Clostridium difficile and methicillin-resistant Staphylococcus aureus shedding by slaughter-age pigs

BACKGROUND: Clostridium difficile and methicillin-resistant Staphylococcus aureus are critical human pathogens and of increasing concern in food animals. Because of the apparent impact of age on prevalence of these organisms, studies of slaughter age pigs are important when considering the potential for contamination of food. This study evaluated C. difficile and MRSA shedding by slaughter age pigs from farms across Canada. RESULTS: Clostridium difficile was isolated from 30/436 (6.9%) samples from 15/45 (33%) farms. After adjusting for clustering at the herd level, the prevalence was 3.4%. Ribotype 078 (toxinotype V, North American Pulsotype 7) was the most common strain, accounting for 67% of isolates. MRSA was isolated from 21/460 (4.6%) pigs from 5/46 (11%) farms. The prevalence in pigs after adjusting for clustering at the herd level was 0.2%. Seven different spa types were identified, with 3 related spa types (t011, t034, new) accounting for 16 (76%) consistent with ST398 predominating. Both MRSA and C. difficile samples were collected from 45 farms. Both MRSA and C. difficile were detected on 2 (4.4%), with C. difficile only on 13 (29%), MRSA only on 3 (6.7%) and neither on 27 (60%). CONCLUSIONS: The prevalence of C. difficile and MRSA in slaughter age pigs was relatively low, particularly in comparison with studies involving younger pigs. The predominance of C. difficile ribotype 078 and MRSA ST398 was not surprising, but there was diversity in strain types and the majority of isolates of both organisms were strains that can be found in humans. While the prevalence of C. difficile and MRSA in slaughter age pigs was relatively low, there is clearly potential for contamination of meat from healthy pigs carrying this pathogen into slaughterhouses.