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Chapter 2 : Antigenic Variation and the Persistence of Extracellular Bacteria in Vertebrate Hosts
Category: Bacterial Pathogenesis
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This chapter examines the persistent bacterial pathogens within the context of evolutionary ecology by addressing the functional and evolutionary aspects of the mechanisms that bacteria have developed to persist in mammalian hosts. The focus will be on antigenic variation, as this is one of the most widely studied aspects of persistence and also one of the most variable in terms of the extent to which extracellular pathogens have developed genetic mechanisms to enable variation to occur. A recent paper has provided an overview of the significance of antigenic variation in terms of the evolutionary forces driving host-pathogen coevolution. A distinction among conjugation, transduction, and transformation is that the first two processes are largely driven by factors external to the cell receiving the DNA while transformation is largely under the control of the recipient cell. Pathogenicity islands, consisting of large blocks of DNA encoding multiple, and frequently related, gene products, have been identified in some bacterial populations. The emergence of intracellular antigenic variation may be a multifactorial process, governed by the population biology of the organism, the response of the vertebrate host, and the specific bacterial interactions encountered within the host environment. Analysis of the mechanisms and population biologies of bacterial persistence within and between hosts is only one area in which a greater understanding of microbial evolution will facilitate proactive approaches for the control of infectious disease.