| Bacterial diarrhoea is a common disease on dairy goat farms.The traditional treatment for bacterial diarrhoea is mainly antibiotic therapy,which,due to the long-term overdose and unregulated use of antibiotics on farms,has resulted in increasing drug resistance in pathogenic bacteria,increasing the frequency of expression of drug-resistant genes and,more seriously,the transfer of drug-resistant genes between the bacteria,the environment and humans,posing a serious threat to human health and the ecological environment.Therefore,the reduction of antibiotics in livestock and poultry farming or the development and application of new antibiotic alternatives is currently an effective means to address the problem of antibiotic resistance.Antimicrobial peptides have unique bactericidal mechanism,not easy to produce drug resistance,and have the advantages of high efficiency,broadspectrum,no residue,improve the immunity of the body,etc.The use of antimicrobial peptides as an alternative to antibiotics for livestock breeding can help the healthy and sustainable development of animal husbandry.In order to investigate the main pathogenic bacteria causing diarrhoea in dairy goats and their drug resistance,the present study collected diarrhoeal faecal samples from some dairy goat farms in a county of Shaanxi Province,and conducted bacterial isolation and identification,and analysed the drug resistance of the main pathogenic bacteria,so as to grasp the degree of drug resistance of the main pathogenic bacteria and their carrying resistance genes,and also conducted in vitro inhibition tests using new antibiotic substitutes for antibacterial peptides,so as to provide reference for the prevention and treatment of diarrhoeal diseases in dairy goat farms in a county.The following experimental results were obtained:1.A total of 13 species and 127 strains of bacteria were identified from 83 collected dairy goat diarrhea fecal samples by bacterial isolation,purification culture and molecular biology identification,including 62 strains of E.coli(48.83%),34 strains of S.aureus(26.78%),3strains of Salmonella(2.37%),1 strain of Shigella(0.79%),2 strains of Klebsiella pneumoniae(1.56%),3 strains of Bacillus cereus(2.37%),2 strains of S.saprophyticus(1.56%),4 strains of Bacillus immobilis(3.15%),5 strains of Proteus saprophyticus(3.94%),7 strains of Enterococcus(5.51%),2 strains of Trichomonas pneumoniae(1.56%),1 strain ofAcinetobacter(0.79%),and 1 strain of Cronobacter sakazakii(0.79%),thus showing that E.coli and S.aureus were the main pathogens causing diarrhea in dairy goats in a county.2.For the 62 E.coli and 34 S.aureus strains isolated,16 and 15 different virulence genes were detected,respectively.10 virulence genes were detected for both pathogenic bacteria.fim C and fim H virulence genes of E.coli were detected at 77.42% and 100%,respectively.eae A,hly A,irp2,chu A,ompT,iss,fyu A and cvca detection rates all ranged from 9.68% to25.81%.The detection rates of virulence genes Coa and luk ED of S.aureus were 100% and64.71%,respectively,and the detection rates of Hlb,clfA,fnb A,Hla,clfA,tst,ica AD and nuc were between 11.76% and 47.06%,indicating that the 62 E.coli and 34 S.aureus strains isolated were pathogenic.3.The drug sensitivity tests were conducted on 62 strains of E.coli and 34 strains of S.aureus isolated from 8 categories and 14 antibiotics,the results showed that the resistance rates of E.coli to penicillin G reached 100%,to clindamycin,erythromycin,clarithromycin,gentamicin,kanamycin and streptomycin were higher than 58.07%,to ampicillin,cefotaxime,tetracycline,ciprofloxacin,ofloxacin,chloramphenicol and cotrimoxazole were between 9.03%and 45.16%,and E.coli multi-drug resistance up to 96.77%;S.aureus was completely resistant to penicillin and ampicillin,64.71% to streptomycin,2.94% to 41.18% to cefotaxime,gentamicin,kanamycin,tetracycline,ofloxacin,clindamycin,erythromycin,clarithromycin and cotrimoxazole,and S.aureus multi-drug resistance up to 70.59%,indicating that both E.coli and S.aureus exhibited severe multi-drug resistance.4.The 62 strains of E.coli and 34 strains of S.aureus isolated were tested for 13 drug resistance genes in 7 categories,and a total of 11 drug resistance genes were detected in E.coli,in which the detection rates of tetA,aadA,bla TEM,and Aac(3)-IV were 41.94%,25.81%,27.59%,and 22.58%,respectively,and the detection rates of gylA,cmlA,sul1,ermB,mecA,grlA,Cat1 were detected between 3.23% and 12.9%,and the multi-drug resistance gene carriage rate of E.coli was 40.32%;A total of 8 drug resistance genes were detected in S.aureus,among which gylA and grlA were detected in 88.24% and 47.06%,respectively.bla Z,bla TEM,aad A,tet M,tet A and sul1 were detected in 5.88%-17.65%,and the multi-drug resistance gene carriage rate of S.aureus was 58.82%.Both E.coli and S.aureus showed diversity and complexity in their drug resistance gene profiles.5.By agar diffusion inhibition test,microdilution method and plate coating method,it was found that the compound nano antimicrobial peptide inhibited pathogenic E.coli with a circle diameter for 27 mm,minimum inhibitory concentration(MIC)for 6.4 mg/m L and minimum bactericidal concentration(MBC)for 7.5 mg/m L;The diameter of inhibition circle for S.aureus was 30 mm,MIC was 4.0 mg/m L and MBC was 5.0 mg/m L,so the compound nano antibacterial peptide had excellent inhibition and bactericidal effect on the isolated E.coli and S.aureus.In summary,pathogenic E coli and S aureus are the main pathogens causing diarrhea in dairy goats in a county of Shaanxi Province;both pathogens showed different degrees of resistance to commonly used antibiotics,and multi-drug resistance was serious;through in vitro antibacterial experiments,it was found that the compound nano antibacterial peptide showed excellent bactericidal effect on pathogenic E.coli and S.aureus. |
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