In a new study from the United States, released earlier this week, researchers found drug-resistant bacteria associated with livestock in the noses of industrial livestock workers in North Carolina, but not in the noses of antibiotic-free livestock workers.

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The drug-resistant bacteria examined were Staphylococcus aureus, commonly known as "Staph," which include the well-known 'superbug' MRSA. The researchers, from the University of North Carolina and Johns Hopkins Bloomberg School of Public Health, working in conjunction with scientists from other institutes, said they conducted their study to investigate the emergence of new Staph strains in people who have close contact with livestock animals.

They found that, while everyone in the study had direct or indirect contact with livestock, only industrial workers carried antibiotic-resistant, 'livestock-associated' Staph. Earlier studies in Iowa, another major livestock state, and the Netherlands yielded similar results. The US team said the weight of evidence "raises concern about antibiotics use in livestock production," particularly sub-theraputic doses to improve growth. Although this practice is outlawed in Europe, campaigners have raised concerns over other routine uses of antibiotics.

The North Carolina researchers said earlier studies from Europe suggested resistant bacteria first detected amongst farm workers had then spread out into the wider population, adding that they were "concerned that these bacteria could follow a similar trajectory into the community".

S. aureus can cause a range of illnesses in humans, from minor to life-threatening skin, bloodstream, respiratory, urinary and surgical site infections. Like most illnesses caused by bacteria, S. aureus infections are treated with antibiotics. However, according to the US Centers for Disease Control and Prevention, resistance to antibiotics in Staph strains is growing, and some strains are resistant to multiple drugs.

The study was based on interviews and nose swabs that were collected and analysed from individuals who worked at two different types of livestock operations in North Carolina.  Researchers tested the S. aureus isolated from nose swabs for resistance to a range of antibiotics and for genetic markers which would suggest the bacteria had come from livestock.

Workers in anti-biotic free, more extensive systems were generally free of the resistant strains. Those working in 'intensive systems' were more than twice as likely to be carrying multi-drug resistant bacteria. Staf resistant to tetracycline – an antibiotic that has been used in livestock production in the US since the 1950s – were 19 times as prevalent among intensive workers, compared to those on antibiotic-free farms.

Christopher Heaney, Environmental Health Professor at Johns Hopkins Bloomberg School of Public Health, underlined the findings, "This study shows that these livestock-associated strains are present among workers at industrial livestock operations and that these strains are resistant not just to methicillin, but to multiple antibiotics – including antibiotics that are used to treat human infections."

The issue of antibiotic resistance was discussed by leaders of the 'Group of 8' richest nations, during their summit in Northern Ireland last month. In January, Conservative backbencher Zac Goldsmith raised the issue in Parliament. Goldsmith highlighted the role of antibiotics in agriculture and the potential health risks this poses, in addition to misuse in human treatment.

He called on the government to introduce better monitoring measures (including publishing surveillance data by antibiotic family and animal species, as has been pioneered in France), limit the use of critically important antibiotics (including implementing a ban on fluoroquinolones) and Improve animal health and welfare by limiting overcrowding "and the worst excesses of factory farming", to avoid the prophylactic use of antibiotics.

Mr Goldsmith said, "Factory farming interests have wielded enormous influence on government policy for many years." He suggested that any progressive moves on antibiotic use in agriculture will be "fiercely resisted by them." However, the Richmond MP warned, "If we continue to ignore the risks for fear of upsetting vested interests, we will be complicit in robbing future generations of one of the greatest discoveries of our species."