Study On Detection Of ClassⅠIntegron Among Bovine Escherichia Coli And Resistance Mechanism To Florfenicol

In recent years, the resistance of Escherichia coli is becoming more and more serious. Several resistance mechanisms can co-exist, cooperate synergistically with each other inside a bacterial cell, which cause the complexity of resistance, and the complex resistances also increase the difficulties of clinical treatment. So the study of detection of integron and impact on drug pump of bacterial resistance of E.coli isolated from cow had an important significance to clinical treatment, and provided theoretical evidence for controlling the formation and propagation of bacterial resistance.In this study,245 strains of bovine E.coli isolated from cow in Ningxia were tested. K-B method was used to evaluate the resistance of the 245 strains of E.coli to 16 kinds of antimicrobials. The class I integrons of E.coli were detected by PCR. The drug susceptibility test result showed that the resistance rate of E.coli to ampicillin was the highest (51.48%). The resistance rates of streptomycin,tetracycline, doxycycline and chloramphenicol were also higher, they were 37.96%, 35.51%,36.33%,33.06% respectively. The resistance rate to norfloxacin was the lowest, only 7.16%. The integron test results showed that 35 strains of E.coli carried the class I integron, the detection rate was 14.29%.32 strains carriying 7 types of the integrated gene cassttes were detected in 35 integron-positive srtains, after sequencing analysis the gene cassette. It indicated that the dfrA and aadA which encoded aminoglycoside adenyltransferase and dihydrofolate reductase were in the majority. Of them, the gene cassette arrays dfrA17-aadA5 and dfrA7 were considerably epidemic.ESBLs genes of the 35 integron-positive E.coli were detected. The results showed that the detection rates of blaTEM, blaCTX-M, blaOXA were 88.57%,91.43%,14.29% respectively, while the blaSHV was not detected. In addition,24 strains of E.coli carried blaCTX-M and blaTEM gene at the same time,1 strain of E.coli carried blaCTX-M and blaOXA gene, and 4 strains of E.coli carried blaCTX-M, blaTEM and blaOXA gene simultaneously.FloR gene of 245 strains of E.coli was detected by PCR. The florfenicol accumulation in bacterial ample was determined by using HPLC method, in which the standard strains of E.coli(ATCC25922)and the strains resisting florfenicol and floR-positive were regarded as tested-bacterium. It showed that the detection rate of floR gene was 7.35%. The determination results indicated that the florfenicol accumulation of E.coli ATCC25922 was not influenced seriously while the florfenicol accumulation of florfenicol-resistant strains were strongly influenced by CCCP.In conclusion, in this study the resistance situation, prevalence of class I integron and resistance mechanisms to florfenicol of E.coli were revealed preliminarily by researching the resistance, the impact of class I integron and drug efflux pump forming resistance of E.coli. It provided theoretical evidence for monitoring the popular trend, controlling the formation, propagation of bacterial resistance and the research of resistance mechanisms of E.coli isolated from cow in Ningxia.