DNA helix2I’ve had a lot of emails over the past few months from colleagues from other countries, asking if we’re finding much mcr-1 in Canada. mcr-1 is a gene that makes bacteria resistant to colistin, a “drug of last resort” in people with some highly resistant infections.  The gene has emerged in bacteria from both animals and humans. It’s also been found a few times in a couple of different types of bacteria from food animals and food products in Canada.

This gene probably originated in food animals and is likely distributed in farm animals internationally, although only recently have researchers starting testing for it. I’ve been interested in the pet side, particularly following a report last year of mcr-1 in multiple dogs and cats in a Chinese pet store (after infection of a pet store employee was identified). When there was a large shipment of rescue dogs from China to Canada late last year, I would have loved to have tested some of the animals for mcr-1 in the bacteria they were shedding, along with various other things (for example, we know that multiple cases of distemper were associated with that particular group of dogs).

A recent paper in Emerging Infectious Diseases entitled mcr-1in Enterobacteriaceae from companion animals, Beijing, China, 2012-2016 highlights these concerns.

In that study (Lei et al, 2017) they tested Enterobacteriaceae from healthy and sick dogs and cats from Beijing’s Veterinary Teaching Hospital of the China Agricultural University. Enterobacteriaceae is a group of Gram negative bacteria, including most notably E. coli, Enterobacter, Salmonella and Klebsiella. The results were a bit scary:

  • 14% of the 566 isolates tested were resistant to colistin. This was mainly in E coli and Klebsiella.
  • 62% of the colistin-resistant isolates harboured mcr-1.
  • Bacteria that possessed mcr-1 were typically resistant to many other antibiotics, but were susceptible to some drugs.
  • Many different strains were involved, showing that this gene has moved to lots of different bacteria that have dispersed in the population.
  • 7/35 pet food samples (primarily chicken-based) were positive for mcr-1. What this means is unclear. Testing was done by PCR, which detects DNA, not necessarily live bacteria. So the bacteria containing mcr-1 could have been killed in cooking. But wow – that’s a concern, and further suggests that this gene may be highly prevalent in food animals.

Why was the colistin resistance rate so high? That’s an interesting question, since colistin is not used to treat dogs and cats (as opposed to food animals in some regions). It could reflect widespread exposure from food and the environment. It could also reflect use of other antibiotics in pets, since use of any drug to which the bacterium is resistant can select for that bug, and all its genes (e.g. if a bacterium is resistant to ampicillin and colistin, use of either drug will select for it).

What’s the threat to pets? Pretty minimal, since we don’t use colistin in pets.

What’s the threat to people? That’s the big question, since sharing of mcr-1 ­containing bacteria can definitely occur. The main concern is that pets might be a reservoir of mcr-1-carrying bacteria in households and the community. More work needs to be done to assess this risk, and look at mcr-1 in various species in other countries.