Rapid molecular genetic subtyping of serotype M1 group A Streptococcus strains

Serotype M1 group A Streptococcus, the most common cause of invasive diseas e in many case series, generally have resisted extensive molecular subtypin g by standard techniques (e.g., multilocus enzyme electrophoresis, pulsed-f ield gel electrophoresis). We used automated sequencing of the sic gene enc oding streptococcal inhibitor of complement and of a region of the chromoso me with direct repeat sequences to unambiguously differentiate 30 M1 isolat es recovered from 28 patients in Texas with invasive disease episodes tempo rally clustered and thought to represent an outbreak. Sequencing of the emm gene was less useful for M1 strain differentiation, and restriction fragme nt length polymorphism analysis with IS1548 or IS1562 as Southern hybridiza tion probes did not provide epidemiologically useful subtyping information. Sequence polymorphism in the direct repeat region of the chromosome and IS 1548 profiling data support the hypothesis that MI organisms have two main evolutionary lineages marked by the presence or absence of the speA2 allel e encoding streptococcal pyrogenic exotoxin A2.