Investigation of colistin resistance in Escherichia coli isolated from dog feces

In this study, the faecal samples of 100 healthy and owned dogs of different age and sex from various districts of Istanbul were collected by rectal swab method, between November and December 2023. The samples were examined for the presence of E. coli by conventional bacteriological culture method. According to their appearance on MacConkey agar, 59 isolates (59%) were found to have E. coli suspicious colony appearance. Conventional biochemical tests (catalase, oxidase, citrate, indole, MR, urea, H2S formation in TSIA and carbohydrate fermentation tests) performed on suspicious isolates revealed that 59 isolates were E. coli. The 59 isolates identified as E. coli by conventional methods were confirmed by BD Phoenix™ M50 device. Susceptibilities of E. coli isolates were determined against fluoroquinolone, aminoglycoside, tetracycline, phenicol, sulphonamide, penicillin and monobactam group antimicrobials. In the results obtained, 18 isolates with resistance to three and/or more than three drug groups were considered as multidrug resistance positive. Broth microdilution method was used to confirm colistin resistance. Among 59 E. coli isolates obtained from dog faecal samples, phenotypic resistance to colistin was detected in only 1 isolate (1.69%). The results of this study indicate that colistin-resistant E. coli can colonise companion animals and be transferred between these animals and humans. The findings also suggest that, in addition to food animals and humans, companion animals may serve as reservoirs of colistin-resistant E. coli, adding another layer of complexity to the rapidly evolving epidemiology of plasmid-mediated colistin resistance in the community.