Research Of Drug Resistance And Resistance Genes Of Salmonella And Escherichia Coli

Salmonella and Escherichia coli are the important pathogenic bacteria. Due to the large-scale and unreasonable use of antibiotics, serious multi-drug resistance had appeared in Salmonella and E. coli, most of existing drugs are invalid. The resistance gene mediated by plasmid can transfer to other animals and humans, which not only leads to enormous economic losses to breeding industry, but also brings on some problems to food safety and human health. Therefore, to understand the resistance situations and resistance genes of Salmonella and E. coli and to know the resistant mechanisms, it can provide scientific basis for clinical medication and drug administration of veterinary and theoretical foundation for development of new antibiotic drugs. In this study Salmonella and E. coli were isolated and identificated by using the national standard method. The drug resistance of isolated strains of Salmonella and E. coli to 12 antibiotics had been tested by broth microdilution method and the situation about carrying and transforming of resistance genes had been tested by PCR. Meanwhile, the genetype, drug resistance and the resistance genes of Salmonella and E. coli from the corresponding samples had been compared in the study. The main conclusions are summarized as follows:1. There are 293 E. coli isolated from 400 samples, the isolation rate is 73.3%,136 strains are from pig and 157 strains are from chicken. There are 38 Salmonella isolated from 334 samples, the highest detection rate is 26.5% from entrails of dead pigs in Liaoning, the pig slaughterhouse in Anhui and the few farmers markets in Beijing ranked as the second and third, the detection rate is 11.0% and 7.0% respectively.2. There are eight serotypes by identification, respectively, S. derby (44.7%), S. enteritidis (26.3%), S. rissen (10.5%), S. typhimurium(1.9%), S. litchfleld (2.6%), S. lansing (2.6%), S. daytona (2.6%) and S. tennessee (2.6%). Genetype analysis by PvuⅡ and EcoR Ⅰ to Salmonella and E. coli from the corresponding samples shows that the genetypes of E. coli are more than Salmonella obviously, Salmonella from the same serotype have various high homology genetypes, different serotype of Salmonella from the same area appears high homology genetypes.3. The drug resistance of isolated E. coli and Salmonella to 12 common antibiotics is different. The drug resistant of E. coli from pig and chicken is also different to some antibiotics. The resistant trend of Salmonella and E. coli from the corresponding samples is similar. The MIC distribution of Salmonella and E. coli has obvious moveright to some antibiotics of serious drug resistance in our country compared with the EUCAST standard, which indicates the drug resistance is more serious in our country than European Union. Overall, Salmonella and E. coli to sulfonamides, tetracyclines, aminoglycosides and chlomycetins are serious resistant, but to P-lactam and fluoroquinolones are relative sensitive. The multi-drug resistance is very serious, more than 80% E. coli and all Salmonella resist three antibiotics at least, mainly resist seven, eight and nine antibiotics.4. PCR is used to test some drug resistance gene of Salmonella and E. coli from the corresponding samples. The results show that there are no cmy, oxa shv and tetM gene amplificated from all strains. The rate of carrying tem gene of 20 Salmonella and 19 E. coli which are β-lactam drug resistance is 75.0% and 68.4% respectively. The rate of carrying sull, sul2, sul3 gene are 43.3% and 31.1%,33.3% and 28.1%,16.7% and 18.7% respectively in 30 Salmonella and 32 E. coli which are sulfonamides drug resistance. The rate of carrying tetA gene is 76.3% and 81.6% respectively in 38 Salmonella and 38 E. coli which are tetracylines drug resistance. The rate of carrying aadA and aac(6’)-Ib-cr gene are 34.5% and 40.7%, 41.4% and 33.3% respectively in 29 Salmonella and 27 E. coli which are aminoglycosisdes drug resistance. The rate of carrying floR gene is 83.3% and 87.5% respectively in 30 Salmonella and 24 E. coli which are chloromycetins drug resistance.5. Gene mutation of DNA gyrase and topoisomerase is the important mechanism to gram negative bacteria showing drug resistance to fluoroquinolones antibiotic.7 strains are Ser83Ala mutation of gyrA gene,2 strains are Asp87Asn of gyrA gene,4 strains are Ser83Ala and Asp87Asn mutation of gyrA gene and 2 strains are Asp83Ala mutation of gyrA gene and Ser80Arg mutation of parC gene in 15 strains of Salmonella with drug resistance to fluoroquinolones.9 strains are Ser83 Ala mutation of gyrA gene,5 strains are Asp87Asn of gyrA gene and 3 strains are Ser83Ala and Asp87Asn mutation of gyrA gene in 17 strains of E. coli with drug resistance to fluoroquinolones.6. The transform conjugation test of floR gene verified that resistance gene mediated by plasmid can transfer between Salmonella and E. coli. The recipient strain of E. coli showed same drug resistance phenotype with donor strain of Salmonella due to obtained resistance gene from donor strain.