Is Panton-Valentine leucocidin associated with the pathogenesis of Staphylococcus aureus bacteraemia in the UK?

Background: The morbidity and mortality associated with Panton-Valentine leucocidin (PVL)-positive Staphylococcus aureus suggest that this toxin is a key marker of disease severity. Nevertheless, the importance of PVL in the pathogenesis of primary bacteraemia caused by S. aureus is uncertain. We have determined the prevalence of PVL-encoding genes among isolates of S. aureus from bacteraemic patients.

Methods: Consecutive bacteraemia isolates of S. aureus (n=244) from patients hospitalized in 25 centres in the UK and Ireland during 2005 were screened for PVL and mecA genes. PVL-positive isolates were characterized by toxin gene profiling, PFGE, spa-typing and MIC determinations for a range of antimicrobials.

Results: Four out of 244 isolates (1.6%) were PVL-positive and susceptible to oxacillin [methicillin-susceptible S. aureus (MSSA)]. Eighty-eight out of 244 (36%) were oxacillin-resistant (methicillin-resistant S. aureus), but none was PVL-positive. The four patients (two males: 30 and 33 years; two females: 62 and 80 years) had infection foci of: skin and soft tissue, unknown, indwelling line, and surgical site, and were located at one centre in Wales, one in England and two in Ireland. One of four PVL-positive isolates was resistant to penicillin and fusidic acid, the remainder were susceptible to all antibiotics tested. Genotypic analyses showed that the four isolates represented three distinct strains; the two isolates from Ireland were related.

Conclusions: We found that 1.6% of S. aureus (all MSSA) from bacteraemic patients were PVL-positive. This low incidence suggests that PVL-positive S. aureus are of no particular significance as causative agents of S. aureus bacteraemia.