Does Antibiotic Use in Dogs Lead to Resistance in Humans?

The need to address and fight antimicrobial resistance is an important One Health issue. The FDA’s Center for Veterinary Medicine, for example, recently published its 5-year plan to address antimicrobial stewardship in veterinary settings.

As presented at ID Week 2018 in San Francisco, CA, investigators from Tufts University Cummings School of Veterinary Medicine set out to analyze the impact on humans of treating dogs with amoxicillin-clavulanate. In particular, could prolonged use of an antibiotic lead to resistance in both dog and owner?

The pilot study was inspired by the growing One Health concern that the continued use of antibiotics in pets can contribute to colonization by resistant organisms in their owners. This was, in part, based the knowledge that colonization with resistant pathogens can be transmitted from companion animals to their owners.

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Methodology

Eight pairs of dogs and their owners were enrolled in the study. Participants were considered eligible if the dog had visited the Foster Hospital for Small Animals emergency department in North Grafton, MA and had an infection that required 14 days of amoxicillin-clavulanate therapy. Additionally, the owners had to live in the same household and have frequent contact with the dog; oral contact was not a requisite. Also, the owners could not have taken any antibiotics within 30 days of the study.

Stool samples were collected from each dog and its closest adult human owner at the initiation of antibiotic administration and again at the end of the 14-day course. The samples were semi-quantitatively cultured for enteric flora and tested for ampicillin-sulbactam resistance (A/S-r), ciprofloxacin resistance (CIP-r), extended-spectrum beta-lactamases (ESBL), methicillin-resistant Staphylococcus aureus (MRSA), and vancomycin-resistant Enterococcus (VRE) on day 1 and subsequently on day 14.

Results

Upon study enrollment, enteric flora was present in all 8 human—dog pairs. Two of the 7 dog samples that could be analyzed had no detectable enteric flora on day 14. Throughout the study, no humans or dogs acquired MRSA or VRE. However, 1 human lost colonization with CIP-r flora, and 2 dogs acquired CIP-r during antibiotic treatment but did not transmit it to their owners. One dog and 1 unrelated human acquired ESBL colonization by day 14 that was not present on day 1.

In total, 3 human subjects were colonized with A/S-r on day 1 that then persisted through the treatment period. Of their 3 corresponding dogs, 1 had no A/S-r at either time point, 1 acquired high counts of A/S-r flora, and 1 did not provide enough stool at day 14 for testing. One other dog acquired A/S-r flora and 1 dog had increasing counts of A/S-r; in both instances the human owners had no A/S-r on day 1 or 14.

Conclusions

Upon analysis, the investigators concluded that the use of amoxicillin/clavulanate can lead to resistant colonization in the dog taking antibiotics. Furthermore, their close human owners may share or transmit colonization. In 2 cases, resistance may have been transmitted from the pet owner to the dog as a result of increased vulnerability caused by the derangement of gut flora by antibiotics. The investigators noted that additional studies are currently underway.