Covert Operations: the Adaptable Plan of Attack Deployed by Pathogenic Bacteria

Bacterial pathogenesis may be viewed as a developmental program wherein the virulence traits observed are the summation of the relative contributions of nature versus nurture; i.e., a series of complex interactions between bacterial genes and the environments experienced during the infective process. Repression or inhibition of virulence functions may also improve bacterial fitness by mediating immune avoidance mechanisms, the establishment and maintenance of subclinical infections, or bacterial transmission to new hosts or the environment. Owing to the dehydration associated with massive diarrhea (several liters/day), cholera is one of the most rapidly fatal diseases known. Analysis of the coordinate control of bacterial virulence gene expression in response to environmental and genetic signals in the laboratory setting (in vitro) has contributed significantly to defining the functions that confer microbial pathogenicity. This chapter talks about Vibrio cholerae, Shigella spp, and Salmonella spp in detail. The study of microbial pathogens in the context of their natural host(s) provides insights into microbial pathogenicity that cannot be revealed from in vitro studies alone. Classification of virulence genes based on their preferential expression in host tissues provides a means to understand the ecology of infection as well as spatial and functional relationships between bacterial and host gene products. The currently available means to determine the level of expression of all messenger RNA (with DNA arrays) and all proteins (with two-dimensional analyses) will permit the determination of gene activation and protein expression during the varied stages of infection.