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Do People Catch Antibiotic Resistance From Cattle?

Livestock are often blamed for a lot of the antimicrobial resistant pathogens encountered in human medicine. But if antimicrobial use in cattle really contributed to antimicrobial resistance in human pathogens, wouldn’t the feedlot staff who use veterinary antimicrobials to treat sick cattle be the first people to develop antimicrobial resistance? Fortunately, those questions have already been answered by a Canada-Alberta Beef Industry Development Fund study led by Dr. Ron Read of the University of Calgary’s Department of Medicine.

What they did:In four southern Alberta feedlots, nasal and rectal swabs were collected from 2,662 cattle on arrival, after 70 days on feed, and prior to feedlot exit. These samples were examined for antimicrobial resistance in a variety of microbes. Employees who worked closely with cattle at those same feedlots provided their own nasal and rectal swabs at the beginning and end of the cattle-feeding period. Samples from these 61 staff were also examined for evidence of antimicrobial resistance in a variety of microbes. Antimicrobial resistance results from these staff were compared with historical information from the Calgary Health Region. Some of the pathogens they looked for included:

Methicillin-resistantStaphylococcusaureus (MRSA):MRSA is found in the noses of one to three per cent of healthy Canadians. It generally doesn’t cause problems unless people are under-nourished or have a poor immune system. But MRSA is resistant to all antibiotics in the penicillin family, as well as many others. This means that although MRSA infections are rare, they are extremely difficult to treat. MRSA has also been isolated from retail meat samples in Canada.

Vancomycin-resistant Enterococcus (VRE):Enterococci are normally found in the human digestive tract, urinary tract and the environment, and rarely cause problems in healthy people. In contrast, VRE is resistant to vancomycin, a drug of Very High Importance in human medicine. VRE causes a variety of symptoms, and is sometimes found in hospitalized people with weak immune systems or who have been treated with antibiotics for extended periods of time.

Salmonellais not ordinarily found in people or cattle. Among other things, it can cause intestinal cramps, vomiting and diarrhea; cattle can develop intestinal problems as well. In other studies, a rare strain ofsalmonellathat is simultaneously resistant to 10 different classes of antimicrobials has been isolated from both sick cattle and people.

Campylobacteris believed to be one of the most common causes of gastrointestinal illness in humans worldwide. It does not cause gastrointestinal disease in cattle. As usual, people who are already in poor health are the most susceptible. Contaminated water, shellfish, livestock and pets can all serve as sources of infection.

E.coliisfound in the digestive tract of every warmblooded animal and human on the planet. There are many, many strains ofE. coli.The vast majority are harmless, but a minority ofE. colistrains can cause extreme gastrointestinal problems and worse.

Ampicillin-resistantE. coli:ampicillin is a drug of High Importance in human medicine.

Gentamicin-resistantE. coli:gentamicin is a drug of High Importance in human medicine.

Ciprofloxacin-resistantE. coli:ciprofloxacin is a drug of Very High Importance (drug of last resort) in human medicine.

What they learned: No MRSA was found in the cattle or the feedlot staff. No VRE was found in the cattle or the feedlot staff. Nosalmonellawas found in the cattle or the staff. Campylobacterwas found in the cattle, but was not in the feedlot staff.

Ampicillin-resistantE. coliwas more common in feedlot staff than in cattle at the start of the feeding period. Ampicillin-resistantE. coliin feedlot staff declined over the feeding period, and was considerably lower than in the records maintained by Calgary Lab Services. Gentamicin-resistantE. coliwas slightly more common in feedlot staff than in cattle at the start of the feeding period, and became less common in feedlot staff as the feeding period progressed. It was found at similar levels in Calgary Lab Services records. Ciprofloxacin-resistantE. coliwas not found in the feedlot cattle at arrival or exit, or the feedlot staff. But it was found at a low level in records of Calgary Lab Services.

What it means:Although feedlot staff use veterinary antimicrobials to treat sick cattle, the prevalence of antimicrobial- resistant bacteria was no higher in feedlot staff than in the population represented in Calgary Laboratory Services records. This study has not been formally published, because it is notoriously difficult to prove that a finding of “no difference” is scientifically valid. Research of this sort helps to demonstrate that responsible use of veterinary products benefits animal health and welfare without negatively impacting human health. Producers enrolled on the Canadian Cattlemen’s Association’s Verifi ed Beef Production program follow industry-sanctioned practices that demonstrate that they select, use, store and dispose of antimicrobials in a responsible manner. For more information on Verified Beef Production, go to www.verifiedbeef.org or call 306-737-2290.

ReynoldBergenisthesciencedirectorfortheBeefCattle ResearchCouncil.AportionoftheNationalcheckoffis directedtotheBCRCtofundresearchanddevelopment activitiestoimprovethecompetitivenessandsustainabilityof Canada’sbeefindustry.

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Dr. Reynold Bergen is the science director of the Beef Cattle Research Council.

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