Study On The Diversity Of Bacteria And Biological Characteristics Of Main Pathogenic Bacteria In Milk Of Cow Mastitis

Xinjiang is a large animal husbandry province in China,and the dairy industry plays an important role in Xinjiang economy.However,with the continuous expansion of Xinjiang dairy industry,the prevalence of cow mastitis has seriously restricted the development of the dairy industry and caused serious economic losses to the dairy industry.The purpose of this study is to find out the diversity of microbial community and the prevalence of main pathogenic bacteria in milk of dairy cows with mastitis in some areas of Xinjiang,and to provide reference for the prevention and control of cow mastitis.Methods: 1.The samples of clinical mastitis and healthy dairy milk were collected from two randomly selected cattle farms respectively.The 16 S r RNA gene V3-V4 region of bacteria was amplified by PCR and high-throughput sequencing.The diversity of microbial communities in clinical dairy milk samples and healthy dairy milk samples were analyzed,and the differences between them were compared.2.Milk samples of dairy cows with mastitis were randomly collected from 7 dairy farms.Staphylococcus aureus and Escherichia coli were identified by conventional methods and 16 S r DNA sequence analysis.The K-B disk diffusion method was used to detect the drug sensitivity of the isolates,then the virulence gene was detected by PCR,and the pathogenicity was detected by mouse challenge test.Result: 1.A total of 25 phyla,47 classes,82 orders,174 families and 349 genera were obtained from 6 clinical mastitis samples,and 23 phyla,38 classes,61 orders,125 families and 212 genera were obtained from 2 healthy dairy milk samples.In clinical mastitis samples,the dominant bacteria were Proteobacteria,tenerictes,Firmicutes,Bacteroidetes and actinobacteria;in healthy milk samples,the dominant bacteria were Proteobacteria,Firmicutes and Bacteroidetes.At the genus level,the dominant bacteria in healthy milk samples were less than those in mastitis samples.2.A total of 5 strains of Staphylococcus aureus and 48 strains of Escherichia coli were isolated from 142 mastitis samples.Staphylococcus aureus was detected and isolated from 2 of 7 dairy farms,with the isolation rates of 7.14%(2/28)and 8.82%(3/34)respectively.The drug sensitivity test showed that the drug resistance rates of these Staphylococcus aureus to penicillin G,ampicillin,streptomycin,ceftazidime and amoxicillin were 60%-80%,and the resistance rate to erythromycin was20%.Five major virulence genes,nuc,clfa,fnb B,eta,sea and sea,were detected.The results of mice challenge test showed that all mice in each group died,and the mortality was 60%-100%.The isolation rate of Escherichia coli was 33.8%(48/142).The results of drug sensitivity test showed that the resistance rate of Escherichia coli isolates to penicillin G was 85.4%,and the resistance rate to clindamycin,amoxicillin,ampicillin and cefazolin was more than 40%.Seven virulence genes,iuc D,Fyu A,irp2,ast A,esc V,eae A and ler,were detected in the isolates.The results of mice challenge test showed that all mice in each group died,and the mortality rate was 60%-100%.Conclusion,after suffering from mastitis,the diversity and abundance of bacteria in dairy cows increased significantly,and the distribution and abundance of bacteria in milk would change,indicating that the imbalance of bacteria is one of the characteristics of clinical mastitis.The isolation rate of Staphylococcus aureus is low,the isolation rate of Escherichia coli is high,the drug resistance of Staphylococcus aureus is not strong,many strains carry multiple virulence genes and have strong pathogenicity.Escherichia coli isolates have strong drug resistance and carry multiple virulence genes,all of which are highly pathogenic.