Bacteriophages in Bacterial Pathogenesis

Abstract Bacteriophages contribute to the virulence of many bacterial pathogens, largely by encoding the structural genes for virulence factors. The most widely recognized phage-encoded virulence factors are bacterial exotoxins, which account for the characteristic clinical manifestations of a number of human diseases caused by bacterial infections. The previous edition of this chapter focused primarily on phage-encoded toxins, but in the intervening years two themes have emerged (169). First, phages are increasingly recognized for encoding genes that contribute to other aspects of bacterial pathogenesis in addition to toxin production. In fact, phage-encoded gene products contribute to virtually every facet of bacterial pathogenicity, from attachment and invasion to immune evasion and transmission among humans. Second, while phages are like other mobile genetic elements in that they disseminate virulence genes among bacterial populations, phages have unique properties that enable them to contribute to bacterial pathogenesis by mechanisms other than transduction as well. For example, virion particles may themselves contain pathogenic components (12, 13); and prophage induction, through gene amplification, transcriptional upregulation, and phage-mediated lysis, can contribute to production and release of virulence factors from bacterial cells (167, 168). Owing to these developments, the contribution of bacteriophages to bacterial pathogenesis can no longer be conceived of simply as transduction of toxin genes that are regulated by the host bacterium. This chapter presents a summary of bacteriophage involvement in bacterial pathogenesis, in which we consider (i) the nature of the bacterial virulence properties altered by phages, (ii) the basic mechanisms by which phages alter these properties, and (iii) the regulation of the phage-related virulence property by the phage and/or its host bacterium.