Koch’s Postulates and the Advent of Modern Medical Microbiology

Welcome to this week’s #micromeded. This week, we are talking about Koch’s Postulates and the recently developed #Molecular Koch’s Postulates. These postulates really served as the foundation for medical microbiology and offered a systematic approach to the study of microbes that cause disease. The main tenets of the original Koch’s Postulates include (1) recognizing the presence of an agent in all cases of disease, (2) isolating that org, (3) re-introducing the org causes similar symptoms, and (4) the org can be isolated again. Koch's postulates were limited, however. For instance, viral pathogens were not culturable in early microbiology labs, and symptomatic carriers break this protocol. Additionally, some pathogens do not exhibit the same presentation in mice.

With the advent of #metagenomics and complex molecular studies. The study of microbes has become incredibly complex, and we are starting to realize a disease state could be caused by a certain collection of microbes or a molecular marker present in many different species. The molecular postulates help bring the original set of guidelines into the genomic era. These postulates focus on molecular targets that cause disease (i.e.: genes encoding toxins, pili, receptors, etc.).

Determination of a pathogenic molecular target is determined by introducing that gene into a non-pathogenic strain of that species and observing the phenotype. Of course, the classical postulates could be utilized here, but the molecular postulates are more adaptable. For instance, the molecular postulates could be used in cases of a disease-causing gene in humans, bacteria, fungi, etc., but the approach could be done without having to inject a mouse to observe the clinical progression. Additionally, the molecular postulates could help us detect dysbiosis in the gut if certain genes (or certain taxa) are present in a metagenomic data set. The possibilities are endless…

Figure made using biorender.com