Studies On Identification And Resistance Of Pathogenic E.coli Isolated From Bovine With Endometritis

Endometritis is one of genital system diseases which induce infertilitas of cows and often caused when postpartum uterus infected by pathogenic microorganism. Clinically, it was usually treated by using antimicrobial drugs. Under the antibiotic selective pressure, the drug resistant strains increased gradually, which not only interfere the development of animal husbandry ,but also produce potential threat to human health . In order to evaluate hazardness of pathogenic bacterium that caused bovine endometritis and direct to cure the disease rationally in clinic, the endometritis pathogenic E.coli isolated from Hohhot of Inner Mongolia were characterized for serotypes and antimicrobial susceptibility pattern.The results of the research showed,the isolating rateof E.coli from bovine endometritis was 54.3% ( 57/105 ) and the predominant serotype of them was O111:K58(B4)。The resistant rates of the isolates to sulfonamides, trimethoprime, tetracyclines,cefazolin,ampicillin,amoxicillin,kanamycin,streptomycin,chloramphenicol and polymyxin were higher,ranged in 50~98%, but the isolates were susceptible to ceftiofur, furazolidone and quinolones, the resistant rates were in 13.7~35% .The investigation and analysis on the molecular epidemiology of integrons/cassettes and different types of superspectrumβ-lactamase gene in these E.coli isolates were carried out by PCRand direct sequencing. The results indicated that 36.8% of them were positive for integronⅠand none of them carried integronⅡ,Ⅲ. Sequencing analysis revealed seven gene cassettes prevailed in Huhot surrounding region, which encoded resistance to trimethoprim(dhfr, dfrA1, dfrA17, dfr2d) and aminoglycosides (aadA1,aadA2,aadA5) respectively. Of them, the gene cassette arrays dfrA17-aadA5(69.1%) and dfrA1-aadA1(42.9%) were found most prevalent among these isolates.By analysis of resistant phenotype of 57 E.coli isolates and the character of molecular epidemiology of the integronⅠ/cassette, found that wether the isolates carried the integron /cassette was closely related to their level of multi-resistance. The isolates carried the integronⅠwere inclined to multi-resistance. The cassettes carried by the isolates could be explained their resistance to sulfonamides, trimethoprime, aminoglycosides. While, the resistant phenotype of the strains to the penicillins, tetracyclines and fluoroquinolones wasn't strongly correlated to whether the isolates carried the integronⅠ.The prevalence of the genes encoding CTX,SHV and TEM in E.coli isolates was investigated .The result showed blaTEM gene was predominant, the detection rate of it was 77.2% and there weren't the blaSHV,blaCTX gene. The resistant rates of isolates positive and negative for blaTEM gene toβ-lactam antibiotics were analyzed, found production and spread of ESBLS via plasmid were the important mechanism of the isolates' resistant toβ- lactam antibiotics. 95.2% of strains carried the integronⅠamplificated the blaTEM gene . It indicated distribution of classⅠintegron in ESBLS-producers contributed to disseminate drug resistance gene among bacterium.Subsequently, the mutations in the quinolone resistance-determining regions(QRDRS) of the gyrA, parC,gyrB and parE genes in 11 strains of the fluoroquinolone- resistant E.coli were analyzed by cloning and sequencing products of PCR. The result of the study showed that amino acid substitutions in GyrA of 4 mutants were Ser83→Leu,Asp87→Asn, in GyrB of 11 mutants was Pro385→Ala, in ParE of 2 mutants was Ser458→Ala. The amino acid substitutions in ParC, Ser58→Ile,Arg138→Asp,Arg138→Val,Pro140→Thr,Asn141→Lys were firstly reported to our knowledge. The research certificated the mutations in the QRDRS of the parC was the main mechanism of the isolates' resistant to fluoroquinolone in the area.