| Aminoglycoside antibiotics is a kind of spectrum and highly effective antibiotics which has good antimicrobial activity to bacteria. But this kind of antibiotics are widely used in clinical, the new drug resistance mechanisms appeared-16S rRNA methylase, which lead to the growing number of clinical drug resistant strains and increased the resistant rate. In addition, there has been appeared the multi-resistant strains which was in combination with β-lactamases and quinolone antibiotics, seriously affected the use of aminoglycoside antibiotics in clinical. Thus, the study on dissemination mechanism of 16S rRNA methylases among Escherichia coli isolated from cow in Ningxia not only has guiding significance for rational clinical use of drug, but also help to reduce and control the spresd of drug-resistant among E.coli.This study mainly collected samples from subclinical or clinical cases of bovine mastitis and feces of part dairy farm in Ningxia. The methods including gram staining microscopy, CHROMagar E. coli agar and PCR amplification for 16S rDNA gene were used for the isolation and identification of E.coli. The MICs of 16 antimicrobial agents for E.coli isolates were determined by the broth microdilution method according to the guidelines recommended by the Clinical and Laboratory Standards Institute(CLSI). And the disk diffusion method was used for ESBLs phenotype confirmation of E.coli isolates. The results showed that 245 strains of E.coli were isolated and identified, and the isolation rate was 19.48%. The results of susceptibility testing showed that the highest proportion of resistance was towards ampicillin (51.84%), followed by streptomycin (37.96%), doxycline (36.33%), tetracycline (35.51%) and cefazolin (30.20%). The relatively susceptible antimicrobials were polymyxin, fluorine, aminoglycosides, cephalosporins and quinolones, and the sensitive rate was more than 60%. All isolates tolerated up to 16 kinds of antimicrobial agents. After the phenotype confirmation test,60 strains of 245 E.coli were detected carrying ESBLs, and the detection rate was 24.49%(60/245).16S rRNA methylases genes and ESBLs genes of 245 E.coli isolates were detected by PCR. The results showed that only rmtB gene were detected among 16S rRNA methylases genes and the positive rate was 5.3%(13/245). The positive rates of blaTEM, blaCTX-M and blaoXA among ESBLs genes were 23.27%(57/245),11.02%(27/245) and 2.86%(7/245).Additionally, the 13 rmtB-positive isolates were examined for blaTEM-1, blaCTX-M and blaoXA-1, and the positive rate was 100.0%(13/13), 100.0%(13/13)and 15.38%(2/13) respectively.By the methods of PFGE, Conjugation experiments and Southern blotting were used for the research on dissemination mechanism of 16S rRNA methylases genes, respectively from the horizontal and clonal transmission. The results suggested that both clonal expansion and horizontal transmission contributed to the spread of rmtB gene among E.coli isolated from cow in Ningxia.In conclusion, we analysed drug resistance of E.coli isolated from cow in Ningxia and researched on dissemination mechanism of 16S rRNA methylases genes. It revealed that the drug resistance situation and the molecular epidemiological characteristics of E.coli from dairy farm in Ningxia and the dissemination mechanism of 16S rRNA methylases genes among E.coli. Provide theory basis for using antimicrobials rationaliy and reducing and controlling the spread of drug-resistant E.coli and resistant genes. |
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