Rapid molecular genetic subtyping of serotype M1 group A Streptococcus strains.

Molecular genetic approaches that differen-tiate isolates of a pathogenic microbial specieshave revolutionized contemporary epidemiologicinvestigations of putative disease outbreaks. Thehuman gram-positive bacterium group AStreptococcus (GAS) has more than 80 M-proteinserotypes, but isolates expressing the M1serotype are disproportionately representedamong invasive disease episodes in most caseseries (1). M1 organisms also commonly causepharyngitis. For reasons that are unknown, M1isolates and organisms expressing other Mserologic types can undergo rapid temporalvariation in disease frequency and severity (1).Serotype M1 isolates have been studied byseveral molecular typing approaches, includingmultilocus enzyme electrophoresis; pulsed-fieldgel electrophoresis; rRNA gene polymorphismtyping (ribotyping); random amplified polymor-phic DNA analysis; and sequencing of the genesencoding streptokinase, C5a peptidase, M protein,hyaluronidase, and pyrogenic exotoxin A, B, andC (1-5). The common theme of these analyses isthat most M1 isolates cultured from patientswith invasive disease episodes are closely alliedin overall chromosomal relationship as aconsequence of sharing a recent commonancestor (1,3,5). Lack of readily detectablechromosomal variation has limited insights onthe molecular origin of new virulent strains,velocity of strain spread in human populations,and association of genetic subtypes with certainclinical syndromes, including necrotizing fasciitisand acute rheumatic fever.Recently, Akesson et al. (6) identified a GASextracellular protein made by M1 strains thatinhibits human complement. This streptococcalinhibitor of complement (Sic) protein isincorporated into the membrane-attack complex(C5b-C9) and inhibits target cell lysis by anundetermined mechanism. Analysis of molecu-lar diversity among 16 M1 GAS isolates frompatients with pharyngitis identified seven allelesof the sic gene (7). The high level of sicpolymorphism was unanticipated, given thatother methods of molecular analysis had failed toidentify substantial variation among M1 isolates