Occurrence And Fate Of Tetracycline Resistant Genes In Livestock Manure,Compost And Soil

All mankind are faced with bacterial resistance which is one of the most pressing public health problems. The migration and fate of antibiotic resistance genes are increasingly concerned by researchers that emerge as an environmental pollutant. As a kind of typical broad spectrum antibiotic, tetracycline is more widely used in livestock breeding industry in our country. The study on typing and drug-resistant mechanisms of tetracycline resistance genes are more thorough, but the migration and fate of drug resistence genes in the environment is still far more enough. Therefore, with lactose fermentation bacterium (LFE) as research object, this study analyzed the distribution of tetracycline resistance genes (tet-R) in the tetracycline resistant Lactose-fermenting Enterobacteriaceae (TR-LFE), and the abundance of tetracycline resistance genes (tet-R) derived from livestock manure, compost and soil in the two pig farm and chicken farm in Shanghai based on traditional microbial culture and modern molecular biotechnology. The findings are as follows:(1) The proportions of the TR-LFE to LFE in pig manure, pig manure compost and soil applying pig manure compost were with the trend of decrease, as well as in chicken manure and chicken manure compost.(2) Among the 540 and 340 TR-LFE strains isolated from the samples in the pig farm and chicken farm respectively, selecting different drug resistence mechanisms of specific primers of ten tet-R genes, the tet-R genes of isolated strains were detected by ordinary PCR method.lt was found that there were 485 and 289 strains carrying one or more of the detected tet-R genes in the samples of pig farm and chicken farm, respectively.(3) According to the detection rates, the 10 kinds of tet-R genes detected positive in the pig farm ranked in order with tet(A), tet(B), tet(M), tet(G), tet(C), tet(D), tet(S),tet(O), tet(X) and tet(E). while the ten kinds of tet-R genes detected positive in the chicken farm ranked in order with tet(A), tet(B), tet(M), tet(D), tet(G), tet(O), tet(C), tet(S), tet(X) and tet(E).The efflux pump gene tet(A) and tet(B) and the ribosomal protection protein gene tet(M) were the main genes in pig manure, compost and soil,and also widespreding in chicken manure,compost.(4)The highest detection rates of double tet-R genes in pig manure, compost and soil were tet(A)+tet(B), tet(A)+tet(M) and tet(B)+tet(M), which generally appeared in all the samples.While the highest detection rates in chicken manure and compost were tet(A)+tet(M) and tet(A)+tet(B).Different sources of TR-LFE carrying single tet-R gene of the detection rates order for young pig manure>adult pig manure>soil>pig manure compost, and multiple tet-R genes detection rates of size sequence for pig manure compost>soil>adult pig manure> young pig manure. The pig manure compost not only with the highest detection rate of multiplex tet-R genes but also with the most types of multidrug resistence genes.Pig manure compost and chicken manure compost were aslo with the most kinds of tet-R genes.(5) According to the detection rates, the tet-R genes detected in the total DNA of samples in the pig farm ranked in order with adult pig manure, young pig manure, compost and soil; and the detection rates in the chicken farm were with the order of adult chicken manure, young chicken manure and compost(6) The content of tet(A) and tet(C) in the samples of pig farm and chicken farm were detected by fluorescence quantitative polymerase chain reaction (qRT-PCR).The results showed that the content of tet(A) and tet(C) genes in pig manure compost were with 0～3 and 1～4 orders of magnitude lower than fresh pig manure,respectively, while soil was with 0～1 orders of magnitude lower than pig manure compost. The content of tet(A) and tet(C) genes in chicken manure compost were with 0～4 and 1 ～3 orders of magnitude lower than fresh chicken manure,respectively. Therefore, it was suggesting that tet-R genes were gradually decreasing in livestock manure, compost and soil, and the compost process may be benefical to the decrease of tet-R genes content.