[Effects of long-term application of pig manure containing residual tetracycline on the formation of drug-resistant bacteria and resistance genes].

The effect of residual veterinary tetracycline on the formation of drug-resistant bacteria and corresponding resistance genes was investigated. During the research, the soil with long-term application of pig manure containing residual tetracycline was collected in autumn and summer respectively in the farmland around a certain pig farm in Shuyang City, Huang Huai area, north of Jiangsu province. At the same time, soils without application of pig manure in the farmland of this area were collected as the reference sample. Composition of drug-resistant bacteria in all soil samples was analyzed and three common tetracycline-resistance genes (tetA, tetC, tetE) were studied by PCR as well. During the research, 59 drug-resistant bacteria belonging to 13 bacterial genus respectively were separated from the soil sample collected in autumn while 35 drug- resistant bacteria belonging to 10 bacterial genus respectively were separated from the soil sample collected in summer and as for the reference sample, 3 drug-resistant bacteria belonging to 1 bacterial genus (Streptomyces) were separated with pathogenic bacteria up to 38.14% of total drug-resistant bacteria. PCR result showed that resistance genes were detected in all drug-resistant bacteria and tetC accounted for the most. At the same time, the residual tetracycline in the soil which was in a range of 41.1-61.9 microg x kg(-1) correlated with the amount of resistance genes (4.63 x 10(5)-37.42 x 10(5) copies x g(-1)). Besides, the climate was found accelerating the formation of drug-resistant bacteria and resistance genes.