Abstract
Slaughterhouses are aimed at controlling organic matter and pathogens during animal processing; however, wastewater discharge often introduces microorganisms into the environment. This investigation focused on the isolation and characterization of thermotolerant Escherichia coli strains exhibiting pathogenicity, multidrug resistance, and biofilm-forming capacity from wastewater collected at the Kaptan Bazar slaughterhouse in Dhaka, Bangladesh. Seventy E. coli isolates were identified using selective culture media (MacConkey and eosin methylene blue agar) and PCR targeting the uidA gene. Antibiotic susceptibility was assessed using the Kirby-Bauer and modified Hodge methods. Biofilm formation was evaluated through the crystal violet assay. The presence of antibiotic resistance, virulence, and biofilm-associated genes was determined by conventional PCR. The most common virotypes were EIEC (7.14%), followed by ETEC (2.86%) and EHEC (1.43%). Extended-spectrum β-lactamase (ESBL) genes blaTEM (6.94%) and blaCTX-M-15 (2.78%) were detected. Carbapenem resistance genes included blaIMP-1 (3.70%), blaIMP-4 (1.85%), blaOXA-48 (21.76%), blaOXA-47 (0.46%), and blaOXA-1 (1.39%). Eleven isolates tested positive for carbapenemase production via the modified Hodge test. Non-β-lactam resistance genes detected included dfrA17 (25.46%), tetA (13.89%), sul2 (6.48%), qnrS (6.48%), and qnrB (3.24%). Class 1 integrons were present in 16 strains (22.86%), while both Class 2 and 3 integrons were absent. Colistin MIC values ranged from ≤ 0.5 to 2 μg/mL. Plasmid analysis showed that 59 isolates (84.29%) carried plasmids ranging in size from > 500 bp to > 10 kb. The crystal violet assay indicated that 74.29% of the isolates were biofilm producers, with 68.57% forming weak biofilms. Most weak biofilm formers and all moderate biofilm formers carried multiple antibiotic resistance genes. The results underscore a significant presence of antimicrobial-resistant and biofilm-producing E. coli in slaughterhouse effluents, highlighting the potential dissemination of ARGs into the surrounding ecosystem and food chains, posing a serious public health risk. The evidence also points to the urgent necessity for enhanced hygiene and treatment protocols to mitigate environmental and public health risks.