Antimicrobial Resistance Characteristics of Escherichia coli Isolated from Commercial Tilapia Farms: A Study from a Major Fish Production Hub in Bangladesh

Abstract

In aquaculture, antimicrobials are commonly used to prevent and treat infections in fish; however, injudicious antimicrobial use (AMU) can pose significant risks, including the emergence of antimicrobial-resistant pathogens in aquatic environments. This study was carried out to assess the occurrence of drug-resistant Escherichia coli in tilapia (Oreochromis niloticus) collected from 41 commercial tilapia farms located in five upazilas (Fulbaria, Trishal, Phulpur, Tarakanda and Mymensingh Sadar) of Mymensingh, Bangladesh, between December 2022 and April 2023. A total of 153 samples, including skin (n=41), gill (n=41), intestine (n=30), and farm water (n=41) were analyzed. The E. coli isolates were isolated and then identified using the E. coli-specific uidA gene by means of polymerase chain reaction (PCR). Antimicrobial susceptibility testing (AST) was conducted by means of Kirby Bauer disk diffusion method with 14 antimicrobials to determine the antimicrobial resistance (AMR) patterns, and the results were interpreted by Clinical and Laboratory Standards Institute (CLSI) guidelines. In addition, the multiple antimicrobial resistance (MAR) index was calculated to determine the extent of multi-drug resistance in E. coli. A total of 31 E. coli isolates (20.26%) were identified, with the highest prevalence in the intestine (32.26%), followed by skin (29.03%), water (25.81%), and gill (12.90%). The isolates were mostly resistant to ampicillin (93.55%), nalidixic acid (38.71%), and oxytetracycline (32.26%). Conversely, more than 80% of the isolates were susceptible to chloramphenicol, meropenem, norfloxacin, gentamicin, azithromycin, levofloxacin, and cefepime. The MAR index values ranged from 0 – 0.71, with 38.71% of the isolates classified as multi-drug-resistant isolates, indicating selective pressure within the aquaculture environment. These findings highlight the possible risk of transmitting AMR bacteria through the aquatic food chain and emphasize the necessity for prudent AMU in aquaculture.