Scientists discover new strain of superbug in milk of British cows

A NEW strain of the MRSA superbug has been found in the milk of British cows as well as swab samples taken from humans.

Experts have ruled out any general threat to the safety of milk or dairy products.

But they point to "circumstantial" evidence of the bacteria passing between cattle and humans.

Researchers discovered the new MRSA bug while investigating mastitis, a serious and potentially lethal disease which affects dairy cows. Using an upgraded test, scientists subsequently found MRSA bacteria with the same mutated gene in 13 of 940 samples from 450 dairy herds in England.

Further research confirmed that the strain was in the human population. Samples taken from screening tests and people treated for MRSA revealed 12 instances of the strain from Scotland, 15 from England and 24 from Denmark. Later the strain was also identified in Ireland and Germany.

MRSA, or Methicillin-resistant Staphylococcus aureus, is a drug-resistant form of a usually harmless common bacterium which can be deadly when it infects wounds.

Researcher Dr Laura Garcia-Alvarez, from Cambridge University, said it was "certainly worrying" to find the same new strain in both cows and humans. But she pointed out that the pasteurisation of milk, which destroys S. aureus, would keep the bacteria out of the food chain.

Unpasteurised dairy products, including cheese, are not thought to be a serious concern. They can only be sold directly from farms in England, and are banned from sale altogether in Scotland. The bugs also find it difficult to thrive in an acid "cheesey" environment.

The discovery has fuelled controversy over intensive farming methods and the way antibiotics are used to protect livestock.

The Soil Association called for a complete ban on routine use of the drugs, which are said to promote the development of drug-resistant bacteria.

It also urged an end to the continuing economic pressure on farmers to cut costs and maintain low prices.

Helen Browning, director of the Soil Association, said: "In the relentless drive for increased per animal productivity, and under acute price pressure, dairy systems are becoming ever more antibiotic dependent. We need to get farmers off this treadmill, even if that means that milk has to cost a few pennies more.

"That would be a very small price to pay for maintaining the efficacy of these life-saving drugs."

Dr Mark Holmes, the Cambridge University veterinary scientist who led the research, spoke of the "tremendous financial pressure" placed on farmers by the purchasing power of big supermarkets. The research is published today in the journal The Lancet Infectious Diseases.

The bug, often found in hospitals, was linked to 1,593 deaths in 2007, but since then the number of suspected fatal cases has fallen dramatically. There were 1,290 deaths in 2008 and 781 in 2009.