Virulence Gene Expression in Human Community- Acquired Staphylococcus aureus Infection

(See the editorial commentary by Chambers, on pages 291–3.) Isolates of methicillin-resistant Staphylococcus aureus (MRSA) were once linked uniformly with hospital-associated infections; however, community-acquired MRSA (CA-MRSA) now represents an emerging threat worldwide. To examine the association of differential virulence gene expression with outcomes of human infec-tion, we measured transcript levels of target staphylococcal genes directly in clinical samples from children with active known or suspected CA-MRSA infections. Virulence genes encoding secreted toxins, including Panton-Valentine leukocidin, were highly expressed during superficial and invasive CA-MRSA infections. In contrast, increased expression of surface-associated protein A was linked only with invasive disease. Comparisons with laboratory-grown corresponding clinical isolates revealed that tissue-specific expression profiles reflect the activ-ity of the staphylococcal accessory gene regulator during human infection. These results represent the first dem-onstration of staphylococcal gene expression and regulation directly in human tissue. Such analysis will help to unravel the complex interactions between CA-MRSA and its host environmental niches during disease development. Staphylococcus aureus is a persistent human pathogen that is responsible for a range of diseases that vary widel