New MRSA Staph Strain Found In UK Cows; Pasteurized Milk Is Safe

By Sy Kraft

Medical News Today

6/3/11

Original article

A new variant of meticilin-resistant Staphylococcus aureus found in cow’s milk is genetically different to existing MRSA strains from the United Kingdom (UK). The original scare had Europeans not drinking milk, but a released study mentions that cows may simply be hosts to this new strand and normal processes of milk, such as pasteurization, will kill any risk to humans.

The study’s authors state:

“Such evidence suggests that a bovine reservoir exists, from which mecALGA251 MRSA is transmitted to people. Pasteurization of milk will prevent any risk of infection via the food chain but individuals in close contact with cattle could be at higher risk of carriage. Further research is needed to test this hypothesis. The discovery of this previously undetected mecA homologue is potentially of public health importance. Diagnostic protocols, whether for clinical or epidemiological purposes, should consider the ramifications of not detecting S aureus strains that carry this new mecA homologue.”

The resistance found in variants of MRSA is usually conferred by the mecA gene, which can be transferred between S. aureus strains. In today’s era of genetic testing, a positive test for the mecA gene has become the gold standard for identifying an MRSA. But in this new study, it was found an MRSA with a new mecA gene (a mecA homologue) that was not detected by the usual confirmatory test for mecA.

The study also shows indirect, although not conclusive, evidence that cows could be an important reservoir, or host, of this new-variant of MRSA infection in humans.

This new variant is associated with clinical disease in people, yet some existing testing methods would wrongly identify this new variant as meticillin-susceptible, leading to prescriptions of the wrong antibiotics.

MRSA is, by definition, any strain of Staphylococcus aureus that has developed resistance to beta-lactam antibiotics which include the penicillins (methicillin, dicloxacillin, nafcillin, oxacillin, etc.) and the cephalosporins.

MRSA is especially troublesome in hospitals and nursing homes where patients with open wounds, invasive devices and weakened immune systems are at greater risk of infection than the general public.

In terms of antibiotic resistance in hospitals, the UK has one of the worst records, particularly for MRSA. For people who are concerned about the possibility of MRSA infection in UK hospitals this has been one of the factors which have encouraged them to seek hospital treatment abroad.

The EARSS (European Antimicrobial Resistance Surveillance System) monitors antimicrobial resistance in Europe. It maintains a comprehensive surveillance and information system that provides comparable and validated data on the prevalence and spread of major invasive bacteria such as MRSA. According to EARSS (European Antimicrobial Resistance Surveillance System) Norway had less than 0.6% MRSA in 2005.

The increase in MRSA infection in UK hospitals is a growing concern for both doctors and patients. The number of cases of MRSA has been rising sharply – from 2,422 in 1997 in England and Wales, to 7,684 in 2003/4 in England alone. Official figures show that about 15% of reported MRSA cases result in death.