Livestock-associated strains of methicillin-resistant Staphylococcus aureus (MRSA) have been isolated from samples of pork on retail sale in the UK by two recent studies, prompting concern over the spread of antibiotic-resistant bacteria in the human food chain.
The first study, commissioned and reported by the Guardian newspaper, tested 100 packs of pork chops, bacon and gammon sold in supermarkets. Of these, 74 originated in Denmark, 25 in the UK and one in Ireland. A single strain of livestock-associated MRSA (CC398) was isolated from nine of the samples – eight Danish and one Irish.
The second study, carried out by scientists at Cambridge University, was commissioned by the campaign group Alliance to Save our Antibiotics and tested 52 samples of British-produced pork purchased from supermarkets in England. One sample of sausage contained two different strains of livestock-associated MRSA, while a third strain was found in a sample of pork mince.
The MRSA CC398 strain isolated in the Guardian study is known to be endemic in pig production units in Denmark and some other countries, but has only been recorded twice in pigs from UK farms. It is therefore not surprising that it can be found in pork samples produced in Denmark. The strain is associated with animals and is distinct from strains causing MRSA infections in hospitals.
There is thought to be little chance of human infections caused by eating pork contaminated with livestock-associated MRSA and the Food Standards Agency has stated that the risk is, “very low when usual good hygiene and thorough cooking practices are observed.” The Agency has also pointed out that there is no clear evidence of any cases of human infection with LA-MRSA CC398 from eating meat, even in countries where the strain is common in pig production.
Nevertheless, concerns have been expressed about what the findings mean for the spread of resistance to clinically important antibiotics. Many experts believe that livestock-associated MRSA strains have developed because of the historical overuse of antibiotics in intensive farming and that the food chain is now a reservoir for resistance that could spread to other more dangerous pathogens.
Read the Guardian report here.