Livestock-associated methicillin-resistant Staphylococcus aureus in slaughtered pigs in England

This study was performed to investigate the occurrence of livestock-associated methicillin-resistant Staphylococcus aureus (LA-MRSA) in batches of pigs at slaughter and at different stages along the slaughter line. Nasal and ear skin swabs were collected from 105 batches of 10 pigs at six abattoirs. Cultures (pooled or individual) were performed for MRSA using selective media; presumptive MRSA were confirmed by mecA and nuc gene detection and a selection was spa-typed. MRSA was detected in 46 batches. All spa-types detected were those associated with LA-MRSA clonal complex 398. The proportion of positive batches varied among abattoirs (0–100%). Two abattoirs were subsequently further investigated, with samples taken at post-stunning, chiller and either at lairage or post-singe. Results suggested cross-contamination occurred between the lairage and point of post-stunning, but the slaughter processes appeared effective at reducing contamination before carcases entered the chiller. One abattoir provided only negative samples in the initial study and in the subsequent study along the slaughter line (26 batches in total), suggesting differences possibly in the MRSA status of pigs on arrival from supply farms or in its abattoir practices affecting the MRSA status of pigs at the sampling points. This study highlights that in the investigated abattoirs, MRSA was detected in 43.8% of batches of pigs at slaughter using sensitive selective culture methods.