Bacteriophages and virulence evolution

Abstract

A major virulence factor for Salmonella spp., as well as for a variety of other animal and plant bacterial pathogens, is the type III secretion system (TTSS). The TTSS allows the transfer of bacterial effector proteins into eukaryotic cells and can thus modulate host-cell signal transduction. The majority of Salmonella typhimurium TTSS effector proteins are encoded by genes located on pathogenicity island 1 (SPI-1). Now, Mirold et al.1xIsolation of a temperate bacteriophage encoding the type III effector protein SopE from an epidemic Salmonella typhimurium strain. Mirold, S. et al. Proc. Natl. Acad. Sci. U. S. A. 1999; 96: 9845–9850Crossref | PubMed | Scopus (161)See all References1 have reported that the sopE gene, encoding one of the effectors of the SPI-1 TTSS, is located outside this pathogenicity island on the temperate bacteriophage SopEΦ. sopE is present only in a small number of S. typhimurium isolates, but these isolates all carry SopEΦ sequences. By lysogenic conversion, SopEΦ can horizontally transfer genes between different S. typhimurium strains and could, therefore, cause the emergence of new epidemic strains. Indeed, most of the isolates harboring SopEΦ belong to the small group of epidemic strains of S. typhimurium that have been responsible for a large proportion of human and animal salmonellosis and have persisted for a long period of time. These data suggest that bacteriophages might provide an efficient mechanism for fine-tuning or acquiring new methods of interaction between bacterial pathogens and their hosts.