Extension of the Lancefield classification for group A streptococci by addition of 22 new M protein gene sequence types from clinical isolates: emm103 to emm124.

Classic M protein serotyping has been invaluable during the past 60 years for the determination of relationships between different group A streptococci (GAS) strains and the varied clinical manifestations inflicted by these organisms worldwide. Nonetheless, during the past 20 years, the difficulties of continued expansion of the serology-based Lancefield classification scheme for GAS have become increasingly apparent. By use of a less demanding sequence-based methodology that closely adheres to previously established strain criteria while being predictive of known M protein serotypes, we recently added types emm94-emm102 to the Lancefield scheme. Continued expansion by the addition of types emm103 to emm124 are now proposed. As with types emm94-emm102, each of these new emm types was represented by multiple independent isolates recovered from serious disease manifestations, each was M protein nontypeable with all typing sera stocks available to international GAS reference laboratories, and each demonstrated antiphagocytic properties in vitro by multiplying in normal human blood.