Antibiotic-resistant pathogens and heavy metal-tolerant bacteria in Batissa violacea: A study from the Ba River, Fiji

The Ba River in Fiji is a critical livelihood source for bivalve harvesters, yet increasing anthropogenic activities threaten the safety of its aquatic food sources. This study comprehensively examines the microbial communities associated with freshwater bivalves (Batissa violacea) and river sediments, focusing on antibiotic resistance and heavy metal (HM) tolerance. Samples from soft tissues, gills, and sediments were subjected to Most Probable Number (MPN) tests, antibiotic susceptibility assays, HM tolerance analysis, and 16S rRNA gene sequencing to identify microbial taxa and their functional characteristics. Several pathogenic bacteria were isolated and identified, including Vibrio cholerae, Vibrio parahaemolyticus, Salmonella spp., and thermotolerant Escherichia coli. Most isolates exhibited multidrug resistance, particularly against rifampicin, vancomycin, penicillin, streptomycin, and tetracycline, posing potential risks to public health and food safety. Conversely, HM tolerance analysis revealed limited microbial resistance to zinc, copper, cadmium, chromium, and lead, predominantly at concentrations of 1 mM. The presence of these antibiotic-resistant and HM-tolerant microbes underscores the critical interplay between environmental contamination and microbial evolution, presenting challenges for both ecosystem health and human consumption safety. The findings highlight the urgent need for integrated environmental management and interventions to mitigate microbial contamination in aquatic systems.