Drug-Resistant Bacteria Found In Workers At Industrial Farms
The ongoing use of antibiotics in livestock has spawned controversy over the extent to which these medications jeopardize human health by causing resistance to develop to the drugs. Two months ago, for instance, a bill was introduced in the US Senate to limit antibiotic use in livestock. And for the second time this year, a study published in PLOS One indicates that such concerns have merit.
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. The drug-resistant bacteria examined were Staphylococcus aureus, which is commonly known as Staph and includes MRSA, a bacterium that is responsible for several difficult-to-treat infections in humans.
Although all of the workers in the study had direct or indirect contact with livestock, only the industrial workers carried antibiotic-resistant Staph with multiple genetic characteristics linked to livestock. A total of 204 livestock workers and household members had their noses swabbed. Staph aureus were assessed for antibiotic susceptibility and the absence of the scn gene, which is a marker of livestock association.
They found 37 percent of 41 industrial livestock workers and household members tested positive for multi-drug resistant Staph aureus compared with 19 percent of 42 antibiotic-free livestock workers and their household members. Similarly, 46 percent of the industrial livestock participants tested positive for tetracycline resistant Staph aureus, compared with 2.4 percent of the antibiotic-free participants. And 31.7 percent of industrial livestock participantes tested positive for CC 398, which is the type of Staph aureas most associated with livestock, compared with 2.4 percent of antibiotic-free participants (here is the study; see Table 3 for more findings).
“The presence of carriage was higher in industrial livestock workers,” Chris Heaney, an assistant professor of environment health sciences and epidemiology at the Johns Hopkins Bloomberg School of Public Health and a study co-author, tells us. “We saw drug-resistance strains of Staph aureas with multiple genetic characteristics linked to livestock in only one group – industrial livestock workers.”
Concerns over antibiotic resistance reflect growing use of antibiotics by livestock operators in feed and water to promote animal growth, as opposed for therapeutic uses. Previous studies have detected strains of drug-resistant Staph aureus from livestock among farm workers and in hospital and community settings in Europe.
In the US, strains have been detected among industrial livestock workers in Iowa, another major livestock producer that exceeds only North Carolina in hog production. Another study, which was published in PLOS One last May, and swabbed pigs and farm workers at 45 swine herds in Illinois, Iowa, Minnesota, North Carolina and Ohio reached a similar conclusion (see this).
Consumer advocates argue antibiotic livestock use is contributing to a public health crisis and contend the FDA should increase its oversight. The groups also maintain the FDA needs additional authority from Congress in order to better monitor antibiotic usage and collect applicable data. The ‘Preventing Antibiotic Resistance Act’ would require drugmakers and agricultural producers to demonstrate that antibiotics are used to treat clinically diagnosable disease and not just fatten farm animals (back story with a link to the bill).
The latest results are being flagged by advocates as further proof that the legislation needs to be passed. “What was different about the results were the farmers in the conventional working group had a type of staph that was resistant to bacteria and it suggested it really came from the animals and wasn’t being passed back and forth among other people,” says Gail Hansen, a senior officer in the campaign on human health and industrial farming at Pew Charitable Trusts.
“We’ve been hearing from industry that there’s no proof that antibiotics given to food-producing animals poses a threat to public health or contributes to antibiotic resistance in human disease,” she continues. “This study would seem to show that is a false premise.”
We asked the National Pork Board for comment and will update you accordingly.
[UPDATE: A spokeswoman for the National Pork Board sent us this: "This study has several scientific flaws. If you look carefully at the data, the authors’ conclusions were based on a sample size of only three people, the animal populations (poultry and swine) were not identified or sampled, and the authors’ objective to establish a link between antibiotic use in food animals and MRSA was not scientifically proven. While swine workers may experience a greater level of exposure to livestock-associated MRSA than the general community, this does not mean they will get disease.
"Reports of related disease in healthy livestock workers are few. (in fact, in the US there has not been a single case of clinical disease due to the Livestock Associated strain of MRSA reported to the CDC)Studies in Europe have shown that exposure risk appears to be limited to people having direct contact with pigs and did not extend to people in the adjacent communities.
"The antimicrobial resistances reported in this study have little, if anything, to do with antibiotic usage. As an example, tetracycline resistance has been found in MRSA from farms not using any tetracycline products. In addition, the resistances reported in the study also have little, if any, potential impact on the ability to treat clinical disease if it were to occur. Tetracycline would not be used to treat MRSA infections in humans.
"Staphylococcus aureus is a common bacterium found on the skin of people (30% of the population) and animals. It would have been unusual for the study’s authors NOT to have found it in their samples. While Staph can cause illness in people, it usually does not. It most affects people with compromised immune systems, open wounds or invasive devices – thus the reason that the vast majority of Staph infections occur in health-care facilities."]
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