Epidemiological Investigation Of Drug Resistance Genes Of Bovine-derived E.coli And Application Of Drug Resistance Mutation Selection Window

Antibiotic is the indispensable drug to control infection in clinical,it was found that can achieve good curative effect in animals after in human,thus the application of antibiotics is becoming more common in aquaculture industry but leaded the drug resistance to enhance with the use of large doses for a long time,the result was difficult to cure bacterial infection.E.coli is one of the important pathogenic bacteria causing animal diseases such as diarrhea,sepsis clinical in clinic,carry the cilia adhesion antigen such as F17 that settled in the intestinal mucosa,easy cause of the fatal disease such as calf diarrhea,cow mastitis,metritis cause the huge losses to broad masses of farmers.At present,the research focus is how to prevention and cure colibacillosis.The use of antibiotics generally based on the MIC,and using single medication in clinical,makes the bacteria easy to acquire resistance.With the deepening of the research,drug combination according to the theory of MSW can reduce the generation of bacterial drug resistance.The study was based on the theory of MSW,combinate CTX with ENR.It showed that Cefotaxime combined Enrofloxacin can contract even close the mutant selection window and prevent the formation of drug resistance.To study the effect of antibiotics combination on the mutant selection window(MSW)of Escherichia coli from cattle with F17 virulence gene,11 strains with F17 virulence gene were isolated from the clinical wild strains.The sensitivity of 19 kinds of antibiotics was determined by the K-B experiment method and determined 21 drug resistance genes by PCR.The results showed that drug resistance present situation is not optimistic:they were multiple in drug resistance of 11 strains,at least 4 heavy resistance,up to 17 heavy resistance,the highest percentages of resistante rate was 81.8%of S,the lowest percentages of resistante rate was 0%of PB,secondly the percentages of resistante rate was 18.2%of AZT;the percentages of resistante rate of AM?AMX?CL?GM?DOX?OT?FFC?SXT?CIP?LMF?ENR?NOR exceed 50%,the percentages of resistante rate of CFX?CRO?CTX?K less than 50%.The testing results of resistance gene show that detection rate of tetA?tetB?GyrA was 100%,detection rate of blaTEM?parC was 90.90%,doing multiple drug resistant genes strains statistics found six strains carrying five types of resistant genes,one strains carrying four types of resistant genes,four strains carrying three types of resistant genes;for the single resistant genes,the highest detection rate of tetA?tetB?GyrA was 100%,take second place was blaTEM?parC(90%),the detection rate of aacC2 was above 50%,other resistant genes were low.After the MIC of Cefotaxime(CTX)and Enrofloxacin(ENR)sole and combined were determined by the method of micro dilution method and checkboard test.The result showed that the MIC of some strains were declined,the MIC50 of all strains were declined but the MIC90 weren't.The mutant prevention concentration(MPC)sole and combined were determined by the method of agar plates dilution method,and the value of SI(selection index:MPC/MIC)was acquired.The results showed that the MPC90 of Cefotaxime dropped to 256mg/L,the value of SI decreased by 4 fold and the MPC90 to MIC90 ratio was 1,which indicated that the MSW was closed after Cefotaxime combined with Enrofloxacin.Whilst the MPC90 of Enrofloxacin was reduced to 256mg/L,the value of SI decreased by 2 fold and the MPC90 to MIC90 ratio was 2,which demonstrated that the MSW was narrowed.The study showed that Cefotaxime combined Enrofloxacin can contract even close the mutant selection window and prevent the formation of drug resistance.