U.S. Study Identifies Livestock-Associated MRSA in Retail Pork

U.S. researchers have reportedly discovered methicillin-resistant Staphylococcus aureus (MRSA) in retail pork samples “at a higher rate than previously identified,” raising questions about the organism’s “overall ecology and transmission” in the food supply. Ashley O’Brien, et al., “MRSA in Conventional and Alternative Retail Pork Products,” PLoS One, January 2012. Conducted by the Institute for Agriculture and Trade Policy (IATP) and the University of Iowa College of Public Health, the study examined 395 fresh pork cuts collected from 36 stores in Iowa, Minnesota and New Jersey, in addition to comparing products “from conventionally-raised swine and swine raised without antibiotics.”

According to the analysis, researchers isolated S. aureus in 256 pork samples
(64.8 percent) and MRSA in 26 samples (6.6 percent) but discovered “no
significant difference” in prevalence between conventional and alternative
pork products. The study notes, however, that 26.9 percent of MRSA isolates
were a “livestock-associated” strain known as ST398 (t034, t011) as opposed
to human types t002 and t008, which have also been found in live swine. To
this end, the authors urge further investigation of potential cross-species
transmission, citing Canadian and Dutch studies as well as research covered in
Issue 391 of this Update that reported S. aureus in 47 percent of 136 meat and
poultry samples.

“The latest results are more than double the prevalence found in previous studies of this kind,” said IATP Senior Advisor in Science, Food and Health David Wallinga in a January 20, 2012, press release. “At 6.6 percent, pork is four times more likely to be carrying deadly MRSA than the average American, pointing to our food system and industrial farming as an avenue for MRSA to continue to spread.”