A new, potentially deadly strain of MRSA superbug has been found in British milk for the first time, revealing that the bacteria are spreading through the UK livestock population.

The new strain of MRSA (Methicillin-resistant Staphylococcus aureus), known as ST398, is resistant to antibiotics and can cause serious and even deadly infections in humans.

The superbug, which has become an increasingly frequent cause of udder infections in dairy cows, was discovered from tests on 1,500 samples. Researchers found seven cases of RSA ST398 from five farms in England, Scotland and Wales.

Cambridge University scientists who first identified MRSA in milk in 2011, say that the latest discovery of a different strain is troubling, adding that it shows that the superbug is gaining an increasing hold in the dairy industry.

In theory, bacteria germs are destroyed in the pasteurization process, when the milk is heat-treated before it is bottled and delivered to groceries for consumer use. According to experts, there is no risk of MRSA infection to consumers of dairy products as long as the milk is pasteurized.

However, the problem comes from farmers, vets and abattoir workers who may become infected through contact with cows and could transmit the bug to others. This has happened in the Netherlands where the same strain of MRSA has caused an outbreak among residents in a nursing home.

MRSA ST398 was first detected in pigs in the Netherlands in 2003. Since then, it has become widespread in European and North American pig populations and has spread to poultry and cattle.

The latest news comes amid growing concern over the use of antibiotics on farms.

MRSA ST398 is one of a number of superbugs that have emerged in recent years, apparently because of the overuse of antibiotics by farmers treating sick animals, and over time, the farm animal bacteria develop resistance to antibiotics. Experts say the more antibiotics are used, the greater the risk the bacteria will develop resistance, and superbugs such as MRSA will evolve.

Mark Holmes, of the department of veterinary medicine, who led the new study, published in Eurosurveillance, said that the latest findings show "definitely a worsening situation," according to The Independent.

"In 2011 when we first found MRSA in farm animals, the Department of Environment, Food and Rural Affairs [Defra] initially didn't believe it. They said we don't have MRSA in the dairy industry in this country," Holmes told the UK newspaper. "Now we definitely have MRSA in livestock. What is curious is that it has turned up in dairy cows when in other countries on the Continent it is principally in pigs. Could it be in pigs or poultry in this country? We don't know."

Researchers believe that as the bacteria becomes more common, it will soon or later cause disease in people.

In fact, according to the UL Department for Environment, Food and Rural Affairs, human cases of the infection with the new strain have already been detected in Scotland and northern England.

Homes said that the supermarket pressure on famers for low prices was the leading cause for the overuse of antibiotics, which prevent cattle from getting mastitis, an udder infection that could interrupt the milk supply.

"If farmers were not screwed into the ground by the supermarkets and allowed to get a fair price for their milk they would be able to use fewer antibiotics," he said, according to The Independent. "Common sense tells us that anything we can do to reduce use of antibiotics will reduce the growth of resistant bugs. We want to wean our farmers off antibiotics and the only way we can do that is with better regulation."