AN ANALYSIS INTO THE FUNCTIONING OF THE S. INTERMEDIUS B196 STREPTOCOCCUS INVASION LOCUS

Abstract

The Streptococcus Anginosus Group (SAG) is a group of Gram-positive cocci which require carbon dioxide to grow. They are commensal members of the healthy upper respiratory, gastrointestinal and female urogenital tract; however, they are most commonly known as major pathogens in brain and liver abscesses, forming both mono- and polymicrobial infections. The Streptococcus invasion locus (sil), first identified as a virulence factor in Group A Streptococcus (GAS), has recently been identified in the SAG. The sil locus in GAS is a two component quorum-sensing system composed of three operons: silAB, coding for a two component system; silE/D/CR, coding for an ABC transporter and a signal peptide, and silC, which overlaps silCR on the opposite strand. The presence of exogenous SilCR activates SilA, which in turn upregulates the transcription of the silE/D/CR operon. In the SAG, however, silCR and silED have distinct promoters, and the SAG sil system lacks the silC gene. In this study, I examined the transcriptional dynamics of the sil system in S. intermedius B196. I determined that SilA is the major regulator of the genes in the sil system, being one of the first genes of the system to be expressed, and likely upregulates its own transcription. I also found evidence suggesting that, despite having its own promoter, silCR transcription may still be driven by the silED promoter. I also found evidence that suggests silED may be responsible for the export and/or processing of bacteriocins targeting closely related species or strains.