Chapter 1: Humans & The Microbial World

Microorganism

a microscopic organism, especially a bacterium, virus, or fungus

Microbes

a microorganism, especially a bacterium, causing disease or fermentation

Biogenesis

Theory that life comes from previous life

Endospores

a heat-resistant asexual spore that develops inside some bacterial cells

Germ Theory of Disease

The principle that microorganisms cause diseases

Spontaneous Generation

The discredited belief that organisms can arise from non-living matter

Francesco Redi

Wanted to prove that worms found on rotten meat originated from fly eggs, not spontaneous generation.

Experiment: Put meat in a jar with one jar open, one jar sealed with gauze, and one jar sealed with a lid.

Conclusion: He disproved spontaneous generation, but it was not accepted till 200+ yrs.

John Needham

Experiment: Broths in a flask that was sealed to see if organisms would not grow if boiled (at that time, boiling was used to sterilize).

Conclusion: That boiling would sterilize all the microorganisms, proving spontaneous generation

Lazzaro Spallanzani

Experiment: Similar to Needham’s experiment, but differs by boiling the broth for a longer period of time, and he sealed the glass by melting the glass neck closed.

Conclusion: The flasks remained sterile free of microorganisms, but if the glass broke, then the microorganisms would enter. Leading to air affecting the growth of microorganisms.

Louis Pasteur

Experiment: Used swan-neck flasks and boiled the broth to demonstrate the effect air has on microorganisms, and filtered the air through a cotton plug.

Conclusion: If the flask was right side up, the air was able to escape, and there would be no microorganism growth, but when the flask was tilted so that air could reach the microorganisms, they grew.

John Tyndall

Proved that Pasteur’s theory was correct. That broth from some hay can contain living microorganisms after boiling, and these hay contained heat-resistant forms

Conclusion: Microorganisms exist in 2 forms

1. A cell is easily killed by boiling

2. A heat-resistant cell

Ferdinand Cohn

Discovered a heat-resistant form of bacteria called endospores