isolate the microorganism from diseased host in pure culture
infect a healthy animal with the microorganism and get the same disease
Isolate the same microorganism in pure culture from the infected host
Molecular Koch’s Postulates.
The phenotype or property under investigation should be associated with pathogenic members of a genus or pathogenic species.
Specific inactivation of the gene(s) associated with the suspected virulence trait should lead to a measurable loss in pathogenicity or virulence.
Reversion of the mutated gene should lead to restoration of pathogenicity: complementation.
Current molecular pathogenesis research is held to this standard. It is not always possible to satisfy the third rule for technical or physiological reasons.
Pathogens contain genes not found in their closely related counter parts
Genes specific to the pathogens are organized into islands, islet, atolls. That is, specific regions that are unique to the pathogens.
Pathogenicity islands encode those functions needed for the pathogen to causes a successful infection. It still needs the rest of the chromosome!
Pathogenicity islands have different G+C content than the backbone chromosome. Islands tend to be A+T rich, especially in Salmonella and E.coli.
PA’s can encode a specialized secretion apparatus designed to transfer effector proteins into the host. The proteins are specifically designed to alter host cell function. The proteins usually interact with a specific host protein or class of proteins.
Some but not all PA’s have inserted in a rare tRNA seltRNA. This insertion event does not interrupt the tRNA, but provides a powerful selection for the PA’s presence.
First isolated by Theobald Smith. S. Choleraesuis from porcine intestine around 1885. He worked for Daniel Salmon, who had nothing to do with the work.
1829- P.Ch.A. Louis in Paris separated typhoid from other fevers.
1884-Gaffkey Germany isolated Salmonella Typhi from spleens of infected patients
1896- first heat killed vaccine by Pfeiffer and Kalle.
