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Researchers find mcr-1 in pet food in China
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Recently, researchers in China said companion animals such as dogs and cats may harbor the mcr-1 gene and pass it to humans. Now, researchers think they know where pets are acquiring the gene: in their food.
During a study to estimate the prevalence of mcr-1 in Enterobacteriaceae from dogs and cats in Beijing, Timothy R. Walsh, DSc, professor in the department of medical microbiology and infectious disease at Cardiff University in Wales, and colleagues also tested a small sample of pet food and discovered that 20% of the samples contained mcr-1 — a plasmid-mediated gene that has raised alarms because of its ability to confer resistance to colistin. It has been found in people and food-producing animals in more than 30 countries on five continents.
In a letter published in Emerging Infectious Diseases, Walsh and colleagues said their research shows that “frequent and close contact” between humans and their pets presents opportunities for colistin-resistant Enterobacteriaceae to be passed between them.
“Because we found mcr-1 in pet foods, we speculate that the pet food industry may be a source of mcr-1 among companion animals,” they wrote.
The food chain is a main route of transmission for humans and pets to acquire foodborne pathogens such as Enterobacteriaceae, which may contain the mcr-1 gene. Walsh, who was part of the research team that first documented mcr-1 in 2015 during a routine antimicrobial resistance surveillance project in China, previously told Infectious Disease News that China would begin banning the use of colistin in animal feed starting on April 1 but start using it in humans to treat infections caused by MDR gram-negative pathogens like carbapenem-resistant Enterobacteriaceae.
After researchers in China documented the case of a pet shop worker whose mcr-1–positive Escherichia coli isolates matched those taken from four dogs and two cats at the shop where he worked, Walsh and colleagues tested 1,439 nasal and rectal samples collected from healthy and sick dogs and cats at a veterinary teaching hospital in Beijing from 2012 to 2016. The animals were from an urban area of Beijing with little or no contact with food-producing animals that may have been given colistin.
The samples from 1,254 dogs and 185 cats contained 566 nonduplicate strains of Enterobacteriaceae, including 14% that were resistant to colistin and 8.7% that harbored the mcr-1 gene. Among 79 colistin-resistant isolates, 62% (n = 49) harbored mcr-1 — 49 E. coli and two Klebsiella pneumoniae isolates.
Walsh and colleagues also tested 32 nasal swabs from pet owners, turning up 25 Enterobacteriaceae. One E. coli isolate from a pet owner was resistant to colistin and harbored mcr-1. The isolate matched five that were taken from dogs and cats. “These results suggest that pet foods may be a source from which intestinal bacteria of companion animals can acquire the mcr-1 gene,” Walsh and colleagues wrote.
They tested 30 dog food samples and five cat food samples — all containing chicken as the main ingredient — and found seven were positive for mcr-1, including five produced by companies in China. The results suggest that intestinal bacteria of pets can acquire the gene from pet food, Walsh and colleagues said.
“Because of frequent and close contact between humans and companion animals, our study proposes that opportunities exist to transmit colistin-resistant Enterobacteriaceae to and from both groups,” they concluded. “Thus, colistin-resistant Enterobacteriaceae from companion animals may represent a potential risk to human health. Further surveillance and control efforts are needed to reduce colistin-resistant and mcr-1–containing Enterobacteriaceae in companion animals and food-producing animals.” – by Gerard Gallagher
Disclosure: Please see the full letter for a list of the authors’ relevant financial disclosures.
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