Dissemination of resistance genes in duck/fish polyculture ponds in Guangdong Province: correlations between Cu and Zn and antibiotic resistance genes.

Duck/fish polyculture farming is a typical farming model in the Pearl River delta in southern China. We examined soil, water, and sediment samples from three duck-fish farms in Guangdong Province in September and December 2014. We determined the abundance of three metal resistance genes, 16S rDNA, and 23 antibiotic resistance genes encoding resistance to tetracycline, sulfonamides, quinolones, chloramphenicol, and β-lactamases. Microbial community structure was quantified by Illumina high-throughput sequencing of 16S rDNA genes. We found a prevalence of antibiotic resistance genes and the sul1, sul2, tetA, tetM, aac(6')-Ib, and floR genes were the most abundant. Levels of Cu and Zn were significantly correlated with numerous ARG types and sul2, floR, and tetM were identified as potential antibiotic resistance gene indicators. Cu levels were significantly and positively correlated with the relative abundance of sul3, tetT, tetW, qnrB, qnrS, fexB, sul1, sul2, tetM, and qnrA. Zn was significantly correlated to relative abundance of sul2, sul3, tetM, tetA, tetT, tetW, qnrA, qnrB, qnrS, aac(6')-Ib, qepA, bla, cmlA, floR, fexA, cfr, and fexB. The levels of Acinetobacter, Brevibacillus, and Wautersiella showed significant positive correlations with metal resistance genes as well as qnrB, oqxA, oqxB, and bla (p > 0.8). Sphingobacterium, Flavobacterium, Acidothermus, and Corynebacterium had significant correlations with abundance of tetracycline resistance genes, sulfonamide resistance genes, bla, bla, and cfr (p > 0.8). Sphingobacterium, Flavobacterium, Acidothermus, and Corynebacterium were most abundant in soil samples while Acinetobacter, Brevibacillus, and Wautersiella were most abundant in water samples. Dissemination of antibiotic resistance genes in aquaculture environments is extensive and tracing their origins is necessary to establish risk assessment methods required for aquatic environmental protection.