Streptococcal pyrogenic exotoxin G gene in blood and pharyngeal isolates of Streptococcus dysgalactiae subspecies equisimilis has a limited role in pathogenesis.

BACKGROUND: Streptococcus dysgalactiae subspecies equisimilis (SE) causes human infections that clinically resemble infections due to Streptococcus pyogenes (SP). SE expresses several virulence determinants initially identified in SP, including genes encoding streptococcal pyrogenic exotoxins. SE isolates from patients with toxic shock syndrome were found to harbor a gene designated spegg, which is similar to the SP pyrogenic exotoxin-G gene, termed speG. Other streptococcal pyrogenic exotoxins known to exist in SP were not detected.

METHODS: To determine the prevalence of the superantigen gene, spegg, we examined 65 invasive SE from patients presenting from 1989 to 2008 with bacteremia secondary to a variety of illnesses including two patients who fulfilled the criteria for toxic shock syndrome, in comparison with 46 noninvasive pharyngeal isolates. All isolates were tested for the presence of spegg by polymerase chain reaction. Forty-four of the 65 blood isolates were also characterized by emm typing.

RESULTS: spegg was identified in 49.2% and 69.5% of the blood and pharyngeal isolates, respectively. emm typing revealed the presence of 13 distinct types. There was no association between clinical presentation and the presence of spegg. We found an association between the presence of spegg and the emm type (p < 0.001). The emm types stG485 and stG840 were more frequent among spegg positive isolates, and stG4222, stG6, and stG166b were associated with spegg negative isolates.

CONCLUSION: We found a high prevalence of spegg in invasive and noninvasive SE isolates, associated with specific emm types. Our finding suggests that this gene does not have a role in the pathogenesis of bacteremia.