Abstract
The Streptococcus Invasion Locus (Sil) was first described in Streptococcus pyogenes and Streptococcus pneumoniae, where it has been implicated in virulence. The two-component peptide signaling system consists of the SilA response regulator and SilB histidine kinase along with the SilCR signaling peptide and SilD/E export/processing proteins. The presence of an associated bacteriocin region suggests this system may play a role in competitive interactions with other microbes. Comparative analysis of 42 Streptococcus Anginosus/Milleri Group (SAG) genomes reveals this to be a hot spot for genomic variability. A cluster of bacteriocin/immunity genes is found adjacent to the sil system in most SAG isolates (typically 6–10 per strain). In addition, there were two distinct SilCR peptides identified in this group, denoted here as SilCRSAG-A and SilCRSAG-B, with corresponding alleles in silB. Our analysis of the 42 sil loci showed that SilCRSAG-A is only found in Streptococcus intermedius while all three species can carry SilCRSAG-B. In S. intermedius B196, a putative SilA operator is located upstream of bacteriocin gene clusters, implicating the sil system in regulation of microbe–microbe interactions at mucosal surfaces where the group resides. We demonstrate that S. intermedius B196 responds to its cognate SilCRSAG-A, and, less effectively, to SilCRSAG-B released by other Anginosus group members, to produce putative bacteriocins and inhibit the growth of a sensitive strain of S. constellatus.
Highlights
The Streptococcus Anginosus/Milleri Group (SAG) is a group of three distinct yet closely related species: S. anginosus, S. constellatus, and S. intermedius
The species S. anginosus is divided into S. anginosus subsp. anginosus and S. anginosus subsp. whileyi while the species S. constellatus is divided into S. constellatus subsp. constellatus, S. constellatus subsp. pharyngis and S. constellatus subsp. viborgensis (Jensen et al, 2013)
A 100 μL of overnight broth culture of S. constellatus M505 was added to 5 mL molten Top agar and inverted three times before pouring onto the agar plates with S. intermedius spots
Summary
The Streptococcus Anginosus/Milleri Group (SAG) is a group of three distinct yet closely related species: S. anginosus, S. constellatus, and S. intermedius. Streptococcus Anginosus Group sil Locus as the gastrointestinal and urogenital tracts (Poole and Wilson, 1979; Whiley et al, 1992; Jacobs et al, 1995) They are important pyogenic pathogens involved in empyema and soft tissue abscesses (Ruoff, 1988; Whiley et al, 1992; Coman et al, 1995; Laupland et al, 2006; Ripley et al, 2006; Siegman-Igra et al, 2012; Asam and Spellerberg, 2014) as well as infections of the lower airways (Shinzato and Saito, 1995; Parkins et al, 2008; Sibley et al, 2008). They have been associated with more invasive pyogenic infections than Group A and Group B Streptococcus combined (Laupland et al, 2006; Siegman-Igra et al, 2012)
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