of cell theory, germ theory of disease, key experiments in microbiology, and the shift toward controlled biological processes like bioengineering.

Cell Theory and the Study of Microbes

• Microbes are single-celled organisms responsible for processes like fermentation and disease.
• Schleiden and Schwann proposed around 1837 that all living things are made of cells, the fundamental unit of life.
• Both scientists noticed nuclei inside cells, hinting at their importance for life.
• Thomas Henry Huxley described cells as factories with different parts serving specific functions.

Disease Theories: Miasma vs. Germ Theory

• In the early 1800s, diseases were thought to be caused by miasma, or foul-smelling air from decay.
• Miasma theory seemed reasonable because microbes do grow on decaying, smelly matter.
• Germ theory, pushed by scientific rebels, argued that specific microorganisms cause infectious diseases.

John Snow and Cholera

• John Snow mapped a cholera outbreak in London in 1854 and linked cases to a contaminated water well.
• Removing the well handle reduced cholera cases, suggesting waterborne microbes caused the disease.
• Snow’s investigation supported, but did not prove, germ theory.

Louis Pasteur and Microbiology

• Louis Pasteur, a French chemist, linked yeast to fermentation and proved microbes cause wine to ferment.
• Pasteur developed pasteurization (heating liquids to kill microbes) in 1865 to prevent spoilage.
• He was instrumental in disproving spontaneous generation, showing life comes from life (biogenesis).
• Pasteur advanced immunology by developing weakened vaccines, starting with chicken cholera in 1879.

Robert Koch and Bacteriology

• Robert Koch established that specific microbes cause specific diseases like anthrax and tuberculosis.
• Koch’s four postulates outlined criteria for linking a microbe to a disease.
• He and his team identified microbes responsible for many major diseases.

Early Bioengineering: Jacques Loeb

• Jacques Loeb induced artificial parthenogenesis (virgin birth) in sea urchins by changing salt solutions.
• Loeb’s work marked early bioengineering, treating cells as machine parts to be manipulated by humans.

Key Terms & Definitions

• Microbe — a microscopic, usually single-celled organism.
• Cell theory — all living things are made of one or more cells.
• Miasma theory — belief that diseases are caused by "bad air" from decaying matter.
• Germ theory — specific microbes (germs) cause specific diseases.
• Fermentation — microbial transformation of sugars into alcohol and carbon dioxide.
• Pasteurization — heating liquids to destroy microbes.
• Biogenesis — the principle that living things come only from other living things.
• Vaccine — a substance used to stimulate immunity against a disease.
• Koch's postulates — four criteria to establish a causal relationship between a microbe and a disease.
• Bioengineering — manipulation of living cells or organisms for practical purposes.

Action Items / Next Steps

• Review definitions and significance of cell theory, germ theory, and Koch’s postulates.
• Prepare for next lecture on Mendel and genetic variation.