Evaluation of the R-Biopharm RIDAA®GENE Panton-Valentine leukocidin (PVL) kit for the detection of Staphylococcus aureus PVL from pus samples

Staphylococcus aureus Panton-Valentine leukocidin (PVL) is associated with primary skin and soft-tissue infections (SSTI). We aimed to divert the RIDAA (R) GENE PVL kit (RBiopharm) from its intended use on cultures to the detection of PVL-encoding genes directly from pus samples. Performance was compared with that of the in-house PCR method developed by the French National Reference Centre for Staphylococci. From June 2013 to May 2014, pus samples from S. aureus SSTI were tested. Our in-house PCR was performed on parallel cultures as the gold standard, while the RIDAA (R) GENE PVL assay was used directly on pus samples from the sterile container, or a swab or an Eswab previously dipped in the pus. The kit specificity was also evaluated with pus samples that grew Streptococcus pyogenes. S. aureus reference strains harboring PVL-encoding genes, including known polymorphisms, were also tested. A total of 56 S. aureus-containing pus samples (28 PVL + and 28 PVL-) were collected and analyzed. Sensitivity and specificity of the commercial kit were 96.4 % and 100 % respectively, with equal performance whether tested directly from the sterile container or the Eswab. Sensitivity was lower (67.9 %) when the test was performed from a regular SSTI swab. None of the Streptococcus pyogenes pus samples scored positive (n = 5). Specificity was assessed using reference strains (n = 14); in all strains the PVL gene was correctly detected. This study identified the RIDAA (R) GENE PVL kit as an efficient, sensitive, and specific tool for the rapid detection of PVL-encoding genes in pus samples.