The Danger Lurking in Raw Pet Foods

Antimicrobial resistance is a global problem in human and veterinary medicine. Extended-spectrum beta-lactamase (ESBL)— and AmpC beta-lactamase (AmpC)–producing bacteria contribute to this resistance and transmit their resistance-conferring genes through plasmids. ESBL/AmpC-producing Enterobacteriaceae (ESBL-pE) has been identified in several sources, including food animals, which poses a major concern for human health. The Enterobacteriaceae family contains Escherichia coli.

ESBL-pE has also been isolated from companion animals. Previous studies have reported similarities in ESBL-pE strains between humans and companion animals. Such findings raise the question of whether direct contact with animals or their feces increases the risk for antimicrobial resistance transmission.

Raw pet food (RPF) consumption has been considered a potential risk factor for ESBL/AmpC shedding in companion animals. In addition, previous studies have reported ESBL-pE within RPF products. To date, however, no studies have investigated an association between RPF consumption and ESBL/AmpC shedding. The current study, recently published in PLoS ONE, reported this association, demonstrating that RPFs are “an important risk for ESBL/AmpC shedding in household cats,” the study investigators wrote.

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Analyses

Thirty-six unrelated pet cats were divided into 2 experimental groups according to commercial diet type: non-RPF (control group, n = 17) and RPF (exposed group, n = 19). The investigators selected 35 non-RPF and 18 RPF diets for the study.

The cats’ owners fed the assigned diet type, completed a questionnaire, and submitted a once-weekly fecal sample for 3 consecutive weeks. In total, 108 fecal samples were collected (51, control; 57, exposed).

Fecal samples were first cultured on agar plates with cefotaxime. Bacterial colonies then underwent further genetic analyses to identify and characterize the bacterial species and genes. The 53 commercial pet foods underwent similar culture and genetic analyses.

Results

Fecal Sample Analysis

Approximately 65% of fecal samples were culture-positive in the exposed group, compared with only 6% in the control group. Fecal bacteria concentrations were higher in the exposed group.

Investigators identified 135 E coli isolates, 114 of which had ESBL/AmpC-encoding genes. Eighty-one isolates contained the bla_CTX-M genes; previous studies have noted that CTX-M beta-lactamases, which are among the most frequently isolated ESBLs, have played an important role in the evolution of antimicrobial resistance. The specific bla_CTX-M genes identified in the current study were similar to those found in food animals, which was expected given that poultry and beef are common protein sources in pet food.

Statistical analysis indicated a strong association between RPF consumption and ESBL-pE fecal shedding, making “RPF a probable source of ESBL/AmpC shedding in companion animals,” the investigators wrote. Factors such as other in-contact animals and predation habits were not significantly associated with ESBL-pE fecal shedding.

Food Analysis

Nearly 80% (14/18) of the RPF diets contained ESBL-pE. None of the non-RPF diets contained this bacterium.

Implications

Taken together, this study’s findings highlight “the risk of feeding raw pet food to companion animals for both the animals as well as their owners handling raw pet food,” concluded the investigators. They advised that pet owners be made aware of the risk of ESBL-pE transmission when handling raw pet food.

Dr. Pendergrass received her Doctor of Veterinary Medicine degree from the Virginia-Maryland College of Veterinary Medicine. Following veterinary school, she completed a postdoctoral fellowship at Emory University’s Yerkes National Primate Research Center. Dr. Pendergrass is the founder and owner of JPen Communications, a medical communications company.