Occurrence of sulfonamide and tetracycline-resistant bacteria and resistance genes in aquaculture environment

The occurrence of sulfonamide and tetracycline resistance and their pollution profile in the aquaculture environment of Tianjin, northern China, were investigated. The presence of antibiotic-resistant bacteria was identified and the corresponding antibiotic resistance genes (ARGs) were quantified at 6 aquaculture farms in Tianjin. Sulfonamide-resistance genes were prevalent and their concentrations were the highest detected (3.0 × 10−5 to 3.3 × 10−4 for sul1/16S rDNA, 2.0 × 10−4 to 1.8 × 10−3 for sul2/16S rDNA) among the various ARGs, most likely because the use of sulfonamides is more prevalent than tetracyclines in this area. Bacillus was the most dominant bacterial genus in both sulfamethoxazole resistant bacteria (63.27% of the total resistant bacteria) and tetracycline-resistant bacteria (57.14% of the total resistant bacteria). At least two of those genes (tetM, tetO, tetT, tetW, sul1 and sul2) were detected in the isolates of Bacillus cereus, Bacillus subtilis, Bacillus megaterium and Acinetobacter lwofii, and all of the above genes were detected in B. cereus, suggesting the occurrence of multi-resistance in the studied area. The genetic transfer of sul1 between intestinal bacteria (e.g., Enterococcus spp.) and indigenous bacteria (e.g., Bacillus spp.) was implied by phylogenetic analysis. Several strains of resistant opportunistic pathogens (e.g., Acinetobacter spp.) were found in indigenous bacteria, which increase the risk of ARGs to public health. Overall, this is the first study to comprehensively investigate the antibiotic resistance profile by analyzing the species of antibiotic-resistant bacteria and adopting qualitative and quantitative methods to investigate ARGs at a typical aquaculture area in northern China.

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► We studied antibiotic resistance genes and resistant bacteria in aquaculture environment of Tianjin.
► Sulfonamide-resistance genes were prevalent.
► Bacillus was the most dominant bacterial genus in SMXr and TCr bacteria.
► Several strains of resistant opportunistic pathogens were found in indigenous bacteria.