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More answers on antimicrobial resistance

Results from three component studies reveal the details behind the most comprehensive research project to date examining the issue of antibiotic resistance in cattle and the potential for transfer of this resistance to humans

The bottom line of Canada's most extensive research project examining antimicrobial resistance in beef cattle was great news for the beef industry: The use of antimicrobial drugs in Canadian cattle production is not currently a major contributor to the development of resistant bacteria that threaten human health. (Click here for a summary of overall findings on the antimicrobial resistance study.)

Dr. Ron Read, lead researcher on the antimicrobial resistance project, answers reporters' questions at the National Beef Science Seminar.

But that finding shouldn't change the goal of reducing antimicrobial use in the beef industry, says Dr. Tim McAllister of Agriculture and Agri-Food Canada (AAFC) in Lethbridge, one of the lead researchers on the Canada Alberta Beef Industry Development Fund (CABIDF) project. Results of three component studies reveal important facts that suggest important improvements to antimicrobial management. Read the brief highlights below, and click on the links for greater detail in new Research Reports available on the CABIDF Web site.

Aureo S-700 connection

In this component, researchers designed experimental pen studies to examine the development of antibiotic-resistant Escherichia coli (AREC) in feedlot steers receiving sub-therapeutic levels of antibiotics.

They concluded that feeding antimicrobials to steers did not promote ciprofloxacin or gentamicin resistance in enteric E. coli, but tetracycline and ampicillin resistance were increased when chlortetracycline and sulfamethazine (Aureo S-700) was fed. "This finding correlates closely with the observations in the commercial feedlot study," says McAllister. See Research Report.

Containing transient bacteria

This component study was conducted to determine the incidence of transfer of a naturally occurring rifampicin-resistant strain of Escherichia coli (RREC) among cattle in a research feedlot.

The researchers showed that faecal-oral transmission was likely responsible for the observed movement of the organism between penmates. However, there was no significant movement of this strain between pens and, in the absence of antibiotic pressure, shedding of the organism occurred for only a short period after acquisition.

"These results suggest that widespread transfer of a resistant organism throughout a feedlot is not necessarily a foregone conclusion, particularly without any antibiotic selective pressure," says Sam Stevenson, a M. Sc. graduate student from the University of Lethbridge, who worked on the study. "The results also provide us with knowledge for developing strategies to better contain transient bacteria that may enter the feedlot environment." See Research Report.

Managing resistant Campylobacter

In this component, Dr. Doug Inglis of AAFC Lethbridge and his colleagues showed that routine use of antibiotics in feedlot cattle did produce Campylobacter species resistant to antibiotics.

Substantial development of resistance to both tetracycline and doxycycline was observed. "This is not totally surprising given the extensive use of tetracyclines in the feedlots we monitored," says Inglis. "Doxycycline is an antibiotic that belongs to the same chemical class as tetracycline." See Research Report.

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