Contribution of Phages to Group AStreptococcusGenetic Diversity and Pathogenesis

Abstract

The majority of research conducted in the field of streptococcal phages has concentrated on group A Streptococcus (GAS) phages. Therefore, the majority of this chapter reviews GAS phages. However, when pertinent, the chapter also discusses phages from group C Streptococcus (GCS) and group G Streptococcus (GGS). The results of comparative genomics described in this chapter have led to two predictions regarding the acquisition of phage-encoded virulence factors and GAS pathogenesis. First, it is the particular array of phage-encoded virulence factors, rather than simply the presence or absence of a single phage-encoded virulence factor, that significantly affects GAS pathogenesis by promoting the colonization of new hosts or the occupation of new biologic niches. Second, the complex pathogenesis of GAS is related to polylysogeny. Importantly, the genome sequences identified previously unknown phages and phage-encoded virulence factors, thereby raising the possibility that sequencing the genomes of additional GAS strains associated with specific clinical syndromes may identify additional novel phage-encoded virulence factors. Toxins and other virulence factors encoded by GAS phages can be divided into two main groups, including pyrogenic toxin superantigens (PTSAgs) and non-PTSAgs. It is well known that GAS prophages encode extracellular proteins that interact with the host during infection and contribute to pathogenesis. Only recently has the significant link between phage biology, genome diversity, and streptococcal pathogenesis been fully appreciated. Continued investigations of streptococcal phage biology will undoubtedly reveal additional significant contributions that these mobile genetic elements have in bacterial pathogenesis and human disease.