Prevalence of sulfonamide-resistant bacteria, resistance genes and integron-associated horizontal gene transfer in natural water bodies and soils adjacent to a swine feedlot in northern Taiwan

Antibiotics are commonly used in swine feed to treat and prevent disease, as well as to promote growth. Antibiotics released into the environment via wastewater could accelerate the emergence of antibiotic-resistant bacteria and resistance genes in the surrounding environment. In this study, we quantified the occurrence of sulfonamides, sulfonamide-resistant microorganisms and resistance genes in the wastewater from a swine farm in northern Taiwan and its surrounding natural water bodies and soils. Sulfonamide levels were similar in the receiving downstream and upstream river water. However, the prevalence of sulfonamide-resistant bacteria and resistance genes, as analyzed by cultivation-dependent and -independent molecular approaches, was significantly greater in the downstream compared to the upstream river water samples. Barcoded-pyrosequencing revealed a highly diverse bacterial community structure in each sample. However, the sequence identity of the sulfonamide resistance gene sul1 in the wastewater and downstream environment samples was nearly identical (99-100%). The sul1 gene, which is genetically linked to class 1 integrons, was dominant in the downstream water bodies and soils. In conclusion, the increased prevalence of sulfonamide resistance genes in the wastewater from a swine farm, independent of the persistent presence of sulfonamides, could be a potential source of resistant gene pools in the surrounding environment.