Srudy On Antibiotic Resistance And Resistant Mechanism Of Bovine E.Coli

Pathogenic Escherichia coli (E.Coli) is an important pathogen bacterial of white diarrhea of bovine. In recent years, the resistance of E.coli to antimicrobial agents has been rapidly increasing in many countries of the world. Up to now ,in many countries and areas, plenty data on resistance and genetyping distributeion of E.coli has been collected; besides, spread of E.coli resistance was investingated by various moleculear biology methoes. These data contributed a great deal in treatment and prevention of E.coli infection. However, few data of E.coli has been reported regarding the prevalence and spread of E.coli resistance in HeiLongjiang. We collected clinical isolates and carriage strains of E.coli around HeiLongjiang, determined the drug resistance and gene typing. To make a compareison of between the results of gene typing and the resistance phenotype.26 strains of calf E.coli were isolated from different farms by general method and biochemistry characteristic around HeiLongjiang. All isolates were examined to better understand the prevalence of antibiotic resistance using K-B method suggested by WHO. Antimicrobial susceptibility testing of 13 antimicrobial agents was performed on the isolated strains, and the testing results that 8 kinds of antibiotics were resistant. Based on the NCCLS results, streptomycin, amoxicillin, tetracycline, trimethoprim-sulfamethoxazole, doxycycline's drug resistant rates were always 100% in fore four position, DOX's was 96.15%. And to gentamycin, amikacin, polymyxin, neomycin and ciprofloxacin, norfloxacin, enrofloxacin, 26 strains performed highly sensitive(100%) to the fore four position, to ciprofloxacin's drug resistant rate was 7.69%, and respectively norfloxacin's was 11.54%, enrofloxacin's was 3.85%, and chloramphenicol's was 19.23%. So the strains multidrug resistance of E.coli were serious.The prevalence of the genes encoding CTX-M, TEM and SHV in E.coli isolayes was investingated. Two different genotypes were detected among these ESBL positive isolates by PCR: CTX-M-positive(19.23%), TEM-positive(84.62%). The generation and dissemination of plasmid-mediated ESBLS led to the important mechanism of resistance that the isolates toβ-lactam antibiotics; 2 kinds of AMES genes includeing aadA1 and aac(3)-â…¡were presented in E.coli strains: aadA1(73.33%) and aac(3)-â…¡(11.54%). The results showed that the main mechanism for bacteria to produce a modified passive drug enzymes, namely aminoglycoside modifying enzymes (AMEs)-related; Chloramphenicol resistance gene test results showed: cmlA gene positive rate of detection wad 45.15%, floR gene positive rate of detection was 19.23%, and the strain that contain floR gene will resist to the strains that contain non-enzyme-resistant gene cmlA. The emergence of these resistant strains is bound to create difficulties for clinical treatment. Should be noted that clinical use of drugs and control it`s trend.Subsequently, the mutateons in the quinolone resistance-determining regions(QRDRS) of the gyrA, gyrB and parC genes in 4 strains of the fluoroquinolone-resistane E.coli were analyzed by cloning and sequenceing products of PCR. The result of the study showed that amino acid substituteions in GyrA of 1 mutant was Ser83â†'Leu; in Theamino acid substituteions in ParC, Ser80â†'Arg,Ile were reported to our knowledge. The research certificated themutations in the QRDRS of the GyrA,ParC was the main mechanism of the isolates'resistant to fluoroquinolone in the area.Pulsed-field gel electrophoresis(PFGE) was for the gene typing of E.coli, we have conducted the following research: comparison of between the results of gene typing and the results of drug resistance phenotype. 26 strains scattering in different bovine farms were classified to 10 gype by PFGE. A group could be further divided into B1, B2 and B3 subtypes. There were none-related correlation between resistance phenotype and PFGE: A comparison of PFGE results with resistance results indicated that antibiotic resistance patterns varied considerably within several individual E.coli clones, and antibiotic resistance patterns resembled within differentiated E.coli clones, but the same PFGE electrophoresis spectra that had the same drug resistant spectra of the strains had a higher probability of occurrence. The conclusion was that Vertical transmission of resistant E.coli clones for farm animals were commonly occurs.