It is well known that recent antibiotic exposure is a risk factor for an animal’s infection being more resistant to antibiotics.1 We routinely ask owners whether a pet has recently been on antibiotics before devising an antibiotic plan for that patient. Newer evidence suggests that there is another equally important risk factor for developing an infection resistant to commonly used antibiotics: feeding a raw-food diet.
The first study linking a raw-food diet to cephalosporin resistance was published in 2008. This group intended to evaluate whether therapy dogs visiting patients in hospitals posed a risk to that vulnerable group of individuals. They found that the dogs in the therapy program who were fed raw meat within the year of the study were 17 times more likely to shed extended spectrum cephalosporinase E. coli than dogs in the program who were not fed raw diets.2 Because a common argument from raw diet proponents is that dogs are exposed to bacteria not through raw diets but treats (such as pig ears) the group controlled for dogs fed such treats and still found that feeding raw was a risk factor. More recently, 580 fecal samples were obtained from dogs in a cross-sectional study of dogs visiting vets in England. Of those samples, multi-drug resistant E.coli were found in 18.3% of samples, and the two risk factors for shedding of resistant organisms were previous antibiotic exposure and being fed a raw diet.3 In a cohort study of cats, it was found that cats fed a raw diet were 31 times more likely to shed extended-spectrum beta lactamase (ESBL) Enterobacteriaceae in their feces.4 In fact 89% of cats fed raw diets shed bacteria of this type which would be resistant not just to amoxicillin-clavulanic acid but also drugs designed to be resistant to beta lactamase such as second and third generation cephalosporins which are of critical importance in human medicine.4 Another study in dogs in the Netherlands showed that dogs fed raw meat were more than twice as likely to shed ESBL E. coli.5 The evidence is now overwhelming that feeding a raw diet increases the antibiotic resistance of enteric flora microbes. The question remains, however, how does this affect clinical decision making? Do we know whether having resistant flora in an animal’s GI tract leads to an anal sac abscess or a tooth-root abscess being resistant to amoxicillin-clavulanic acid? There are limited case reports that this may occur, and certainly when Salmonella is isolated, a link to a raw diet should be investigated.6 However, studies evaluating whether a raw diet leads to more resistant infections (as opposed to more resistant commensal flora) are lacking. What is a clinician to do with this information? I suggest three steps to avoiding treatment failure due to the risk posed by feeding a raw diet:
Ask clients whether they feed a raw diet for every case you see. Note whether the diet is home prepared or commercially prepared and whether it is freeze-dried or high pressure pasteurized (the latter two methods may reduce some but not all pathogens).
If a pet with an infection is fed a raw diet, perform an aerobic culture and educate the owner as to why an aerobic culture is warranted in this case. Make the link for them between raw diets, antibiotic resistance and the potential for treatment failure in this case.
In the case of life-threatening infections (examples: pneumonia, severe soft tissue infections leading to sepsis, abdominal sepsis, hepatic abscesses) where one cannot afford to be wrong in drug selection lest the patient die awaiting culture results, consider a de-escalation approach to antibiotic therapy.
A de-escalation approach to antibiotic therapy requires the clinician to choose drugs that are likely to kill the most resistant pathogens that COULD be causing the infection and then de-escalate to drugs that kill the isolated pathogens based on results of microbial culture. In the absence of culture results however, the clinician should de-escalate to a drug that is likely the kill most COMMON pathogens for the disease process after the animal has recovered to the point where the disease is no longer deemed life-threatening. An example of this approach is to put a dog with signs of SIRS suffering from oxygen-dependent aspiration pneumonia on ampicillin-sulbactam and enrofloxacin, but once the dog is no longer oxygen dependent and is eating and drinking, send the dog home on the oral form of just one of the two drugs. The idea that the animal has to “finish the course” of antibiotics is outdated and based on dogma and not scientific research, so stopping enrofloxacin, for example, after 2-3 days of in-hospital therapy is not only reasonable – but good antimicrobial stewardship.7
References and Recommended Reading
Weese JS, Giguère S, Guardabassi L, et al. ACVIM consensus statement on therapeutic antimicrobial use in animals and antimicrobial resistance. J Vet Intern Med. 2015;29(2):487–498. doi:10.1111/jvim.12562 *
Lefebvre SL, Reid-Smith R, Boerlin P, Weese JS. Evaluation of the risks of shedding Salmonellae and other potential pathogens by therapy dogs fed raw diets in Ontario and Alberta. Zoonoses Public Health. 2008;55(8-10):470–480. doi:10.1111/j.1863-2378.2008.01145.x
Schmidt VM, Pinchbeck GL, Nuttall T, McEwan N, Dawson S, Williams NJ. Antimicrobial resistance risk factors and characterisation of faecal E. coli isolated from healthy Labrador retrievers in the United Kingdom. Prev Vet Med. 2015;119(1-2):31–40. doi:10.1016/j.prevetmed.2015.01.013
Baede VO, Broens EM, Spaninks MP, et al. Raw pet food as a risk factor for shedding of extended-spectrum beta-lactamase-producing Enterobacteriaceae in household cats. PLoS One. 2017;12(11):e0187239. Published 2017 Nov 2. doi:10.1371/journal.pone.0187239 *
Baede VO, Wagenaar JA, Broens EM, et al. Longitudinal study of extended-spectrum-β-lactamase- and AmpC-producing Enterobacteriaceae in household dogs. Antimicrob Agents Chemother. 2015;59(6):3117–3124. doi:10.1128/AAC.04576-14
Kent M, Boozer L, Glass EN, Sanchez S, Platt SR, Freeman LM. Post-operative Salmonella surgical site infection in a dog. Can Vet J. 2017;58(9):936–940. *
Langford BJ, Morris AM. Is it time to stop counselling patients to “finish the course of antibiotics”?. Can Pharm J (Ott). 2017;150(6):349–350. Published 2017 Oct 5. doi:10.1177/1715163517735549 *
*Denotes articles that are Open Access and can be viewed online without a subscription.