Antimicrobial resistance profiles of presumptive Escherichia coli isolated from wild-caught tilapia (Oreochromis sp.) in Iloilo River, Iloilo, Philippines
Antimicrobial resistance (AMR) remains a growing global threat to human, animal, and environmental health. Aquatic environments have become important reservoirs and transmission pathways for antimicrobial-resistant bacteria due to increasing anthropogenic pressures. Escherichia coli, a common commensal bacterium in humans and animals, is widely used as an indicator organism for AMR surveillance and poses environmental and public health concerns when resistant strains are present. However, wild and apparently healthy fish remain underrepresented in AMR research. In this study, apparently healthy wild tilapia (Oreochromis sp.) were collected from the Iloilo River. Gut, kidney, liver, and spleen samples were plated to obtain bacterial isolates. Presumptively identified E. coli based on biochemical testing were subjected to antimicrobial susceptibility testing against 11 antibiotics representing seven classes. The highest resistance rates were observed for ampicillin, cefotaxime, and tetracycline. The average multiple antibiotic resistance (MAR) index was 0.09, with four isolates exhibiting multidrug resistance and six identified as potential extended-spectrum ?-lactamase (ESBL) producers. Although the MAR index indicates relatively low antimicrobial selective pressure, the detection of multidrug-resistant E. coli in wild, apparently healthy fish underscores their potential as sentinels of antimicrobial resistance in the river system. Further studies are warranted to characterize the genetic determinants and resistance mechanisms contributing to environmental AMR.
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