Safely teaching Koch's postulates on the causation of infectious disease

Abstract

Koch's postulates are a set of criteria by which the causation of infectious disease can be systematically tested. They also provide a basis for understanding virulence and host-parasite interactions in disease. The postulates can be applied more generally to interactions between microbe and host (or habitat) to identify and define the impact of the microbe in the system. Yoghurt, a fermented milk product generated by the synergistic action of two species of bacteria (Streptococcus thermophilus and Lactobacillus bulgaricus), can be used to demonstrate an interaction between ‘parasite’ (bacteria) and ‘host’ (milk) leading to the ‘symptoms’ of ‘lactic acidosis’ of the milk. This interaction can be safely examined in a minimally equipped laboratory, and provides practice in manipulative and analytical skills in basic microbiology, in the planning of controlled experiments, and in the testing of models to account for the changes wrought on milk by the ‘infecting’ bacteria. In terms of conceptual level and inf...