Occurrences and distribution of sulfonamide and tetracycline resistance genes in the Yangtze River Estuary and nearby coastal area

The role of highly impacted estuaries needs to be examined with respect to the spread of antibiotic resistance genes in the environment. In the present study, sulfonamide resistance (sul), tetracycline resistance (tet) and class I integron (int1) genes were ubiquitous in the sediments of the Yangtze Estuary (YE) and nearby coastal area, and exhibited a declining trend from the inner estuary to the coast. Good relationships were only observed between int1 and sul1 genes, implying that int1 gene is essential to the proliferation of sul1 gene. A non-significant correlation between int1 and 16S rRNA genes indicated that the int1 gene came from pollution sources of ARGs instead of being intrinsic in environmental bacterial populations. Sulfonamides were rarely detected in the sediments of this region, so could not result in the production of sul genes in the local environment.