Molecular Characteristics Of Staphylococcus From Bovine Mastitis In Gansu,Qinghai And Ningxia Province

Dairy cow mastitis has always been recognized as a worldwide problem.It not only reduces the milk yield,but also affects the quality of milk.It seriously harms the health of dairy cows,and also poses hidden dangers to public safety and human health.In this study,Staphylococcus was isolated and identified from mastitis milk samples in Northwest China.Then,the resistance phenotype to 13 drugs and 31 related resistance genes of Staphylococcus were detected.After that,the virulence genes and the biofilm formng ability of the isolates were determined.Finally the genotyping was performed using multilocus sequence typing,Staphylococcal A typing,pulsed field gel electrophoresis typing and SCCmec typing.The objective of this study was to better understand the antibiotic resistance status and dominant clones of Staphylococcus in the dairy farms in Northwest China.A total of 215 strains of Staphylococcus were isolated from 578 milk samples.Among them,65 strains were Staphylococcus aureus,39 were Staphylococcus haemolyticus 38 were Staphylococcus simulans,28 were Staphylococcus sciuri,20 were Staphylococcus saprophyticus,10 were Staphylococcus chromogenes,9 were Staphylococcus epidermidis,6 were Staphylococcus equorum.MIC values of 13 commonly used drugs to 215 Staphylococcal isolates were determined.The results showed that resistance rates of almost all Staphylococcus to erythromycin,lincomycin and kanamycin exceeded 50%.The resistance rate of Staphylococcus haemolyticus to erythromycin and lincomycin was even more than 90%.The Staphylococcus chromogenes was even worse,and the resistance rate to erythromycin and lincomycin was 100%.Staphylococcus aureus,Staphylococcus simulans,Staphylococcus sciuri and Staphylococcus saprophyticus were sensitive to vancomycin and linezolid,but were resistant to the remaining 11 antibiotics.Thirty-one resistance genes of 13 antibiotics were detected in Staphylococcus.According to the results,the resistance genotypes were generally consistent with the resistance phenotype.Most resistant strains carried at least two resistance genes.Among 65 strains of Staphylococcus aureus,the incidence of ermC,aacA-aphD,gyrA and lnuA were 81.5%,76.9%,73.8% and 73.8% respectively.The carrier rates of aadD and cfr were 63.1%.The detection rates of vga,mecA and rpoB were 7.7%,27.6% and 1.5%,respectively.Vancomycin and linezole resistance genes were not detected.Among 150 strains of coagulase negative Staphylococcus,the carrying rates of erm(B),vga,blaZ,mecA,tet(M),tet(L),tet(K),cfr,fexA,aacA-aphD,aadD,glrA,glrB and ropB genes were 52.0%,14.7%,50.0%,30.0%,8.7%,28.7%,8.0%,45.3%,14.7%,66.7%,16.7%,27.3%,28.0% and 2.7%,respectively.Staphylococcus biofilm-forming ability and related virulence genes were detected.There were 124 strains(51.6%)of staphylococcus with biofilm-forming ability.Among them,47 strains of Staphylococcus aureus(47.3%),23 strains of Staphylococcus haemolyticus(59.0%),18 strains of Staphylococcus simulans(47.3%,18/38),19 strains of Staphylococcus sciuri(50.0%),5 strains of Staphylococcus saprophyticus(25%,5/20),4 strains of Staphylococcus chromogenes(40.0%)and 8 strains of Staphylococcus epidermidis(88.9%)had biofilm forming ability.The remaining 91 strains(42.3%)of Staphylococcus had no ability to form biofilm.Of the Staphylococcus with biofilm formation ability,the virulence genes sea,luks and lukf had similar frequency in Staphylococcus with different biofilm formng abilty,virulence genes hla(93.8%)and clfA(62.5%)appeared most frequently in the Staphylococcus with weak biofilm forming ability,virulence genes clfB(74.4%)appeared more frequently in the Staphylococcus with medium biofilm forming ability,virulence genes seb(60.6%),tsst(72.7%),coa(72.7%),fnbA(100.0%),fnbB(97.0%),icaA(100.0%)and icaB(100.0%)appeared more frequently in the Staphylococcus with strong biofilm forming ability.Different methods were used for genotyping of the strains.Staphylococcus aureus strain ST15-A1-t803 was the main epidemic type in this area and belongs to CC1.SCCmec IV was the main epidemic strain of MRSA strain in this area,with 5 strains.The dominant strain of MRCNS was SCCmec ?,with 15 strains,followed by SCCmec ?.