The molecular postulates can be briefly summarized as follows:
- The virulence trait under study should be associated much more with pathogenic strains of the species than with nonpathogenic strains.
- Inactivation of the gene or genes associated with the suspected virulence trait should substantially decrease pathogenicity.
- Replacement of the mutated gene with the normal wild-type gene should fully restore pathogenicity.
- The gene should be expressed at some point during the infection and disease process.
- Antibodies or immune system cells directed against the gene products should protect the host.