A lengthy Canadian study shows no major link between cattle production and antibiotic resistance in humans.
“Many significant resistance concerns that we were looking for when we started this project turned out not to be an issue,” said Dr. Ron Read of the University of Calgary faculty of medicine. He reported findings at the national beef science seminar in Calgary Nov. 16.
The study identified some strains of E. coli found in cattle as having a broad spectrum resistance to cephalosporins and ampicillin, a commonly used antibiotic in humans and animals. The study found no direct transmission of this type of resistant E. coli from cattle to people.
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“Ampicillin resistance itself is common among E. coli of both human and bovine origin,” said Read.
The team of researchers from the university and Agriculture Canada recommended cephalosporin resistance be studied further.
Beef producers requested the study because of concern over similar problems in Europe where antibiotic resistance among livestock occurred.
“If we are starting to see bacteria that are difficult to treat because of resistance that are arising from an agricultural setting, that is important to know,” said Read.
Antimicrobials are used to treat sick animals as well as provide protection against possible illness like liver abscesses. This practice is known as prophylaxis and several different types of antimicrobials are added to feed mixes.
The study examined the effect of commonly used treatments like tetracycline, tilmicosin, ceftiofur, florfenicol and ampicillin as well as medications found in feed such as monensin, tylosin, aureo-S-700 and aureomycin.
Problems appeared in Europe more than a decade ago when a drug called avoparcin led to antibiotic resistance in swine. It is similar to the powerful human drug vancomycin used to treat bacterial infections.
The study did not find feedlot cattle had vancomycin-resistant enterococci, or VRE, or methicillin-resistant staphylococcus aureus, said Read.
“While it has been speculated that VRE in humans in Europe arose from feeding subtherapeutic levels of avoparcin to livestock, this practice was never used in cattle in Canada. There is no evidence that existing feedlot practices promote or select for either of these two resistant organisms,” Read said.
“Furthermore, salmonella with multiple forms of resistance, reported to be found in outbreak situations in food animals, were not found in any of the feedlot animals we studied.”
The study focused on a single point in time, so ongoing surveillance is necessary, said Tim Guichon, a veterinarian with a feedlot health management service in Okotoks, Alta., who participated in the study.
“All intensive agriculture has come under scrutiny because of the antimicrobial resistance concerns that have been expressed by consumers,” he said.
Other food animal industries like pork and poultry may need to do similar studies to make sure their results are similar.
“If they are different, then they are going to have issues they are going to have to deal with,” Guichon said.
The beef industry moved ahead without knowing what the results might be and was prepared to make changes if necessary.
The issue is complex and people would like simple answers with predictable outcomes.
Scientists know cattle may pass certain bacteria like E. coli in their manure at different stages in their lives. There may be a two week period of heavy shedding and then the animals are healthy again.
“We’re just in the beginning stages of understanding what those processes are that might be contributing to that,” Guichon said.
The study was the most comprehensive of its kind and took five years, starting in 1999. Research was conducted at four Calgary-area feedlots and in research-model feedlots in Lethbridge.
Scientists collected samples from 2,622 feedlot calves upon arrival in the feedlot, during the feedlot period and before slaughter. They looked for a variety of conditions including salmonella, pasteurella, hemophilus and staphylococcus. Treatments provided to animals were also analyzed.
The team also collected samples from 60 feedlot workers to measure whether they acquired resistant organisms while working there. No problems among the staff were found.
