Research On Antimicrobial Susceptibility And Molecular Characteristics Of The Main Pathogen From Bovine Mastitis

Objectives Bovine mastitis is a kind of inflammatory reaction caused by various pathogens invading the bovine mammary.The disease not only caused huge economic losses to the dairy industry in the world,but also brought severe challenges to public health and food safety.The aim of this study was to investigate the antimicrobial susceptibility and molecular characteristics of the main pathogens from 202 bovine mastitis samples collected from mastitis cases in China,so as to provide new ideas for the prevention and treatment of bovine mastitis and the development of new antibiotics.Methods1.The identification of 202 samples were identified by microscope examination and 16 Sr DNA sequence.2.The antimicrobial susceptibility and biofilm formation ability of 123 E.coli isolates and 82 S.agalactiae isolates were determined by disk diffusion,Congo red agar and crystal violet staining,respectively.In addition,Chi-square test was used to analyze the relationship between biofilm formation ability and antimicrobial resistance.3.The antimicrobial susceptibility,biofilm formation and membrane permeability of 2 S.aureus strains(JN5 and 84184)were measured by disk diffusion,E-test method,crystal violet staining and flow cytometry,respectively.Results1.The detection rate of Escherichia coli was the highest,which accounted for 34.5% of the isolated strains.Followed by Streptococcus agalactiae and Staphylococcus aureus,the infection rates were 23% and 11.8%,respectively.2.The 123 E.coli strains were high resistant to penicillin,erythromycin,ampicillin,the resistance rates reached more than 50%.However,the isolates were relatively susceptible to ciprofloxacin and vancomycin.74.8% of strains could form a biofilm,of which more than 73.2% of the strains had the ability to form a moderate biofilm.In addition,the biofilm formation was significantly related to strain antibiotical resistant phenotype of penicillin,ampicillin,ofloxacin,erythromycin,tetracycline,chloramphenicol,ciprofloxacin and kanamycin(P<0.05).Biofilm positive strains had higher antimicrobial resistant than those biofilm negative strains.3.The 82 S.agalactiae strains were high resistant to kanamycin,the resistance rates were 97.6%.The strains were general resistant to ampicillin,erythromycin,tetracycline,ciprofloxacin and penicillin.However,the isolates were relatively susceptible to ofloxacin,chloramphenicol and vancomycin.78.0% of the S.agalactiae strains could form a biofilm,of which more than 74.3% of the strains had the ability to form a moderate biofilm.In addition,the biofilm formation was significantly related to strain antimicrobial resistant phenotype of penicillin,ampicillin,ofloxacin,erythromycin,tetracycline,ciprofloxacin and kanamycin(P<0.05).The strains that resistant to antibiotics were completely produced biofilm.4.The 42 S.aureus strains were serious resistant to penicillin,ofloxacin and ampicillin,the resistance rates were over 69%.However,the strains were relatively susceptible to chloramphenicol and vancomycin.In addition,we found that the farnesol could promote the strains antimicrobial susceptibility to penicillin,ampicillin,kanamycin,tetracycline,vancomycin,ciprofloxacin and chloramphenicol.It could inhibit the biofilm formation ability.And with the increase of farnesol concentration(0-100 ?M),the minimum inhibitory concentration of these antibiotics were decreased,biofilm formation ability was weaked and membrane permeability was increased.Conclusions1.E.coli was highly resistant to penicillin,erythromycin and ampicillin;S.agalactiae was severely resistant to kanamycin;S.aureus was highly resistant to penicillin,ofloxacin and ampicillin.In the prevention and treatment of bovine mastitis,we should make a diagnosis before taking the antibiotics so as to select suitable antibiotics.2.The biofilm formation ability of E.coli and S.agalactiae were stronger,and the antibiotical resistant phenotype of the strains were related to the biofilm formation.3.With the increase of farnesol concentration,the antimicrobial susceptibility of S.aureus were enhanced,biofilm formation ability was weaked and membrane permeability was increased.When using antibiotics to treat bacterial infectious diseases,we could cooperate with farnesol to enhance the sensitivity of the strains to antibiotics and improve the therapeutic effect.