GENETIC CORRELATES OF THROAT AND SKIN ISOLATES OF GROUP-A STREPTOCOCCI

The existence of discrete populations of throat and skin strains of gr oup A streptococci has long been recognized; however, a molecular basi s for this distinction is not known. The emm gene structure was analyz ed for 105 isolates obtained from patients with well-defined group A s treptococcal diseases: uncomplicated pharyngitis, impetigo, and acute rheumatic fever. Four emm gene subfamily forms, defined by nucleotide sequence differences in regions encoding the peptidoglycan-spanning do main of M and M-like surface proteins, were found to exist in five dif ferent chromosomal patterns among naturally occurring isolates. Strong correlations were made between disease and the number and arrangement of emm subfamily genes, These findings provide a genetic basis for th e historical references to ''throat,'' ''skin,'' and ''rheumatogenic'' types.