Contamination of sulfonamide antibiotics and sulfamethazine-resistant bacteria in the downstream and estuarine areas of Jiulong River in Southeast China

Surface water samples from downstream and estuarine areas of Jiulong River were collected in August 2011 and May 2012 for detecting sulfonamide antibiotic residues and isolating sulfamethazine-resistant bacteria. Sulfamethazine was detected in all samples in May 2012 at an average concentration of 78.3 ng L−1, which was the highest among the nine sulfonamide antibiotics determined. Sulfamethazine-resistant bacteria (SRB) were screened using antibiotic-containing agar plates. The SRB average abundance in the samples was 3.69 × 104 and 2.17 × 103 CFUs mL−1 in August 2011 and May 2012, respectively, and was positively correlated to sulfamethazine concentration in May 2012. The 16S rRNA gene sequencing of all the 121 SRB isolates revealed high diversity. Furthermore, the SRB isolates exhibited multidrug resistance, with 48.7 % showing resistance to at least three antibiotics. The abundance and persistence of highly diverse SRB and their multidrug resistance are likely to demonstrate the transferable pressure from coastal environments on public health.