History of Microbiology Nature of Science Early Observations Spontaneous Generation Controversy Germ Theory of Disease

Nature of Science Science is systematized knowledge developed through the application of the scientific method Scientific method Observations (objective vs. subjective) Formulate hypothesis Test hypothesis with controlled experiments Accept, revise or reject hypothesis

Early Observations & Experiments Microscopes van Leeuwenhoek & Hooke Spontaneous Generation Controversy Germ Theory of Disease & Robert Koch

Spontaneous Generation Biogenesis vs. Abiogenesis Aristotle Jan Baptista van Helmont (1580-1644) Francisco Redi (1626-1697) John T. Needham (1713-1781) Lazzaro Spallanzani (1729-1799) Theodor Schwann (1810-1882) Louis Pasteur (1822-1895)

Biogenesis vs. Abiogenesis Biogenesis - development of life from preceding life forms Abiogenesis - life arises from inorganic or non-living materials

Aristotle first to record possible routes to life. He saw beings as arising in one of three ways, from sexual reproduction, asexual reproduction or nonliving matter. observable that aphids arise from the dew on plants, fleas from putrid matter, and mice from dirty hay this belief remained unchallenged for more than two thousand years.

Jan Baptista van Helmont (1580-1644) Reported in late 1500’s that barley grains and old shirts left in a corner would spontaneously give rise to mice Claimed as evidence that supported spontaneous generation or abiogenesis

Francisco Redi (1626-1697) Set up controlled experiment to test idea of spontaneous generation with respect to maggots appearing on rotting meat open jar with meat screened jar with meat sealed jar with meat

von Helmut open screened sealed

John T. Needham (1713-1781) Flies do not arise spontaneously but the “animalcules” described by van Leeuwenhoek must In 1748 Needham boiled mutton broth, stoppered and noted that flask becam turbid Argued that the turbidity, which included many “animalcules” must have arisen spontaneously

Lazzaro Spallanzani (1729-1799) Repeated Needham’s experiments Used flasks that were sealed by melting the glass rather than with a cork Found that if sealed properly, flasks boiled 45 minutes would remain sterile thus refuting Needham’s conclusions

Theodor Schwann (1810-1882) An argument against Spallanzani experiments is that they excluded air Constructed apparatus to sterilize air coming into flask Results supported biogenesis

Theodor Schwann (1810-1882) Apparatus used by Schwann The central flask, which is being rendered sterile by heating contains the infusion. Air is passed through it from the heated coil on right. The flask at left is a mercury trap through which air escapes after passing through the central flask.

Louis Pasteur (1822-1895) Looked at air which had been filtered Developed swan neck flask to deal with heated air problem Looked at frequency of occurrence of contaminated flasks Settled controversy

Louis Pasteur (1822-1895) An example of the swan-necked flask

Germ Theory of Disease Observation on causative agents of potato blight and diseases of silkworms led to hypothesis Formalized through work of Pasteur and Koch (and others) led to theory that germs or microorganisms may cause disease

Germ Theory of Disease Robert Koch first developed relationship between microorganisms and disease Developed Koch’s Postulates for testing relationship Discovered cause of anthrax and tuberculosis

Germ Theory of Disease Koch’s Postulates: Same microorganism must be observed in every instance of disease Organism must be isolated from diseased host and grown in pure culture Specific disease must be reproduced when pure culture is reintroduced into host