Occurrence of antimicrobial resistance, integrons and virulence genes in Escherichia coli isolated from drinking water in Van, Turkiye: a cross-sectional study

Abstract

Background: Escherichia coli is one of the recommended freshwater indicator organisms for faecal contamination and can be associated with the pool of genes encoding antibiotic resistance. The aim of this study was to investigate the molecular characterisation of antibiotic resistance and to identify the virulence genes in E. coli isolated from drinking water samples collected for the purpose of monitoring microbial drinking water quality. Methods: The E. coli isolates (n = 244) from municipal tap water samples collected in Van province in Turkiye over a five-month period in 2018 were examined in this study. Antimicrobial susceptibility testing was performed using the standard disc diffusion method with 12 antibiotics. Integron content, the resistance genes such as blaTEM, blaSHV, blaCTX-M groups, tetA-E genes, qnrA, qnrB, qnrS, qepA, and aac(6’)-Ib-cr were screened and the virulence genes (afa, sfa, fimA, hly, iroN, aer, cnf, iutA and pap) were assessed by specific PCRs. The fingerprinting of the isolates harbouring the integron was evaluated using dendogram analysis of the band patterns obtained from the enterobacterial repetitive intergenic consensus (ERIC) PCR. Results: Ampicillin, tetracycline, streptomycin, nalidixic acid and trimethoprim/sulfamethoxazole were the most common resistances. MAR index of 18.03% of the isolates was greater than 0.2. The two isolates produced ESBL. Thirty seven (15.16%) isolates carried the class 1 or class 2 integrons harboured the gene cassettes such as aadA, sat, estX and unnamed protein gene. Thirty two (21.47%) isolates were found to carry blaTEM, 5 (3.33%) isolates carried blaSHV and 2 (1.3%) isolates carried the blaCTX-M group genes. tetA (81.25%) and tetB (91.66%) were present in tetracycline-resistant isolates. qnrS (29.92%), qnrB and aac(6’)-Ib-cr (3.84%) were present in the nalidixic acid resistant isolates. Most of the isolates carried the virulence genes such as fimA, iutA, iroN, aer and sfa. Isolates belonged to 65.57% B1, 15.98% A, 9.42% D and 9.01% B2 phylogroups. A statistically significant difference was found between the phylogenetic groups of the isolates and the integron content (p < 0.001). Fingerprinting showed the 25 different phylotypes in four clusters. Conclusions: Molecular epidemiological findings in such a five-month period in the 11 sampled districts in the city of Van appearently showed us that the tap waters in public use was continuously contaminated by the antibiotic resistant and virulent E. coli isolates. This could pose a serious public health risk and, thus need the serious precautions for the infrastructures.