| Staphylococcus aureus is a common zoonotic pathogen that is widely distributed in nature.About 20%of people and animals carry Staphylococcus aureus for a long time,causing a wide variety of diseases including bacteremia,osteomyelitis,infective endocarditis and bovine mastitis,in severe cases,it may even threaten the lives of patients or infected animals.Dairy cow breeding is an important industry in Ningxia region,cow mastitis caused by Staphylococcus aureus infection has brought huge economic losses to dairy farming.This study collected dairy cow mastitis samples from multiple scale aquaculture farms in Ningxia and investigated the epidemiological characteristics of Staphylococcus aureus in cattle in Ningxia.At the same time,representative strains of Staphylococcus aureus from dairy cow in Ningxia were selected to perform whole genome sequencing analysis.The genetic evolution characteristics of the strains provide scientific basis for the prevention and control of bovine associated Staphylococcus aureus infection in Ningxia.In this study,clinical and subclinical mastitis milk samples were collected from dairy cow farms of different scales in Ningxia during 2015-2016.The separation of Staphylococcus aureus was determined by Chromogenic plate and multiplex PCR.The MIC values of the 15 antibacterial drugs were determined by the microbroth dilution method.The results showed 125(26.8%,125/466)Staphylococcus aureus strains were isolated and identified,of which 9 strains were MRSA strains(7.2%,9/125).All strains were sensitive to amikacin,linezolid,vancomycin,and daptomycin,tested strains showed different levels of resistance to the remaining 11 antimicrobial drugs.All MRSA strains were 100%resistant to ceftiofur,ampicillin,oxacillin,gentamicin,erythromycin,and clindamycin.A total of 19 resistance genes and 20 virulence genes were detected in 125 Staphylococcus aureus strains by PCR.The results showed that the carrying status of resistance genes in strains was complicated.The detection rates of blaZ,norA,gyrA,grlA,and ermC were high.The test results of virulence genes showed that the detection rate of novel enterotoxin genes(52.8%,66/125)was higher than the detection rate of classical enterotoxin genes(20%,25/125).The most common enterotoxin genotype combination is selm+selu+sei+selo+seln,which is very similar to the currently popular enterotoxin genotype combination seg+sei+selm+seln+selo+selu,two CC30 MSSA strains and two CC59 MRSA strains carry the PVL gene,while one CC 239 MRSA strain and three CC5 MSSA strains carry the TSST-1 gene.MLST,spa,and agr were performd to classify 125 Staphylococcus aureus strains in Ningxia,and nine MRSA strains were typed by PFGE,SCCmec,and dru-typing methods.The results showed that ST50 and ST97 were the prevalent clone types in Ningxia.Two new ST types(ST4053 and ST4066)were identified in this study.ST4053(27.2%,34/125)had a high isolation rate.16 spa types were identified,t224 is the prevalent clone type in the region.The main agr type was agr-II(44%,55/125)Staphylococcus aureus.The typing results showed the prevalent clone type of the MRSA strain from dairy cow in Ningxia was SCCmec Ⅲ-dt11v-ST239-t037.According to the results of spa type,16 Staphylococcus aureus strains in Ningxia were sequenced and analyzed.The results showed that the similarity of the genomic sequence of Staphylococcus aureus in Ningxia was high,and some of the strains carried multiple drug-resistance genes.The same CC strains have a more recent evolutionary relationship.In conclusion,we investigated the various genotyping,whole genome sequencing analysis and drug resistance of Staphylococcus aureus isolated from dairy cow in Ningxia.It revealed that the drug resistance situation and the molecular epidemiological characteristics of Staphylococcus aureus in Ningxia.It provides a theoretical basis for the prevention and control of Staphylococcus aureus infection and rational drug use. |
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