Virulence-associated genes of Staphylococcus aureus isolates from soft tissue infections in Alpine chamois

Background Staphylococcus aureus virulence pattern, antimicrobial resistance profile and host specialization are of great concern in domestic animals that can act as reservoir for transient carriers of zoonotic [1] and human strains [2]. In regards to free-living wild ruminants, a low prevalence of methicillin resistant S. aureus (MRSA) was recently reported in healthy Iberian ibex (Capra pyrenaica hispanica) and red deer (Cervus elaphus) [3]. Materials and methods S. aureus isolates were obtained from two subjects that were euthanised by gamekeepers due to a walking impairment in the north-western Italian Alps (Verbano Cusio Ossola province) in autumn 2011. The subjects, a kid and a three year old male, showed good body condition and a regular process of molt. The post-mortem examination confirmed good kidney fat deposition and normal gastric content. No macroscopic lesions were observed in the kid. Acute fibrinous pericarditis, liver steatosis and an enlarged retromandibular lymph node affected by an abscess were observed in the adult chamois. Samples for bacteriological analysis were collected from the kid’s nasal cavities and organs (brain, lung, liver, spleen and kidney) and from the adult’s abscess. PCR analysis was performed on S.aureus isolates targeting virulence-associated genes using previously described protocols (nuc, sea, sec, sed, seg, seh, sei, sej, sek, and sel [4]; coa, clfA, spa, tst, seb, see, eta, and etb [5]; leukE [6]; LukS–LukF/ PV {PVL} and mecA [7]; sak, fmtB, scn, and chp [2]; LukE–LukD and LukM [8]; cna [9]). Results and discussion S. aureus soft-tissue infections were observed in both subjects and a colonization of nasal mucosa was also confirmed. S. aureus was isolated from nasal mucosa and the liver of the kid and from the abscess of adult chamois. A large set of enterotoxin genes (sea, sec, seg, sei, sel), rare in domestic ruminants [6, 10, 11], were identified from S. aureus isolates, harbouring from two (nasal, abscess isolates) to five different genes (liver isolate). The abscess isolate was also positive for leukotoxin and toxic shock syndrome toxin (tst) genes. None of the isolates harboured genes encoding for exfoliative toxins A and B (eta, etb) and Panton-Valentine Leukocidin (LukS–LukF/PVpvl). All S. aureus isolates were positive for spa, coa, leukE, clfA, nuc, fmtB, cna, sak, scn and chp genes. To our knowledge, data on S. aureus virulence pattern have not yet been recorded in chamois and in other wild ruminants with which our data can be compared to. However, the immune evasion gene cluster, rare in animal isolates and highly prevalent in humans [2] was detected in all the isolates. A matter of great concern is the presence of the tst gene, located, with sec and sel genes, on a mobile genetic element called the pathogenicity island, coding for a toxin that damages host tissues and provokes toxic shock syndrome in humans. Overall, although the data from this study are inadequate to draw any association between the S. aureus virulence profile and the clinical debility of these animals, peculiar and rare virulence profiles were detected. Perspective and future research priorities The antimicrobial resistance profile and genotype characterization of the isolates are ongoing. A larger number of isolates from wild and domestic species need to be investigated in order to understand host specificity and to assess the zoonotic or anthropo-zoonotic potential of S. aureus. Acknowledgements We wish to thank the Corpo di Polizia Provinciale di Verbania and Ente Parco Nazionale Val Grande for field support.