Colistin Resistance Profiles and Genotypes of Escherichia coli Isolates from Dogs and Cats
Authors: Sezener Merve Gizem , Findik Arzu , Ergüden Volkan Enes , Gülhan Timur , Ciftci Alper , Boynukara Banur 
Published: December 2024

Background: Nowadays, antibiotic resistance has become an important problem, posing a serious threat to both human and animal medicine. Colistin is one of the last-resort drugs for the treatment of particularly caused by multidrug resistant bacteria. The aim of this study was to investigate the resistance of Escherichia coli strains against colistin and the presence of colistin resistance genes (mcr1, mcr2 and mcr3) in them. Antibiotyping and genotyping of all strains was also aimed.
Materials, Methods & Results: A total of 75 isolates of Escherichia coli from healthy animals (38 dogs and 37 cats) were screened for colistin resistance by cultivation in a screening agar and then microbroth dilution method was performed. Antibiotic susceptibilities of the isolates were determined by KBDDM. The presences of mcr1, mcr2 and mcr3 genes were investigated by PCR. The colistin resistant strains were genotyped by using RAPD-PCR, and antibiotyped based on resistance profiles. In the screening test, 1 strain in cats and 2 strains in dogs were colistin-resistant. However, 18.6% of strains (from 14 cats and 3 dogs) were found as colistin-resistant in the microdilution test. MDR status was 76.31% and 97.29% in dog and cat strains, respectively. The colistin-resistant strains showed 78-100% and 65-90% similarities with respect to their antibiotypes and genotypes, respectively. mcr1, mcr2 and mcr3 genes were not found in any of the strains.
Discussion: There is an increase in infections brought on by Gram negative bacteria with various antibiotic resistances in addition to infections brought on by bacteria that are antibiotic-resistant. In order to cure illnesses caused by resistant bacteria, the repurposing of outdated antibiotics may be on the table. Colistin is a crucial antibiotic in veterinary medicine, according to a number of published perspectives, although it should only be administered with caution. However, the discovery of the plasmid-derived mcr1 gene and subsequent reports that this gene has propagated around the world. Escherichia coli strains isolated from companion animals have been found to carry the mcr1 (colistin resistance gene), and possible human-animal cross-contamination has been looked into. The findings demonstrated that mcr1-carrying E. coli might inhabit pets and spread between people and animals. The cat and dog strains used in this investigation had variable colistin resistance rates, which varied between trials. Although no isolates were found to be positive for the mcr1-3 genes in this study, it is believed that colistin resistance, which is determined phenotypically, should not be ignored in terms of spreading both in cat and dog populations as well as in terms of risk to human health, given the possibility that resistance could occur with other different mechanisms. Epidemiological research still uses in vitro antibacterial susceptibility patterns. Our antibiotyping method, which was based on an analysis of several antibiotic resistances, provided quantitative data. Commercial software was utilized to conduct the evaluation. There are no reports or publications that provide quantitative antibiotyping data for E. coli strains in the literature. A popular technique for genotyping different bacterial species is RAPD-PCR. By determining if certain specific genotypes are similar to those of other resistance strains, RAPD-PCR and other genotyping data can be compared with antibiotic resistance profiles to determine the specific risk of treatment resistance in infectious diseases. All organisms that were colistin resistant exhibited multiple antibiotic resistance, and these findings were also related to RAPD genotypes. The findings indicated that colistin-resistant E. coli bacteria could potentially represent a risk to human health and were thought to be transmitted from cats and dogs to humans and vice versa.
Keywords: antibiotyping, cats, colistin resistance, dogs, Escherichia coli, genotyping.