Combination of antibiotics suppressed the increase of a part of ARGs in fecal microorganism of weaned pigs

The presence of antibiotic resistance genes (ARGs) is one of the most important public health concerns. Six tetracycline resistance genes (TRGs— tet A, tet C, tet L, tet O, tet W, and tet X) were quantified using real-time quantitative polymerase chain reaction (qPCR) in the fecal microorganisms of weaned pigs. Two hundred 35-day-old weaned pigs were fed different dietary antibiotics for 28 days: (1) no antibiotic as the control treatment (CT); (2) chlortetracycline, bacitracin zinc and colistin sulfate (CBC); (3) bacitracin zinc and colistin sulfate (BC); and (4) chlortetracycline (CTC). The detection frequencies (DFs) of tet C, tet L, and tet W were 100 %; and the DFs of tet A, tet D, tet M, tet O, and tet X were 65 %. The relative abundances ( tet /16S rRNA gene copy numbers) of six tet genes ( tet A, tet C, tet L, tet O, tet W and tet X) were between 1.5 × 10 −4 and 2.0 × 10 −1 . In the group CTC, the relative abundances of tet C ( P < 0.01), tet L ( P < 0.01), tet O ( P < 0.05), tet W ( P < 0.01), and tet X ( P < 0.01) were greater than those of the group CT. Compared with the group CTC, the relative abundances of tet C ( P < 0.01), tet L ( P < 0.01), and tet W ( P < 0.01) were decreased in the CBC and BC groups. These results indicate that a combination of different antibiotics suppressed the abundance increase of a part of tet genes, which suggests that a combination of antibiotics produces multiple selection pressures on fecal microorganism of pigs.