The presence of methicillin-resistant Staphylococcus aureus (MRSA), multidrug-resistance (MDR), and the subtype ST398 in the meat production chain and the genetic similarity between strains of porcine origin (meat and animals) suggest the possible contamination of meat during slaughtering and its potential transmission to humans.

That is the conclusion drawn by researchers led by Esra Buyukcangaz from Uludag University in Turkey and co-authors from the US and Chile of a paper in the journal, Foodborne Pathogens and Disease.

The objective of their study was to determine the prevalence and molecular typing of methicillin-susceptible S. aureus (MSSA) and MRSA in food-producing animals and retail meat in Fargo, North Dakota.

A two-step enrichment followed by culture methods were used to isolate S. aureus from 167 nasal swabs from animals, 145 samples of retail raw meat and 46 samples of deli meat.

Positive isolates were subjected to multiplex polymerase chain reaction in order to identify the genes 16S rRNA, mecA and Panton-Valentine Leukocidin. Pulsed-field gel electrophoresis and multilocus sequence typing were used for molecular typing of S. aureus strains.

Antimicrobial susceptibility testing was carried out using the broth microdilution method.

The overall prevalence of S. aureus was 37.2 per cent (n=133), with 34.7 per cent (n=58) of the animals positive for the organism, and the highest prevalence observed in pigs (50.0 per cent) and sheep (40.6 per cent; p<0.05); 47.6 per cent (n=69) of raw meat samples were positive, with the highest prevalence in chicken (67.6 per cent) and pork (49.3 per cent; p<0.05) and 13.0 per cent (n=6) of deli meat was positive.

Five pork samples (7.0 per cent) were positive for MRSA, of which three were ST398 and two were ST5. All exhibited penicillin resistance and four were multidrug-resistant (MDR).

The Panton-Valentine Leukocidin gene was not detected in any sample by multiplex polymerase chain reaction. The most common clones in sheep were ST398 and ST133, in pigs and pork both ST398 and ST9, and in chicken ST5. Most susceptible S. aureus strains were ST5 isolated from chicken.

The MDR isolates were found in pigs, pork and sheep.

Reference

^{Buyukcangaz E., V. Velasco, J.S. Sherwood, R.M. Stepan, R.J. Koslofsky and C.M. Logue. 2013. Molecular typing of Staphylococcus aureus and Methicillin-resistant S. aureus (MRSA) isolated from animals and retail meat in North Dakota, United States. Foodborne Pathogens and Disease. 10(7):608-617. doi:10.1089/fpd.2012.1427}