Antibiotics and Antibiotic Resistance Genes in Coastal Marine Sediments Near Aquaculture Sites in Rivers State

The proliferation of antibiotic use in Nigerian aquaculture has raised concerns about the environmental fate of antibiotics and the spread of antibiotic resistance genes in coastal marine sediments. This study investigated the concentrations of commonly used aquaculture antibiotics and the diversity of antibiotic resistance genes in coastal marine sediments adjacent to intensive fish farming operations in Rivers State. Sediment samples were collected from five aquaculture-proximate sites and two reference sites during wet and dry seasons. Antibiotic residue analysis for oxytetracycline, ciprofloxacin, amoxicillin, and sulfonamides was performed using ultra-high-performance liquid chromatography-tandem mass spectrometry. Antibiotic resistance gene abundance was quantified using quantitative PCR targeting 16 resistance gene families. Total bacterial community composition was profiled using 16S rRNA gene metabarcoding. Oxytetracycline was the most frequently detected antibiotic, present in all aquaculture-proximate sediments at concentrations ranging from 12.3 to 167.8 micrograms per kilogram. Ciprofloxacin was detected at concentrations exceeding ecotoxicological threshold values at three of five sites. Aquaculture-proximate sediments harboured significantly higher abundance and diversity of antibiotic resistance genes compared to reference sites. Tetracycline and sulfonamide resistance genes were most abundant. Correlation analysis confirmed that oxytetracycline concentration was the strongest predictor of tetracycline resistance gene abundance. Bacteroidetes-associated resistance gene integrons were elevated at all aquaculture sites. The study documents for the first time the extent of antibiotic and resistance gene contamination around Nigerian coastal aquaculture and recommends a national antibiotic stewardship policy for the aquaculture sector. Keywords: antibiotic resistance genes, aquaculture sediments, oxytetracycline, Rivers State, antimicrobial resistance.