Editing Koch's postulates (section)

== Molecular Koch's postulates ==
In 1988, microbiologist [[Stanley Falkow]] developed a set of three [[Molecular Koch's postulates]] for identifying the microbial genes encoding [[virulence factor]]s. First, the [[phenotype]] of a disease symptom must be associated with a specific [[genotype]] only found in pathogenic strains. Second, that symptom should not be present when the associated gene is inactivated. Third, the symptom should return when the gene is reactivated.<ref name="falkow88">{{cite journal | vauthors = Falkow S | title = Molecular Koch's postulates applied to microbial pathogenicity | journal = Reviews of Infectious Diseases | volume = 10 | issue = Suppl 2 | pages = S274–S276 | year = 1988 | pmid = 3055197 | doi = 10.1093/cid/10.Supplement_2.S274 }}</ref>

Modern [[DNA sequencing]] allows researchers to identify whether the genes of specific pathogens are only present in infected hosts, offering a modified approach for determining correlation between viruses and certain diseases. Since viruses cannot grow in [[axenic]] cultures, requiring a host cell to hijack for growth and replication, scientists are limited to analyzing which viral genes contribute to host diseases. Additionally, this method has supported correlations between [[prion]]s (pathogenic misfolded proteins) and conditions like [[Creutzfeldt–Jakob disease]] because Koch's postulates are focused on foreign microorganisms, rather than the results of host mutations.<ref name="fredricks96">{{cite journal | vauthors = Fredricks DN, Relman DA | title = Sequence-based identification of microbial pathogens: a reconsideration of Koch's postulates | journal = Clinical Microbiology Reviews | volume = 9 | issue = 1 | pages = 18–33 | date = January 1996 | pmid = 8665474 | pmc = 172879 | doi = 10.1128/CMR.9.1.18 }}</ref>