New sequence type of Methicillin Resistant Staphylococcus Aureus (MRSA) from liver infection in an alpine chamois

Methicillin resistant Staphylococcus aureus (MRSA) is a well-known cause of skin and soft tissue infections in humans, both in hospital and community settings. Companion animals (dogs, cats, horses) can experience such infections as the consequence of penetrating wound and surgery. Nasal and skin carriage are proved predisposing factors. Production animals are frequently healthy carriers of the Livestock-associated sequence type 398 (ST398) at nasal and other body sites level. Cattle mastitis can be caused by MRSA. Wild animals are thought to be less exposed to MRSA due to presumed uncontaminated environment and lack of antibiotics selective pressure. Yet, MRSA was recently detected in free-ranging species in aquatic and terrestrial environment in North America. In wild ruminant, a low prevalence of ST398 MRSA carriage was recently reported in healthy Iberian Ibex and red deer. S. aureus isolates included were obtained from a kid chamois (Rupicapra r. rupicapra), that was euthanized by gamekeepers, due to walking impairment and painful status, in autumn 2011 in north-western Italian Alps. A post-mortem examination was performed. Samples for bacteriological analysis were swabs collected from nasal cavities and organs (brain, lung, liver, spleen and kidney). After an overnight incubation in Brain Hearth Infusion at 37°C, 100 μl of the preenrichment were plated onto 5% sheep blood agar. Bacteria were identified according to colony morphology, hemolysis, Gram-stain andreaction to catalase and coagulase tests. They underwent confirmation by PCR, antimicrobial susceptibility test and typing. S. aureus was isolated from nasal mucosa and liver. No other relevant bacterial growth was detected. At the post-mortem examination, animal showed a good kidney fat deposit and regular contents of stomach compartments. No macroscopic lesions were observed. PCR revealed mecA gene in the liver isolate. Antimicrobial susceptibility test confirmed resistance to all beta-lactams tested (amoxicillin-clavulanic acid, penicillin, ampicillin, ceftiofur, cefoxitin) besides resistance to fluoroquinolones (ciprofloxacin, enrofloxacin, marbofloxacin) and susceptibility to tetracycline. This resistance profile is unusual for MRSA commonly isolated from livestock and poultry, due to coexistence of sensibility to tetracycline and resistance to fluoroquinolones. No antimicrobial resistance was detected in the nasal isolate. Multi Locus Sequence Typing revealed two different new ST, namely ST 2716 for MRSA from the liver and ST2715 for nasal mucosa isolate. This accidental isolation of MRSA in a free-living wild animal opens new perspectives in MRSA spread. Surveillance on lineages and their prevalence should be implemented among wild animal population to clarify host specificity and to assess zoonotic potential of S. aureus.