J Antimicrob Chemother doi:10.1093/jac/dkt526 Staphylococcus aureus ST398 detected in pigs in Australia Mitchell D. Groves 1,2 , Matthew V. N. O’Sullivan 3,4 , Huub J. M. Brouwers 2 , Toni A. Chapman 2 , Sam Abraham 5 , Darren J. Trott 5 , Rafat Al Jassim 1 , Geoffrey W. Coombs 6,7 , Robert L. Skov 8 and David Jordan 9 * 1 School of Agriculture and Food Sciences, The University of Queensland, Gatton, Queensland, Australia; 2 New South Wales Department of Primary Industries, Menangle, New South Wales, Australia; 3 Centre for Infectious Diseases and Microbiology, Westmead Hospital, Sydney, New South Wales, Australia; 4 Marie Bashir Institute for Infectious Diseases and Biosecurity, University of Sydney, Sydney, New South Wales, Australia; 5 School of Animal and Veterinary Sciences, The University of Adelaide, Roseworthy, South Australia, Australia; 6 Australian Collaborating Centre for Enterococcus and Staphylococcus Species Typing and Research, Curtin University, Perth, Western Australia, Australia; 7 Department of Microbiology and Infectious Diseases, PathWest Laboratory Medicine—WA, Royal Perth Hospital, Perth, Western Australia, Australia; 8 Department of Microbiological Surveillance and Research, Statens Serum Institut, Copenhagen, Denmark; 9 New South Wales Department of Primary Industries, Wollongbar, New South Wales, Australia *Corresponding author. Tel: +61-(2)-66261240; Fax: +61-(2)-66281744; E-mail: david.jordan@dpi.nsw.gov.au Keywords: antimicrobial resistance, MRSA, swine Sir, Livestock-associated methicillin-resistant Staphylococcus aureus (MRSA) have recently emerged in many countries. They appear adapted for transmission amongst intensively managed animals, including pigs, cattle, poultry and horses. 1 Those belonging to multilocus sequence type (ST) 398 have notably caused serious infections in humans exposed to colonized animals. 1 To date, MRSA has not been reported in food-producing ani- mals in Australia. However, ST398 MRSA was recently detected in a nasal swab from a swine veterinarian in Australia. 2 A lack of targeted surveillance means that the presence of MRSA in Australian food-producing animals may have gone undetected. We report here the first detection of MRSA in Australian pigs, the molecular characteristics of the recovered isolates and the impact on our understanding of the global epidemiology of this priority pathogen. Nasal swabs were collected from 324 pigs in five commercial herds and one feral herd between January 2009 and October 2010. Swabs were obtained from herds in Western Australia (feral pigs, Herd 1), Queensland (Herd 2), Victoria (Herd 3) and New South Wales (Herds 4–6). The collection of nasal samples from pigs was approved by the Animal Ethics Committee of the Elizabeth Macarthur Agricultural Institute, Menangle, New South Wales (reference M10/06). Swabs were suspended in 2 mL of brain heart infusion broth (Oxoid, Adelaide, Australia) containing 20% (v/v) glycerol and stored at 2808C. Pools containing 100 mL each of five nasal samples were prepared in 2 mL of Mueller– Hinton broth (Oxoid) containing 6.5% NaCl and enriched overnight at 358C. Each pool was analysed by PCR for markers indicative of MRSA ( femB and mecA). 3 Individual samples constituting PCR-positive pools were retrospectively analysed for MRSA using selective enrichment and isolation procedures described else- where. 4 Two presumptively positive MRSA colonies were selected per sample. Isolates were confirmed as MRSA using femB/ mecA PCR. An ST398 MRSA isolate recovered from the nasal pas- sages of an Australian porcine veterinarian 2 was included in the molecular investigation. All isolates were typed by multilocus sequence typing (http://saureus.mlst.net/), spa typing (http:// spaserver.ridom.de), SCCmec typing, 5 dru typing 6 and binary typ- ing. 7 Isolates underwent susceptibility testing against 19 anti- microbials using a Phoenix TM automated system and against tetracycline by disc diffusion. CLSI performance and interpretive criteria were used. 8 MRSA was isolated from 0.9% (n ¼ 3) of 324 pigs. Six MRSA iso- lates were recovered; two each from 3 of 70 pigs from Herd 4. All isolates were characterized as ST398, harboured the type V SCCmec element, belonged to spa type t1184 or t11373, belonged to dru type dt11v or dt11ck, belonged to binary type 21072 and were resistant to all tested b-lactams, tetracycline, erythromycin, clindamycin and trimethoprim/sulfamethoxazole (Table 1). The veterinarian-associated ST398 MRSA isolate har- boured the type V SCCmec element, belonged to spa type t1451, belonged to dru type dt11a and belonged to binary type 30224 (Table 1). There was considerable similarity among the detected spa, dru and binary types. This study confirms that ST398 MRSA is established within pigs in Australia. Although it is possible that ST398 MRSA may have independently evolved in Australia, our findings suggest that iso- lates from this work have a common ancestry with European iso- lates. The extent of spatio-temporal movements of MRSA is supported by evidence of the hypervariability of the X-region of the staphylococcal protein A gene and the mec-associated dru region. 9,10 Two spa types found in this study (t1184 and t1451) were detected among ST398 MRSA in Europe 11 ≥2 years prior to the collection of samples for this work. Moreover, dru types dt11a and dt11v have been observed among contemporaneous ST398 MRSA in Europe. 12 The absence of ST398 MRSA in other MRSA research and surveillance activities in Australia 13 is consistent with the pathogen recently becoming established in Australian pigs following an exotic incursion. It is unlikely that imported pigs or poultry are the source of ST398 MRSA in the Australian pig herd due to the ban on the live importation of these animals 14 and the strength of quarantine measures. Human carriers are a likely mechanism since there are # The Author 2014. 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