Electronic Thesis and Dissertation Repository


Master of Science


Microbiology and Immunology


McCormick, John K.


Pathogenic streptococci have evolved specific systems to eliminate bacterial competitors within their biological niche. In microbial environments, niche competition is often driven by the production of short antimicrobial peptides called bacteriocins; this provides a mechanism by which Streptococcus pyogenes may compete for ecological stability and establish infection. Recent findings from our laboratory have identified two novel Class IIb bacteriocin systems – Streptococcus pyogenes bacteriocin (Spb) JK and MN in the M18 serotype S. pyogenes strain MGAS8232 – that may contribute to nasopharyngeal infection. Here, we show that galactose and CO2 are distinct regulatory cues which induce antimicrobial activity. Under these conditions, bacteriocin-producing strains inhibit the growth of other Gram-positive bacteria in vitro. We also demonstrate that acute infection in the nasopharynx of mice is dependent on the expression of at least one functional bacteriocin system. When mice are challenged intranasally with a double-bacteriocin knockout, the bacterial burden is dramatically reduced compared to the wild-type and single bacteriocin mutant controls. Furthermore, we show that nasal coinfection with S. pyogenes wild-type and spbJKMN- results in a wild-type dominant population, suggesting that bacteriocins enhance bacterial fitness in a polymicrobial environment. Taken together, these observations demonstrate that S. pyogenes secretes bacteriocins which contribute to the establishment of nasopharyngeal infection.