Carriage of antimicrobial-resistant E. coli in urban stray cats (Felis catus)

Antimicrobial resistance (AMR) in Escherichia coli is a growing concern in both human and veterinary medicine, driven by the inappropriate use of antimicrobials. Companion animals may act as community reservoirs and sentinels for antimicrobial-resistant bacteria due to their close contact with humans and other animals. However, resistance carriage in urban stray cats is poorly defined, particularly as many have limited direct antimicrobial exposure. This population provides an opportunity to assess baseline antimicrobial resistance carriage in companion animals with relatively low selection pressure. This study aimed to investigate the carriage of antimicrobial-resistant E. coli in the stray cat population in Perth, Western Australia. A total of 72 faecal samples from urban stray cats (May 2024-November 2024) were screened for carriage of antimicrobial-resistant E. coli. Chromogenic selective agars infused with antimicrobials were used to detect resistance to ampicillin (first line) and critically important antimicrobials (CIA), including ciprofloxacin and extended-spectrum cephalosporins. Presumptive E. coli were confirmed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) and tested by broth microdilution using the Robotic Antimicrobial Susceptibility Platform (RASP). Screening of 72 faecal samples yielded E. coli growth from 69 samples (95.8%). Of these, 37.7% (26/69) carried ampicillin-resistant E. coli, 1.4% (1/69) exhibited an extended-spectrum beta-lactamases phenotype, and no ciprofloxacin-resistant E. coli were detected. A total of 27 E. coli isolates underwent MIC testing, showing resistance to ampicillin (100%), cefotaxime (7.4%), ceftazidime (7.4%), sulfamethoxazole (33.3%), tetracycline (37.0%), and trimethoprim (29.6%). Ampicillin-resistant E. coli was common among urban stray cats, while no ciprofloxacin resistance was detected, suggesting low immediate CIA-related risk. However, the presence of extended-spectrum cephalosporin resistance, albeit at low levels, warrants further investigation given the potential for transmission and dissemination via mobile genetic elements. These findings indicate that urban stray cats can carry and potentially spread resistant bacteria despite their limited opportunities for antimicrobial exposure.