| In the last 20 years, Listeria monocytogenes was recognized as zoonotic pathogens. Its pathogenicity is the strongest in Listeria spp., and it is the only typical intracellular parasitic bacterium which is pathogenic to human, not only can cause meningitis, encephalitis, sepsis, endocarditis, abscesses and localized purulent damage, but also can cause pregnant women abortion, stillbirth and so on. Its mortality rate is higher, up to 30% or more. With the continued application of clinical antimicrobial drug prevention and treatment of this disease, one or more of drug resistance strains of L. monocytogenes were found. Tetracycline-resistant strains were the earliest and the highest resistant L. monocytogenes. Studies had shown that tetracycline-resistant L. monocytogenes carried the resistance gene tetM. TetM gene often associated with plasmids, transposons by which to transfer between bacteria, and it could transfer between L. monocytogenes and also from L. monocytogenes to E. faecalis. But so far, at home or abroad there is no one to report that tetM gene in L. monocytogenes could transfer to other pathogenic bacteria. Therefore, in order to further explore horizontal transfer of tetracycline-resistant gene of L. monocytogenes, to stop the spread of bacterial resistance and provide a theoretical basis for new antimicrobial drug development, horizontal transfer of tetM gene of L. monocytogenes that isolated from fresh meat bought in the market in Harbin were studied.A total of 23 L. monocytogenes were isolated and identified from 158 fresh meats in the market in Harbin by three methods of Coloration medium, API reagent strip and PCR. The positive rate was 14.56%. Among them, the positive rate of fresh pork was the highest, reaching to 20.00%.3 L. monocytogenes of tetracycline-resistant were screened from 23 strains by diffusion method. Other 20 kinds of antibacterial drugs were determined too. The result showed that 100% strains were susceptible to Cafalotin. The resistance rate of Polymyxin B is highest, up to 65.2%. The resistance rate of Norfloxacin Cefotaxime, Fosfomycin, Lincomycin, and Nitrofurantoin is more than 30.0%. 1 of 23 isolated strains was susceptible to 21 kinds of antibacterial drugs; other strains were resistant to one or more antibacterials. Among them, 21.7% of strains were resistant to one antibacterial; 13.0% were resistant to two; 4.4% were resistant to three; 8.7% were resistant to four; 26.1% were resistant to five; 8.7% were resistant to six; 4.4% were resistant to seven; 8.7% were resistant to fifteen. Strains resisted to more than two kinds of antibacterials were reached to 17.Tetracycline-resistant gene was determined from 3 L. monocytogenes by PCR method. TetM gene was amplified from 3 L. monocytogenes. It showed that tetracycline resistance is related to tetM gene closely.A tetracycline-resistant strain of L. monocytogenes D38 as the donor was conjugated to an erythromycin-resistant strain of Streptococcus suis B22 as a recipient. Transconjugants were identified by PCR methods. Resistant spectrum of recipient B22 was determined before and after the conjugation, and tetM gene sequence of donor D38 was compared before and after the conjugation. There were 19 transconjugants on TSA-YE medium containing erythromycin and tetracycline, and conjugative transfer rate was 3.8×10-7. Cps gene, ermB gene and tetM gene were specific amplified from 19 transconjugants, which showed tetM gene of donor strain D38 were transferred to recipient strain B22. All 19 transconjugants were resistant to tetracycline, and tetM gene of transconjugants shared 100% nucleotide homology with that of donor D38.
|
PDF Full Text Request