Polymorphisms of agr locus correspond to distinct genetic patterns of virulence in Staphylococcus aureus clinical isolates from orthopedic implant infections.

Staphylococcus aureus is the leading etiologic agent of orthopedic implant infections. It is endowed with the accessory gene regulator (agr) locus that modulates expression of many virulence genes. Four allelic groups of agr have been recognized within this bacterial species. Here, 200 S. aureus isolates from orthopedic implant infections, typed at the start depending on their agr group, were screened for the presence of adhesin and leukotoxin genes. Interestingly, specific virulence gene patterns emerged in association with agr groups. The most frequently observed agr groups, agr I and agr II, were associated with the presence of sdrE, fib (agr II more than agr I), fnbB (agr I more than agr II), and lukE/lukD (agr II more than agr I). The third more frequent agr group, agr III, differed clearly from agr I and II, exhibiting high prevalence of bbp, generally not harbored by agr I and II, and copresence of bbp with cna, whereas high prevalence of the tandem sdrE/fib marked definitely agr II (91% of agr II isolates), and, though less strictly, agr I, in which prevailed the peculiar fib/fnbB pattern. The only four isolates belonging to agr IV showed full copresence of bbp with fib. Results point out distinct patterns of virulence genes, which underlie distinct evolutive strategies associated to agr groups in S. aureus causing orthopedic implant infections