A single clone of Staphylococcus aureus causes the majority of cases of toxic shock syndrome.

Genetic relationships among 315 isolates of the bacterium Staphylococcus aureus expressing toxic shock syndrome toxin-1 (TSST-1) recovered primarily from humans with toxic shock syndrome (TSS) in five countries on two continents were determined by analyzing electrophoretically demonstrable allelic variation at 20 chromosomal enzyme loci. Forty-nine distinctive electrophoretic types (ETs), representing multilocus enzyme genotypes, were identified. Cluster analysis of the ETs revealed two major phylogenetic divisions separated at a genetic distance of 0.35 and seven branches diverging from one another at distances greater than or equal to 0.20. A single clone (ET 41) accounted for 88% of cases of TSS with a female urogenital focus and 53% of TSS cases involving nonurogenital (predominantly wound) infections. With few exceptions, strains representing different phylogenetic lines had characteristic TSST-1 gene (tst) restriction fragment length polymorphism patterns obtained by digestion of genomic DNA with Cla I. Strains recovered from ovine and bovine hosts with mastitis were genotypically distinct from the major human TSS clone. The expression of TSST-1 in cell lineages representing the total breadth of multilocus genotypic diversity in the species S. aureus as a whole is interpreted as evidence that the TSST-1 gene is evolutionarily old. The recovery of a single clone from the majority of individuals afflicted with TSS having a urogenital focus and from the genital tract of a large proportion of asymptomatic female carriers strongly suggests that this clone is especially well adapted for colonization of these anatomic sites.