| Dairy cow mastitis is one of the common diseases in dairy cows,and Streptococcus agalactiae is one of the important pathogens causing dairy cow mastitis.Streptococcus agalactiae adhesively invades the host body and destroys breast tissue and cells.Therefore,antibiotics are often used to treat cow mastitis caused by bacteria.However,with the increase of the isolation rate of Streptococcus agalactiae and the abuse of antibiotics,the drug resistance rate of Streptococcus agalactiae gradually rises.the purpose of this study is to understand the antimicrobial susceptibility of Streptococcus agalactiae isolated from cattle,and analyze the correlation between drug resistance phenotype and drug resistance genes of Streptococcus agalactiae,so as to provide theoretical reference for screening reasonable antimicrobial agents;determine the carrying status of virulence genes of Streptococcus agalactiae,and to explore the correlation between virulence genes and drug resistance of Streptococcus agalactiae.This experiment is divided into three parts:The first part: the drug sensitivity test of 16 kinds of antibiotics to Streptococcus agalactiae from cattle was carried out by broth dilution method,The results showed that the susceptibility of Streptococcus agalactiae from cattle to penicillin,amoxicillin/clavulanic acid,oxacillin,Cefalotin,ceftiofur,gentamicin,florfenicol,rifaximin,vancomycin,ciprofloxacin and compound sulfamethoxazole reached more than 65%,The drug resistance rate of ampicillin,erythromycin and clindamycin reached more than 50%,and the resistance rate to sulfamioxazole was also over 45%;In addition,the cases of multiple drug resistance were concentrated in 4,and the most serious multiple drug resistance was resistance to all the 16 antibiotics;and eight drug resistance genes were screened according to the drug sensitivity test,The common PCR method was used to confirm that Streptococcus agalactiae carried gyrA,sul1,erm B and erm C,and the coincidence rate of resistance phenotype and resistance gene was more than 79%.Part two: in order to understand the carrying of virulence factors of Streptococcus agalactiae from cattle,14 virulence genes of Streptococcus agalactiae were amplified,SPSS statistical software(22.0)was used to analyze the expression of virulence genes of Streptococcus agalactiae by one-wayANOVA and Duncan multiple comparison(P<0.05).The results showed that both multidrug-resistant and non multidrug-resistant strains carried eight virulence genes pavA,cfb,fbsA,bibA,cspA,sip,iagA and hyl B,however,bca,lmb and scp B were not detected.The detection rates of other virulence genes were different.The expression level of virulence genes in wild strain was significantly higher than that in standard strain.The third part: in order to explore the correlation between virulence genes and drug resistance,the results of drug resistance spectrum and virulence factors of Streptococcus agalactiae were statistically analyzed,the results showed that except for the eight virulence genes carried by both multidrug-resistant and non multidrug-resistant strains,the other three drug-resistant genes,cyl E,bac and rib,were different,indicating that these three virulence genes may be related to the drug resistance of Streptococcus agalactiae,so the correlation was analyzed by binary logistic regression model in SPSS statistical software(22.0),The results showed that there was no significant correlation between the virulence genes and drug resistance of Streptococcus agalactiae(P>0.05).According to the results of drug sensitivity test of Streptococcus agalactiae,Streptococcus agalactiae was sensitive to 11 kinds of antibiotics,but the most sensitive ones were ?-lactams and cephalosporins.The drug resistance rate of Streptococcus agalactiae to macrolides,sulfonamides and fluoroquinolones was high.Therefore,it is recommended that cattle farms should use drugs according to their own conditions in the treatment of Bacterial Mastitis,so as to achieve the best therapeutic effect,according to the carrying of virulence gene and the correlation between virulence gene and drug resistance,there was no significant correlation between them. |
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