M. OBERLE¹, A. HASLER¹, C. OTTIGER¹, H. FANKHAUSER<sup>1

1</sup>Medizinische Mikrobiologie, Institut für Labormedizin, Kantonsspital Aarau, 5001 Aarau, Schweiz

Background: Panton-Valentine leucocidin (PVL) is a toxin responsible for increased severity in Staphylococcus aureus infections. PVL is encoded by the two cotranscribed genes lukS-PV and lukF-PV and is carried on a bacteriophage. Diagnosis for the presence of the PVL genes in clinical S. aureus isolates is rarely done. Therefore the prevalence of PVL in S. aureus from clinical isolates and from healthy carriers is largely unknown in Switzerland. The aim of this study was to measure the frequency of PVL positive S. aureus isolates in healthy Swiss carriers and in clinical specimens. Methods: S. aureus isolates from diverse clinical samples were selected retrospectively. Nasal swaps from healthy individuals were collected, and S. aureus isolates were analysed for PVL. Detection of the lukS-PV/ lukF-PV genes was done with real time PCR (RIDA PVL kit, rBiopharm on a LighCycler 2.0, Roche). Results: Sixty S. aureus carriers from 197 nasal swabs of healthy individuals were identified. No PVL-positive S. aureus was found among the healthy carries. Eighteen (30%) of the 60 clinical isolates were tested positive for PVL. Eleven isolates derived from wound swabs, six from biopsies and sterile fluids and one was isolated from a blood culture. Interestingly, one third (six) of the PVL-positive isolates were Methicillin susceptible S. aureus (MSSA) and the remaining (12) were MRSA. Conclusions: The prevalence of PVL-positive S. aureus among the healthy Swiss population (0 out of 60) seems to be very low in comparison to the clinical isolates (p <0.001). This suggests that former healthy carriers of PVL have a high risk for severe S. aureus infections. Of interest is that not only MRSA but also MSSA do contain the PVL. Such isolates may worsen the clinical outcome and may require an adjusted treatment. Nevertheless, the detection of the lukS-PV/ lukF-PV genes is seldom asked in clinical microbiology laboratories suggesting underestimation of PVL-positive MSSA’s.