Evaluation of resistance to colistin and aminoglycosides in Escherichia coli isolated from broilers in Guilan province

Chicken meat, as one of the most important sources of protein in the world, shows a high rate of contamination with Escherichia coli, which can widely spread antibiotic resistance. The aim of this study was to investigate the resistance to colistin and aminoglycosides in E. coli isolated from broilers. In this study, during 2021, a total of 122 E. coli isolates were collected from the heart and liver of 20- to 45-day-old chickens with clinical signs of colibacillosis. Aminoglycosides and colistin resistant strains were identified by disk diffusion and MIC determination, respectively. Subsequently, the presence of mcr-1, mcr-2, mcr-3, aph (3′)-IIa, aac (3) -IIa and ant (3″)-Ia genes in the isolates was analyzed by PCR. Out of 122 isolates, 35 isolates (28.68%) were resistant to neomycin sulfate and 1 isolate (0.82%) was resistant to gentamicin. All isolates were sensitive to amikacin, tobramycin and streptomycin and 5 isolates (4.10%) were resistant to the colistin. In the detection of mcr genes by PCR method, none of the studied genes were identified, but aph (3′) -IIa, aac (3) -IIa and ant (3″)-Ia genes were detected in 25.41%, 23.77% and 36.88% of isolates respectively. The results of this study indicate a decrease in the sensitivity of poultry isolated E. coli to aminoglycosides and colistin. The spread of such resistant isolates is a serious warning about the reduction in treatment choices of colibacillosis and indicates the risk of transmission of resistance genes to the human microbial flora.