Antibiotic resistance profiles of oxytetracycline-resistant bacteria isolated from green mussel (Perna viridis)
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Antimicrobial resistance (AMR) is a growing global public health concern driven by the widespread use of antibiotics in human and veterinary medicine, including aquaculture. This study investigated the occurrence of oxytetracycline (OTC)-resistant bacteria associated with the green mussel (Perna viridis) collected from Dumangas, Iloilo, Philippines, a major aquaculture production area. Five freshly harvested mussels were processed for bacterial isolation using nutrient agar supplemented with OTC (20 µg/mL). Eleven OTC-resistant bacterial isolates were obtained and subjected to antibiotic susceptibility testing against seven clinically relevant antibiotics, followed by morphological, biochemical, and molecular characterization through 16S rRNA gene sequencing. The isolates showed varying resistance profiles, with the highest resistance observed against ceftazidime and chloramphenicol, while amikacin and gentamicin remained largely effective. Multiple antibiotic resistance (MAR) indices ranged from 0.14 to 0.71, with isolate GM06 exhibiting the highest MAR index (0.71), suggesting exposure to environments with high antibiotic selective pressure. Six representative isolates were further characterized and identified as Ureibacillus spp., Escherichia coli, Klebsiella pneumoniae, and Acinetobacter spp. Among these, the presumptive K. pneumoniae (GM06) and E. coli (GM05) demonstrated multidrug-resistant phenotypes. The presence of OTC-resistant and multidrug-resistant bacteria in P. viridis highlights potential food safety and public health risks, as filter-feeding bivalves can bioaccumulate antibiotic-resistant microorganisms from the surrounding environment. These findings underscore the need for stronger antimicrobial resistance surveillance in shellfish-growing waters and stricter regulation of antibiotic use in Philippine aquaculture systems to reduce the spread of resistance determinants and protect consumer health.
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