Experimental Approaches to Understanding Pathogenesis

Understanding bacterial pathogenesis starts with considering the notion of disease. Many different and complementary approaches can be used to identify bacterial genes that are important for infection. Regardless of the initial method for identification, fulfilling “molecular Koch's postulates” has become the gold standard for the confirmation of virulence factor genes. Following initial identification, using one or more of the comparison-, observation-, or disruption-based techniques, the gold-standard method for confirming the activity of a novel virulence factor is to construct a clean deletion mutant of the gene and examine the effect of this mutation on pathogenesis. The methods available to study bacterial pathogenesis differ depending on the bacterium and the host. This chapter presents the contrasting stories of how two virulence factors were identified and characterized in two different bacterial pathogens ( Pasteurella multocida , Mycoplasma bovis ). P. multocida is a Gram-negative bacterium that causes a variety of diseases in livestock animals.