from Raphael H. Valdivia writing in Bacterial Pathogenesis: Molecular and Cellular Mechanisms:
The identification of factors that enhance the virulence of bacteria is a critical step in understanding the molecular basis for their pathogenesis. Over the last several years, molecular and genetic strategies have been developed to identify bacterial virulence determinants. These approaches, combined with rapidly advancing genome technologies, have allowed investigators to map the pathogen's transcriptional responses to the host environment and to define the relative contribution of individual genes to the infectious process. This chapter highlights some of the many approaches currently under use. Genes that enhance the ability of bacteria to infect, to evade host immune responses, and to disseminate are commonly referred to as virulence genes. These genes may encode factors ranging from toxins and adhesins, with readily recognized roles in disease causation, to enzymes that enhance the pathogen's metabolic properties within the host's nutrient-limiting environment. Identifying virulence genes and determining the function of their encoded products is central to our understanding of microbial pathogenesis.
Further reading: Bacterial Pathogenesis: Molecular and Cellular Mechanisms