Clonal associations among Staphylococcus aureus isolates from various sites of infection

A molecular epidemiological analysis was undertaken to identify lineages of Staphylococcus aureus that may be disproportionately associated with infec tion. pulsed-held gel electrophoresis analysis of 405 S. aureus clinical is olates collected from various infection types and geographic locations was performed. Five distinct S. aureus lineages (SALs 1, 2, 4, 5, and 6) were i dentified, which accounted for 19.01, 9.14, 22.72, 10.12, and 4.69% of isol ates, respectively. In addition, 85 lineages which occurred with frequencie s of <2.5% were identified and were termed "sporadic." The most prevalent l ineage was methicillin-resistant S. aureus (SAL 4). The second most prevale nt lineage, SAL 1, was also isolated at a high frequency from the anterior nares of healthy volunteers, suggesting that its prevalence among clinical isolates may be a consequence of high carriage rates in humans. Gene-specif ic PCR was carried out to detect genes for a number of staphylococcal virul ence traits, tst and cna were found to be significantly associated with pre valent lineages compared to sporadic lineages. When specific infection site s were examined, SAL 4 was significantly associated with respiratory tract infection, while SAL 2 was enriched among blood isolates. SAL 1 and SAL 5 w ere clonally related to SALs shown by others to be widespread in the clinic al isolate population. We conclude from this study that at least five phylo genetic lineages of S. aureus are highly prevalent and widely distributed a mong clinical isolates. The traits that confer on these lineages a propensi ty to infect may suggest novel approaches to antistaphylococcal therapy.