The primary objective of the proposed research is to elucidate the clonal population structure and genetic relationships among unusually virulent strains of Streptococcus pyogenes, with special reference to organisms expressing pyrogenic exotoxin serotype A and/or C that very recently have been recovered in the United States and elsewhere from cases of toxic shock-like syndrome and other severe invasive diseases. Multilocus enzyme electrophoresis, which detects allelic variation in metabolic enzyme-encoding chromosomal genes, will be used to identify clones and assess overall chromosomal relatedness of pyrogenic exotoxin- expressing strains to isolates recovered from asymptomatic carriers, and other disease syndromes such as pharyngitis, glomerulonephritis, cellulitis, rheumatic fever, and scarlet fever. The second goal is to determine if pyrogenic exotoxin-expressing strains (especially those producing serotype M1 protein) recovered from patients in many European countries - where the increase in disease frequency and severity preceded that recorded in the United States - are clonally related to isolates recently causing toxic shock-like syndrome and other invasive diseases in this country. A third goal is to assess, at the molecular level, the extent to which horizontal transfer and recombination has contributed to the phylogenetic widespread occurrence of two related bacteriophage-borne pyrogenic exotoxin genes (speA and speC), and perhaps, to the origin of contemporary unusually virulent cell lineages. The genetic relationships among toxin-producing chromosomal genotypes revealed by multilocus enzyme electrophoresis will be used to provide a rational population genetic framework for relatively large-scale analysis of sequence divergence in speA and speC following amplification with the polymerase chain reaction. Data generated in the accomplishment of the third goal will be used to provide insight into the evolutionary forces molding the nature and extent of exotoxin sequence variation.