Streptococcus pyogenes pharyngitis: characterization of strains by multilocus enzyme genotype, M and T protein serotype, and pyrogenic exotoxin gene probing.

Multilocus enzyme electrophoresis, serological characterization of M and T proteins, and probing for pyrogenic exotoxin A and C genes were used to investigate the bacteriologic epidemiology of strains of Streptococcus pyogenes recovered primarily from patients with recurrent pharyngitis. A total of 164 strains recovered from individuals living in nine states of the United States was analyzed. Two-thirds of the patients in our sample were infected with the homologous strain following antibiotic therapy and presumably represented treatment failures, whereas the other one-third of the patients were infected with a heterologous strain after therapy and probably represented reinfections. Multilocus enzyme electrophoresis was as efficacious in strain discrimination as serologic typing techniques were and, in addition, successfully characterized all organisms that were serologically nontypeable. Two clones of S. pyogenes responsible for most of the episodes of toxic shock-like syndrome in the United States are geographically widespread, but they vary by locality in the frequency of their occurrence. Compared with a sample of strains cultured from patients whose pharyngeal infections were eliminated by antimicrobial therapy, these two clones were statistically overrepresented among organisms that cause recurrent pharyngitis.