Bacteria remain resistant to antibiotics for years
Bacteria can remain resistant to antibiotics years after livestock producers stop administering them, according to a new study.
Science Now reports that researchers from McGill University studied the anaerobic bacteria in pig manure. Manure samples were taken from ten pigs, all out of the same sow, from the suckling to finishing stages.
The pigs were from a university farm that had banned antibiotics 2 ½ years prior to the study. Despite the lengthy ban, when scientists grew bacteria cultures in the labs, between 70 per cent and 100 per cent of them were still resistant to chlortetracycline.
Ecologist Martin Chénier, one of the lead researchers in the project, was surprised by the high levels of resistance. Researchers expected the bacteria to quickly lose resistance because the resistance genes are not part of the bacteria’s primary genome, and keeping them requires energy.
However, this isn’t the first study to document long-term resistance in bacteria. In 2002, a study out of the University of Kentucky found that 30 per cent to 70 per cent of the microbes remained resistant to tetracycline even though the antibiotics had been banned from the university since 1972.
The reasons for the resistance are unclear. Chénier thinks that the genes may be linked to other vital genes, such as the genes that protect pigs from high levels of zinc and copper. He also worries that spreading pig manure as fertilizer may spread antibiotic resistance to other microbes.
Such studies highlight the need for more research into drug-resistant microbes and food safety. Fortunately, there are several research projects in Canada doing just that.
Research projects examine pathogen shedding and survival, food safety
Dr. Leluo Guan and Dr. Paul Stothard are leading a team that is examining how zoonotic diseases pass from livestock to humans. The researchers are investigating how microRNAs affect zoonotic disease and shedding in pigs. They hope to develop software that can select pigs that shed fewer pathogens, cutting food contamination. More details are available on Genome Alberta’s website.
Meanwhile, another Genome Alberta project in Lethbridge is examining cattle that shed large amounts of E. coli. Tim McAllister and Brent Selinger head up a team that is examining how intestinal imbalances in cattle may cause them to shed more E. coli. They aim to develop strategies to reduce E. coli shedding, including bioactive compounds.
Researchers in Ontario are looking at survival rates of pathogens found in manure applied to fields. The Soil Resource Group is examining how application timing and methods of manure affect the survival of E. coli, salmonella and listeria. The group hopes to make recommendations on managing manure that will reduce the environmental impact and food safety risks of manure application. The initial research results are available in an interim report, found on Ontario Pork’s website.
Finally, a third Genome Alberta project seeks a method to use DNA to better trace ground meat back to the source during food recalls. Because ground beef contains the meat from many animals, it is often difficult to trace the finished product to the origin. Researchers plan to develop a system that will cut the amount of meat that has to be recalled due to contamination, while also making the recall more effective. The team is led by Professor Stephen Moore and Ciaran Meghen.