Abundance and Distribution of Tetracycline Resistance Genes and Mobile Elements in an Oxytetracycline Production Wastewater Treatment System

We investigated the abundance and distribution of tetracycline resistance genes (tet genes) in an oxytetracycline (OTC) antibiotic production wastewater (APW) treatment system. Of sixteen tet genes and five mobile elements, nine tet genes (tet(A), tet(C), tet(G), tet(L), tet(M), tet(O), tet(Q), tet(W), and tet(X)) and two mobile elements (class 1 integron (intI1) and transposon Tn916/1545) were successfully quantified by real-time PCR. The relative abundance of tet genes in the effluent and activated sludge (1.2 × 10–4 to 1.3 × 100) of the APW treatment system were up to 2 orders of magnitude higher than those in the OTC fermentation residues (8.5 × 10–5 to 6.7 × 10–3) (P < 0.01), and 1–4 orders of magnitude higher than those in sewage and nonantibiotic production wastewater treatment systems (P < 0.01), showing that the discharge of abundant tet genes from the APW treatment system is worthy of attention. The three most abundant genes in the APW treatment system, tet(A), tet(C), and tet(G), exhibited significant positive correlations with intI1 (R 2 = 0.73, 0.95, and 0.83, respectively; P < 0.05), suggesting that intI1 may be involved in their proliferation. This is the first study showing that some measures may be required to control the discharge of antibiotic resistance genes from treated APW and activated sludge.