P1-50 Prevalence and Characterization of Methicillin-resistant Staphylococcus aureus Isolated from Commercial Pork Processing Plants in Canada

Monday, July 29, 2013
Exhibit Hall (Charlotte Convention Center)
Toufeer Mehdi, Agriculture and Agri-Food Canada, Lacombe, Canada
Claudia Narvaez Bravo, University of Manitoba, Winnipeg, Canada
Scott Weese, University of Guelph, Guelph, Canada
Moussa Diarra, Agriculture and Agri-Food Canada, Agassiz, Canada
Deckert Anne, Public Health Agency of Canada, Guelph, Canada
Richard Reid-Smith, Public Health Agency of Canada, Guelph, Canada
Mueen Aslam, Agriculture and Agri-Food Canada, Lacombe, Canada
Introduction: Among livestock, pigs represent the highest prevalence of methicillin-resistant Staphylococcus aureus (MRSA) colonization, with health consequences in pig farmers/workers and potential for broader community-associated MRSA infections in humans. While epidemiology of MRSA in pigs on farms has been extensively studied, little information is available about the sources of contamination and prevalence of MRSA in slaughter plants.

Purpose: The aim of this study was to determine the MRSA prevalence at several points during the swine slaughter process and in retail pork from these slaughter plants.  

Methods: Three plants (A, B and C) were selected in Alberta, Canada and approximately 220 samples were collected from four points during slaughter and processing in each plant for a total of 2,640 samples. Samples sources were: nasal swabs after bleeding (NSAB), nasal swabs after scalding (plant B) or skinning (plant A, C) (NSAS/S), carcass swabs after pasteurization (plant B) or washing (plant A, C; CSAP/W) and retail pork products (RP). MRSA was isolated and confirmed using standard cultural and molecular methods. Randomly selected MRSA isolates were spa typed (539 isolates) and antimicrobial susceptibility (246 isolates) was tested for 21 antimicrobials.  

Results: Overall MRSA prevalence was 37.5% (330/880), 12.7% (112/880) and 24.2% (213/880) in plant A, B and C, respectively. NSAB samples showed the highest MRSA prevalence (plant A: 77.3%, 170/220; plant B: 34.7%, 77/220 and plant C: 74.1%, 163/220), followed by NSAS/S samples (plant A: 48.9%, 107/219; plant B: 14.1%, 31/220 and plant C: 22.3%, 49/220). The MRSA prevalence in CSAP/W samples was 20.9%, 1.8% and 0% in plant A, B and C, respectively. There was no MRSA detected in RP from plant B, whereas MRSA prevalence was about 3.2% (7/220) and 0.5% (1/220) in plants A and C, respectively. The majority (400/539) of MRSA isolates from the three plants belonged to the livestock-associated MRSA spa type t034 (ST398; 74.2%) followed by t002 (15%), and t011 (3.8%). The spa types t2971, t4030, t6408, t067, t1184, t808 and t777 were also found in < 1% of isolates. Furthermore, in addition to β-lactams (> 98%), MRSA isolates were often resistant to tetracycline (97%) with low rates of resistance to erythromycin (0.8%), clindamycin (0.8), gentamicin (0.8%), levofloxacin (0.5%), quinupristin/dalfopristin (1.6%).

Significance: This study suggests a reduction in the MRSA prevalence through the slaughter process. The predominant spa-type was t034 (ST398) followed by t002 and t011. It appears that standard intervention strategies applied in the pork plants help to reduce MRSA contamination of retail pork.