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Unexpectedly high levels of MRSA found in retail pork products
O’Brien AM. PLoS One. 2012;7:e30092.
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Results of a new study confirm the presence of Staphylococcus aureus on raw pork products in the United States at higher levels reported in previous studies from the Netherlands.
The recent study from Iowa found no difference between conventionally produced swine or those raised without antibiotics and/or antibiotic growth promotants, referred to as alternative pork products. Researchers at the University of Iowa and the Institute for Agriculture and Trade Policy also found no statistically significant differences when they compared S. aureus (methicillin-sensitive S. aureus and methicillin-resistant S. aureus) positivity on conventional and alternative pork products.
It is possible that a link between antibiotic use on the farm and MRSA on meat products may be obscured by human contamination of meat with MRSA after slaughter, according to investigators.
“Human carriage of MRSA in the US is approximately 50 times higher than what has been reported in the Netherlands (1.5% vs. 0.03%),” the researchers said.
The researchers collected 395 pork samples from 36 stores in Iowa, Minnesota and New Jersey, from which S. aureus was isolated from 256 samples (64.8%; 95% CI, 59.9-69.5). The bacteria were isolated from 67.3% (202/300) of conventional pork samples and from 56.8% (54/95) of alternative pork samples. MSSA was present on 230 samples (58.2%; 95% CI, 53.2-63.1); 61% (183/300) of conventional samples and 49.5% of (47/95) alternative samples.
MRSA was present on 26 pork samples (6.6%; 95% CI, 4.3-9.5), and no statistically significant differences were observed for the prevalence of S. aureus, in general, or MSSA or MRSA specifically.
These findings, according to investigators, are in contrast to findings from the Netherlands, where a lower prevalence of MRSA in meat from biological-reared chickens (raised using no growth promotants) and wild fowl and game was found, in comparison to the prevalence of MRSA found in conventionally raised poultry in the same study. The researchers of that study said their findings suggested a link between antibiotic use and prevalence of MRSA on meat products in Europe.
Similar results came from a study of US pigs that reported MRSA was found in four of nine conventional pig farms, but was absent from pigs raised without antibiotics.
Disclosure: This study was funded, in part, with support from the Claneil Foundation. No additional external funding was received for this study. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
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We know that the first little piggy went to market; however, we didn't realize he brought Staph with him. In this study by O'Brien and colleagues, commercial pork samples were assessed for both MSSA and MRSA. Staphylococci were frequently recovered from these raw samples, and there were no differences observed between MRSA frequencies in animals that were labeled "antibiotic free" vs. conventional pork.
This is a clear reminder to us and to our patients that the food we eat is by no means sterile and that staphylococci are important causes of foodborne infections. Not only are these organisms a leading cause of hyperacute gastroenteritis (via preformed enterotoxin), but the food we consume is also an important source of colonizing microbes.
C. Buddy Creech, MD, MPH
Infectious Diseases in Children Editorial Board