Detection of streptococcal pyrogenic exotoxin genes by a nested polymerase chain reaction

Abstract

Severe invasive disease associated with group A Streptococcus (GAS) has recently increased in frequency. Isolates of GAS from normally sterile sites were examined for the streptococcal pyrogenic exotoxin genes spe A, spe B and spe C to determine if they play a role in this disease. Four primers for each gene were used in a nested polymerase chain reaction (PCR) configuration. The first PCR generated fragments of 818, 1106, and 801 bp, respectively, for the extotoxin genes. The second PCR generated fragments of 500, 912 and 654 bp for the spe A, spe B and spe C genes using the fragments from the first PCR as template. Of 62 strains tested, 35 (56%) contained the spe A gene, and 17 (27%) contained the spe C gene. All GAS strains studied, regardless of disease association, contained the spe B gene. These data corroborate accumulating evidence that the genes encoding pyrogenic exotoxin types B and C are not associated with severe invasive streptococcal illness including streptococcal toxic shock-like syndrome. This PCR-based gene detection system has clinical and epidemiologic applications because of its ease of performance, non-isotope labelling, high specificity and sensitivity, and lack of requirement for purified DNA.