lukSF-PV in Staphylococcus aureus keratitis isolates and association with clinical outcome

To determine the prevalence, genetic diversity, and clinical relevance of the lukSF-PV gene, encoding the bacterial toxin Panton-Valentine leukocidin, in Staphylococcus aureus isolates from cases of bacterial keratitis in the United Kingdom. Multiplex PCRs investigating carriage of lukSF-PV and mecA were performed on S. aureus isolates from patients. The lukSF-PV operon was sequenced to investigate its diversity, and multilocus sequence typing to test for a clonal relationship between lukSF-PV isolates. Antimicrobial minimum inhibitory concentrations (MICs) and clinical outcome data were compared for isolates characterized as lukSF-PV+ve, mecA+ve, and lukSF-PV/mecA-ve. Of 95 isolates, 9 (9.5%) were lukSF-PV+ve, 9 (9.5%) mecA+ve, and 1 was positive for both. Five single nucleotide polymorphisms were found in lukSF-PV genes of seven strains. There was no significant difference between the MICs of lukSF-PV/mecA-ve and lukSF-PV+ve isolates to the antimicrobials tested, except for tigecycline (P < 0.05). The mecA+ve isolates had significantly higher mean MICs to meropenem and fluoroquinolones (P < 0.05). There were nonsignificant trends for healing and treatment times, ulcer and scar size, and overall clinical score to be greater in the lukSF-PV+ve group (P < 0.05). The proportion of patients, however, who required surgery was significantly greater among patients with lukSF-PV+ve isolates with an odds ratio of 7.8 (95% CI 1-42, P = 0.018) for patients requiring surgery. lukSF-PV+ve isolates were associated with a trend to worse clinical outcome and more surgical interventions, with an effect unrelated to MICs. This suggests that lukSF-PV may be an important virulence factor in S. aureus-associated keratitis.