Pets eyed as carriers of antibiotic resistant bacteria

September 23, 2016

We have all heard about the increasing danger of antibiotic resistance in humans and farm animals, but now a new study by researchers in China is showing that our companion animals, such as cats and dogs, can also serve as a reservoir for antibiotic resistant bacteria. Because we spend so much time together (and sometimes even share our beds) with our pets, the transfer of this extremely dangerous bacteria can occur.

In this specific study, researchers found that a pet shop worker, along with four dogs and two cats in the shop where he worked, were infected with a strain of Escherichia coli (E. coli) bacteria carrying the MCR-1 gene—a molecule that can confer resistance to the last-resort antibiotic known as colistin.

"These findings suggest that MCR-1–producing E. coli can colonize companion animals and be transferred between companion animals and humans. The findings also suggest that, in addition to food animals and humans, companion animals can serve as a reservoir of colistin-resistant E. coli," the authors of the study wrote in a recent article.

The study was one of several in recent years to examine whether humans and pets can share drug-resistant bacteria. In 2014, researchers in the United Kingdom analyzing strains of methicillin-resistant Staphylococcus aureus (MRSA) in cats and dogs showed that humans and companion animals "readily exchange and share" isolates from the same strain, a finding that suggested pets and humans can pass MRSA "backwards and forwards," one of the authors said.

In addition, in a 2009 study investigators swabbed household surfaces at 35 randomly selected homes and found MRSA in more than half of them. In looking for factors that might make a home more likely to harbor the bacteria, they discovered that the presence of MRSA was eight times more likely in homes with cats.

So, does this mean pet owners be keeping a wary eye on their four-legged friends? Well, not necessarily, the article states, but the problem does appear to be increasing, experts said.

"Although the possibility of any disease is an important factor to think about, the risk is low, and often considered to be outweighed by the benefits of pet ownership," said Christine Hoang, DVM, assistant director of the Division of Animal and Public Health at the American Veterinary Medical Association.

Hoang and other experts agree that the potential clearly exists for resistance elements to move back and forth between humans and pets. But they said the risk of an individual getting a MRSA infection from their dog, to use one example, is very limited. Instead, the reverse scenario is more likely, given that MRSA strains exist in the nostrils of roughly one in three people.

Of greater concern is the increasingly drug-resistant gram-negative bacteria like E. coli and Salmonella, which can cause severe illness in humans. These pathogens could live in the guts of pets and be shed in feces, providing a possible avenue of transmission between pets and humans. "There's a bigger unknown factor with the gram-negatives, so I'm a little more concerned about them," Scott Weese, DVM, a veterinarian and microbiologist said in the article.

The problem is that very little research has been done in this area. When an individual acquires drug-resistant E. coli, for example, pets aren't generally looked at as the source of infection. "It's not on the radar," Weese added. Most funding agencies and governments, for good reason, are worried about food animals and food as sources of infection. "But they're forgetting the animals that we have the most contact with."

Good hygiene practices—not letting your pet lick your face, washing your hands regularly—are good precautions to take and pet owners can minimize their risk of infection by taking their pets to the vet for regular check-ups and vaccinations.

Just as in human medicine, there is also growing concern in the veterinary community about antibiotic overuse and overprescribing in companion animals. While there are no confirmed number on the rate of antibiotic overuse is in companion animals, some data suggests the amount of inappropriate is close to the most recent estimates in human medicine—50%.

In addition, experts are also concerned that companion animals are not included in the National Antimicrobial Resistance Monitoring System (NARMS), which tracks antibiotic resistance among Salmonella, Campylobacter, and other bacteria transmitted commonly through food. The article states that most veterinary teaching hospitals have mechanisms to monitor changes in resistance over time, but that there is a need for national surveillance of pets now more than ever before.

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