Molecular Bacteriology.com

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       Staphylococcus aureus is part of the normal human bacterial flora, and is found primarily in the nares.¹ Approximately 20% of humans are persistently colonized.^2,3 S. aureus causes serious invasive infections including endocarditis, osteomyelitis, bacteremia, pneumonia, necrotizing fasciitis, and toxic shock syndrome. This organism is of great concern in hospitals, because of its common occurrence and its increasing antimicrobial resistance—in particular, the increasing frequency of methicillin-resistant S. aureus (MRSA). MRSA is often labeled a “super-bug” by the media because of the scarcity of antibiotics to which it is susceptible, and it is one of the foremost clinical problems related to antimicrobial resistance. Although historically this problem has been largely confined to health care institutions (i.e., it is primarily a ‘hospital acquired’ infection), in recent years ‘community-acquired’ strains of MRSA have also become a significant problem in many countries, often in young, healthy patients. MRSA has also been reported in cats,⁴ dogs,^{5, 6} horses,⁶ pigs,⁷ and chickens,⁸ and we now have evidence of interspecies transmission. Thus, it is important to look not only at humans as sources of MRSA, but also possible animal and animal product reservoirs.

       Pork is reported to have a high prevalence of MRSA in some countries. An extensive review published in June 2007 by the UK Soil Association (an organic farming group) includes a letter from a Dutch government official stating that MRSA was identified in 20% of pork samples (20 of 25), as well as in chicken and beef samples.⁹ The same report cites studies finding MRSA in meat in Jordan (1% of samples of beef and sheep; 2% of chicken samples), and Korea (1% of samples of retail chicken meat). A recently published study from the Netherlands has found a prevalence of 2.5% in raw pork products¹⁰ and similar study is being conducted in Canada. Given that foodborne outbreaks of MRSA have been previously documented,¹¹ these observations have sparked discussion in the media about the possible foodborne transmission of MRSA,¹² particularly in pork. To address this issue of the MRSA “superbug” objectively, we must collect the pertinent data on the existence and extent of MRSA colonization of pork in the USA. This pork surveillance is part of a three-part study on MRSA in pigs, pork, and swine veterinarians in the USA conducted by the University of Minnesota funded by the National Pork Board.