Methicillin-resistant Staphylococcus aureus isolated from retail meat in the Canadian maritime provinces

Food animals and their products have been suggested to be an important source of antimicrobial resistant organisms, including methicillin-resistant Staphylococcus aureus (MRSA). While MRSA has been detected in livestock and meat products in various regions of Canada and the world, there are no estimates of MRSA in livestock or retail meat in Atlantic Canada. Overall, this region has lower estimates of methicillin-resistant staphylococci in animals. The objective of this study was to determine the prevalence and molecular types of MRSA in beef, pork and poultry in raw retail samples collected in New Brunswick, Nova Scotia and Prince Edward Island. It was hypothesized that the prevalence of MRSA in retail meats in the Canadian Maritimes would be lower than reported in other Canadian regions. Samples and epidemiologic data were collected as part of the Canadian Integrated Program for Antimicrobial Resistance Surveillance, which focusses on antimicrobial resistance among enteric bacteria. Isolation was completed by enrichment in broth containing mannitol and sodium chloride, followed by culturing to chromogenic agar. Isolates were tested for coagulase production, mannitol fermentation and resistance to oxacillin and cefoxitin. Detection of penicillin-binding protein 2a (PBP2') by latex agglutination was used to confirm methicillin-resistance. A multiplex PCR assay was used to differentiate between coagulase-positive staphylococci of veterinary significance: S. aureus, the S. intermedius group, and S. hyicus. Strain types were determined by sequence analysis of the X region of protein A (spa typing). Culture results from 195 samples (56 of each chicken, beef and pork, and 27 turkey) have been completed to date. The overall prevalence of MRSA in raw retail meat was 2.1% (4/195), while the prevalence in chicken was 5.4% (3/56), in beef 1.8% (1/56) and in pork and turkey 0%. All isolates displayed typical phenotypic characteristics of MRSA, and were PBP2' positive. Molecular typing is being completed and will be presented. These results are in contrast with a Canadian study where MRSA was primarily isolated from pork, with samples of chicken being the least likely to be MRSA positive. Determination of the strain type will provide insight to whether the MRSA isolated is human or livestock associated, and will lend evidence to the source of the contamination. Factors associated with MRSA contamination of retail meat will be explored.