Unveiling the spectrum of antibiotic resistance and virulence genes in Escherichia coli: A comparative study of clinical and environmental isolates

Multidrug resistant (MDR) Escherichia coli causing diarrhea and the spread of antibiotic resistance genes as well as virulence genes through aquatic MDR strains represent a major clinical concern worldwide. In this study, we examined the virulence gene contents and prevalence of multidrug resistance among Escherichia coli strains isolated from diarrheal patients and aquatic environment of Bangladesh. Clinical isolates from Mathbaria and environmental isolates from Dhaka (freshwater and wastewater) and Chittagong (marine-water) in Bangladesh were included. Herein, antibiotic resistance was examined using the disc diffusion method, while the screening of virulence genes was conducted through PCR assay. The results showed a high prevalence of multidrug resistance (MDR) among clinical isolates, with 90.91 % exhibiting MDR. Erythromycin resistance was observed in all clinical isolates, while mecillinam showed 100 % sensitivity. Significant resistance was also seen for ampicillin, azithromycin, and sulfamethoxazole-trimethoprim (>70 %) in clinical isolates. Among environmental isolates, 87.64 % were identified as MDR, with high resistance rates for erythromycin, ampicillin, and azithromycin. Geographic variations in resistance patterns were observed between Dhaka and Chittagong, with higher resistance in Dhaka for certain antibiotics such as Gentamycin (CN), Tetracycline (TE), Ciprofloxacin (CIP), Ampicillin (AMP), Cefixime (CFM), Mecillinam (MEL). Virulence gene prevalence differed between clinical and environmental isolates, with entero-toxigenic E. coli (ETEC) being dominant in clinical samples and Entero-invasive E. coli (EIEC) in environmental samples. Younger patients had significantly higher occurrence of virulence genes than older ones. No significant gender biasness was observed for the prevalence of antibiotic resistance and virulence. Comparative analysis showed Rampura isolates had the highest resistance and Mirpur isolates had the highest virulence gene prevalence. Results from sewerage samples showed significantly higher antibiotic resistance compared to river water isolates. In Chittagong, significant difference in resistance was noticed for the samples from Chatkhil and Patenga 1 zones, while virulence gene prevalence did not vary significantly. Overall, this study highlights the preponderance of MDR in clinical E. coli isolates and substantial antibiotic resistance and virulence genes in environmental isolates, particularly in non-coastal water sources. Therefore, effective antibiotic stewardship programs are crucial to combat resistance in clinical and environmental settings in Bangladesh.