| Calf diarrhea is one of the major diseases that affect the growth and development of calves,which brings huge economic losses to the cattle industry.In order to analyze the main pathogens causing calf diarrhea in China,232 diarrhea calf manure and 225 serum samples collected from 30 cattle farms in Gansu,Inner Mongolia and other provinces were examined by pathogen investigation and serum antibody testing.Moreover,the dominant serotype,pathogenicity and drug resistance of major pathogenic E.coli were further studied.Preliminary screening of Tibetan herbal with antibacterial effect in this study will help establish disease prevention and control methods and develop therapeutic drugs.The main research and conclusions of this study are as follows:1.Bovine viral diarrhea virus(BVDV)and bovine rotavirus(BRV)were detected by colloidal gold technique.Bovine coronavirus(BCV)Cryptosporidium parvum and other pathogens in 232 anus swab samples were detected by ELISA.Bacterial isolation and identification method was used to identificate major pathogens.ELISA was used to detect BVDV and BRV in 225 serum samples.The results showed that the positive rates of BRV,BVDV and BCV were 44.40%,15.09% and 8.62%,respectively.In this study,455 strains of 61 species were isolated and identified.The Sep Aration rate,positive rate and mixed infection rate of E.coli,Cryptosporidium parvum and a mixture of these two pathogens were 90.52%,1.72% and 80.60%,respectively.The results of serological tests showed that positive rate of serum antibody of BRV and BVDV was 98.67% and 84.44%.2.The 83.33% in 210 isolated strains of E.coli can be determined serotype,but 16.67% was failure to determine serotypes by using E.coli O antigen polyvalent and unit price diagnosis of serum detection.The major serotypes of isolated E.coli strains were O127,O158,O44,O55,O128,O61 and O101,and their proportion were 19.23%,10.44%,8.24%,7.14%,6.59%,6.04% and 6.04%,respectively.Animal pathogenicity test showed that the proportion of pathogenic effect of isolated E.coli was 68.57%,and strong pathogenic effect accounted for 27.62%.The results of virulence gene amplification showed that the number of strains carrying F17 virulent genes was the highest,accounting for 73.81%.The detection rate of Stx1,ast A and Sep A virulence genes were over than 10%.3.The antimicrobial susceptibility of isolated E.coli to cefuroxime and carbenicillin was 83.33% and 80.00% by the KSI method.There are 96.67% in 210 isolated strains of E.coli carry quinolones gyr B and aminoglycoside str AB resistance gene.There were positive correlations between quinolones Par C,tetracycline tet A,tet B,aminoglycoside Aph(3’)-Ⅱ,chloramphenicol cml A,sulfonamid sul1 resistance genes and antibiotic resistance phenotype of the corresponding class of antibiotics(P <0.05).4.Antibacterial effect of seven kinds of single-flavor Tibetan medicine and its compound on multi-resistant E.coli was evaluated in vitro using the oxford cup method.The results showed that compound Tibetan medicine,Myrobalan,Herba dracocephali tangutici and Aconitum tanguticum have a better antibacterial efficacy.In particular,Aconitum tanguticum has a strong antibacterial effect on E.coli and the minimum inhibitory concentration(MIC)was 250 mg/m L.In summary,the major pathogens causes of calf diarrhea in these regions were BRV,BVDV and E.coli.Mixed infection was prevalent,and BRV and BVDV infection were more serious in the dairy farms.O127 and O158 were the dominant serotypes of E.coli.In addition,F17 was the most common virulence gene in isolated E.coli.Most of the isolated strains had a pathogenic effect on mice.The study found that E.coli produced a certain resistance and carried resistant genes.Moreover,some drug resistance genes were positively correlated with the corresponding drug resistance phenotype.Aconitum tanguticum has a strong antibacterial effect on E.coli. |
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