Quick questions on Koch and Pasteur, and Koch's postulates: HSC Biology Module 7

Swan-neck flask experiment (1859). Pasteur boiled nutrient broth in glass flasks with long, curved necks. The broth remained sterile indefinitely because airborne microbes settled in the curve of the neck before reaching the liquid. When he broke the necks or tilted the flasks so that broth contacted the trapped microbes, the broth quickly grew cloudy with microbial growth.

Anthrax (1876). Koch isolated Bacillus anthracis from infected sheep, cultured it on the cut surface of a potato, injected the pure culture into healthy mice, observed identical disease, and re-isolated the same bacterium. This was the first time a specific microbe was definitively linked to a specific disease.

Koch's four criteria for proving that a specific microbe causes a specific disease:

Asymptomatic carriers. Some pathogens (Salmonella Typhi, Mycobacterium tuberculosis) are present in healthy carriers, breaking postulate 1.

Pasteur boiled nutrient broth in glass flasks with long, curved necks. The broth remained sterile indefinitely because airborne microbes settled in the curve of the neck before reaching the liquid. When he broke the necks or tilted the flasks so that broth contacted the trapped microbes, the broth quickly grew cloudy with microbial growth.

Life does not arise spontaneously. Microorganisms in broth come from other microorganisms in the air. This disproved spontaneous generation and supported germ theory.

Pasteur developed attenuated (weakened) vaccines for chicken cholera (1879), anthrax (1881) and rabies (1885), founding modern immunisation.

He showed that gentle heating of wine, beer and milk killed spoilage microbes without destroying the product. Pasteurisation of milk dramatically reduced food-borne tuberculosis.

Koch isolated Bacillus anthracis from infected sheep, cultured it on the cut surface of a potato, injected the pure culture into healthy mice, observed identical disease, and re-isolated the same bacterium. This was the first time a specific microbe was definitively linked to a specific disease.

Koch identified Mycobacterium tuberculosis and Vibrio cholerae, developing acid-fast staining to visualise the slow-growing tuberculosis bacterium.

Koch's lab developed solid agar plating (suggested by Fanny Hesse), pure culture isolation, and improved staining methods. These techniques remain standard in microbiology laboratories.

Some pathogens (Salmonella Typhi, Mycobacterium tuberculosis) are present in healthy carriers, breaking postulate 1.

Viruses cannot be grown without host cells, and many bacteria (e.g. Treponema pallidum, the syphilis pathogen) are difficult to culture. This breaks postulate 2.

Postulate 3 requires deliberately infecting a healthy host, which is not ethical in humans. Animal models, organoids and molecular Koch's postulates (linking specific genes to disease) now supplement the originals.

Some diseases require co-infection or specific host susceptibilities.