Resistance Gene And Virulence Gene Analysis Of Staphylococcus Aureus From Bovine Mastitis

Staphylococcus aureus is one of the main pathogens causing mastitis in dairy cows,there is no effective vaccine so far to prevent it,antibiotics are still the only medium to prevent and treatment Staphylococcus aureus.There are drug resistance to many antibiotic drugs for Staphylococcus aureus,and because of the nonstandard use of antibiotics,the phenomenon of multi-drug resistance is becoming more and more serious,it brings enormous trouble to treatment of infections caused by S.aureus.Find out the characters of drug-resistance,drug resistance gene and virulence gene,it is of significance to prevent the S.aureus.This study isolated four strains of Staphylococcus aureus from clinical mastitis bovine milk in a cattle farm of Liaoning Province.The purification,identification and drug sensitive test of the four strains were tested,and analyses the resistant gene,virulence gene they carried.The study lay an experimental base for resonable prevention and treatment of dairy cow mastitis in this cow farm.This study deals with isolation and cultivation of the pathogen of milk from clinical mastitis dairy cows,then received S.aureus through biochemical identification and molecular identification.Adopted 12 antibiotic commonly used in veterinary clinic resistance of Staphylococcus aureus isolates were detected by using disk agar diffusion method,and learn about the resistant phenotype.The results showed that four strains of Staphylococcus aureus were isolated and identified,and each strain has different characteristics of drug resistance.The resistances of Staphylococcus aureus isolates to azithromycin,tetracycline and lincomycin are high,and sensitive to amoxicillin and levofloxacin.Overall,aminoglycosides and quinolones bacteriostasis effect is very obvious.About multiple resistance,4 strains were resistant to a variety of antibiotics.Isolates N2-1 was resistant to 7 antibiotics,isolates N2-2and N3 were resistant to 4 antibiotics,isolates N1 was resistant to 3 antibiotics.The multi-drug resistance of these isolates was severe.PCR was used to detect 7 resistance genes of 4 Staphylococcus aureus isolates.Tetracycline resistant genes tet M and macrolides resistant genes erm B were found.Isolates N2-1 carries resistant genes tet M,isolates N2-2 carries resistant genes erm B,isolates N3 carries resistant genes tet M and erm B.Resistant genes erm B positive rate is the same as the positive rate of erythromycin resistant phenotype.About the detection of virulence genes,methods PCR method was used to detect 7virulence genes of 4 Staphylococcus aureus isolates,include enterotoxins,exfoliative toxin,hemolysin,panton-valentine leucocidin and exfoliative toxin.The results showed that virulence genes were detected in all four isolates.Isolates N1 and N3 carries hemolysin virulence genes hla and hlb,isolates N2-1 carries virulence genes hla,isolates N2-2 carries virulence genes hlb.Virulence genes sea,seb,eta,pvl,tsst were not found.In animal experiments,after drug attacks,the experimental mice produced different degree clinical symptoms.Through pathological examination,the mammary gland of most mice is destroyed,other organs did not appear significant pathological changes.The results of pathogen detection shows,the main pathogens causing mastitis in the cattle farm were Staphylococcus aureus which carrying resistant genes tet M,erm B and virulence genes hla,hlb.The result of resistance analysis shows,aminoglycosides and quinolones bacteriostasis effect is very obvious,these drugs can be selected to used for clinical treatment.