Clinical MRSA isolates from skin and soft tissue infections show increased in vitro production of phenol soluble modulins

Abstract

Phenol-soluble modulins (PSMs) are amphipathic, pro-inflammatory proteins secreted by most Staphylococcus aureus isolates. This study tested the hypothesis that invitro PSM production levels are associated with specific clinical phenotypes. 177 methicillin-resistant S. aureus (MRSA) isolates from infective endocarditis (IE), skin and soft tissue infection (SSTI), and hospital-acquired/ventilator-associated pneumonia (HAP) were matched by geographic origin, then genotyped using spa-typing. Invitro PSM production was measured by high performance liquid chromatography/mass spectrometry. Statistical analysis was performed using Chi-squared or Kruskal-Wallis tests as appropriate. Spa type 1 was significantly more common in SSTI isolates (62.7% SSTI; 1.7% IE; 16.9% HAP; p<0.0001) while HAP and IE isolates were more commonly spa type 2 (0% SSTI; 37.3% IE; 40.7% HAP; p<0.0001). USA300 isolates produced the highest levels of PSMs invitro. SSTI isolates produced significantly higher quantities of PSMα1-4, PSMβ1, and δ-toxin than other isolates (p<0.001). These findings persisted when USA300 isolates were excluded from analysis. Increased invitro production of PSMs is associated with an SSTI clinical source. This significant association persisted after exclusion of USA300 genotype isolates from analysis, suggesting that PSMs play a particularly important role in the pathogenesis of SSTI as compared to other infection types.