lukSF-PVinStaphylococcus aureusKeratitis Isolates and Association With Clinical Outcome

Abstract

PURPOSE.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.METHODS. 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-PVþve, mecAþve, and lukSF-PV/mecA-ve. RESULTS.Of 95 isolates, 9 (9.5%) were lukSF-PVþve, 9 (9.5%) mecAþve, 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-PVþve isolates to the antimicrobials tested, except for tigecycline (P < 0.05). The mecAþve 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-PVþve group (P < 0.05). The proportion of patients, however, who required surgery was significantly greater among patients with lukSF-PVþve isolates with an odds ratio of 7.8 (95% CI 1-42, P ¼ 0.018) for patients requiring surgery.CONCLUSIONS. lukSF-PVþve 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.Keywords: keratitis, Panton-Valentine leukocidin, Staphylococcus aureus keratitis T he pathogenicity of Staphylococcus aureus is mediated by a multitude of secreted virulence factors, such as bacterial surface adhesins, immune evasion proteins, and toxins. PantonValentine leukocidin (PVL) is a pore-forming toxin produced by S. aureus.1 It is a bicomponent toxin that consists of the polypeptides LukS-PV and LukF-PV. 2 The cognate LukS-PV and LukF-PV bind to neutrophils, monocytes, and macrophages, but not to lymphocytes.3 Following the binding of monomers of LukS-PV and LukF-PV, further monomers attach to the cell wall forming a heptameric structure that forms a pore in the host cell surface. 2,4 This pore formation results in leukocyte cell death and the release of inflammatory cytokines. 3 The involvement, however, of PVL in the virulence of S. aureus is equivocal and its link with clinical outcome remains uncertain. In vivo studies have produced conflicting data. Murine models of S. aureus infection have shown that the absence of PVL results in an increase in virulence, 5-8 whereas studies in rabbits indicate that the presence of PVL increases the virulence of S. aureus.9-11 These discrepancies could, however, be attributed to differences in the immunology of the models. 11 Mo...

An Evaluation of Staphylococci from Ocular Surface Infections Treated Empirically with Topical Besifloxacin: Antibiotic Resistance, Molecular Characteristics, and Clinical Outcomes

“…Pending results, a secondary objective was to begin to formulate an ocular breakpoint for this fluoroquinolone. To date, few studies have examined antibiotic resistance profiles and genotypic characteristics of staphylococci from ocular infections in association with clinical outcome data [27][28][29], and to our knowledge, none have reported on how molecular or resistance features of ocular staphylococci might correlate with the clinical efficacy of a specific antibiotic treatment.…”

Ex vivo rabbit and human corneas as models for bacterial and fungal keratitis

“… We did not observe any ulceration or corneal edema. This is because ex vivo corneas lack inflammatory cells that are primarily responsible for epithelial ulceration [ 32 ], stromal polymorphonuclear neutrophil (PMN) infiltration [ 34 – 36 ], and ulcer formation [ 37 ] seen in clinical S. aureus infection. Compared to the S. aureus model, P. aeruginosa -infected corneas yielded a greater number of CFU/cornea and were seen infiltrating the entire cornea, despite having the same inoculum.…”

The Pathogenesis of Staphylococcus aureus Eye Infections

“…PVL is another two-component toxin composed of an F and an S protein that is produced mainly by community-associated MRSA strains (CA-MRSA), which are frequently found as the cause of skin and soft-tissue infections and are recognized as important agents of keratitis [ 100 , 101 , 102 , 103 ]. One study has determined that PVL producing strains likely cause a more severe form of keratitis, a form that requires surgery more often than keratitis caused by non-PVL producing strains [ 104 ]. Corneal infection of mice with three parent strains or three PVL knockout strains were compared [ 94 ].…”