Isolation,Identification,drug Resistance Analysis And Selection Of Drug Combination Of Swine Escherichia Coli From A Pig Farm In Guangxi

E.coli is the most common pathogen in clinical practice,often causing diarrhea and edema in piglets and threatening the health of pig herds.With the inappropriate use and long-term pressure in antibiotic treatment of E.coli disease,the problem of flora resistance is seriously complicated,developing in the direction of enhanced resistance,broader resistance spectrum and more prominent multi-drug resistance,which brings difficulties to clinical control.In this study,we collected the disease material of piglets with diarrhea from pig farms in Guigang,Guangxi,and conducted bacterial isolation and identification of suspected E.coli samples,analyzed the virulence genes,drug resistance and drug-resistance genes of the isolates,assessed the prevalence status of E.coli of clinical origin and drug resistance,and selected the combination drug regimen for multi-drug resistant strains to provide reference for clinical prevention and control.The results of the trial are as follows:1.A total of 282 environmental samples were collected from piglets with diarrhea and pig house floor troughs,and 239 E.coli strains were identified after isolation and culture,staining and microscopy,PCR and sequencing analysis.The isolates were tested for 12virulence genes,and the detection rates of fyu A,irp2 and ST genes were relatively high,48.5%,46.9%and 25.1%,respectively.2.The resistance of the isolated strains to the three antibiotics of florfenicol,tetracycline and penicillin was more serious,with the resistance rates above 90%,and the resistance rates to cefazolin,enrofloxacin,norfloxacin,cefotaxime,kanamycin and gentamicin were 72.97%,70.63%,67.57%,63.51%,45.94%and 22.97%,respectively.The isolates were sensitive to meropenem,amikacin and polymyxin E,with sensitivity rates above 90%.The resistance spectrum of isolated strains was in 2-10 species,2.70%of the strains were all resistant,and the proportion of triple drug resistance was more than 90%.The highest prevalence of relevant resistance genes in the isolates was the TEM gene,CTX-M gene forβ-lactams,and qnr S gene for quinolones,with 85.36%,74.06%and 70.71%,respectively.the most prevalent aminoglycoside antibiotic resistance gene was the ant（3’）-Ⅰa gene,carried as 63.60%.72.8%of the strains carried four or more resistance genes.The compliance rate between antibiotic resistance genes and resistance phenotypic results was92.68%for aminoglycosides,84.30%for quinolones and 97.06%forβ-lactams.3.After the isolated strain infected mice,most of the mice showed symptoms such as huddling and curling,decreased mental state,disheveled coat,slow movement,standing still,eyes closed and drowsy,standing hair trembling,and large amount of secretion in the corner of the eyes,etc.Individual mice showed diarrhea symptoms and died 12-48 hours after infection.Pathological changes in the infected mice were mainly concentrated in the abdominal cavity,the intestine was edematous and translucent with yellow contents,and the liver was bruised.Histopathological observations showed that the alveolar wall of the infected group’s lungs was thickened,alveolar interstitial and vascular stasis,and bronchial epithelial cells were necrotic and detached;renal tubular epithelial cells were hydrophobic,with loose and lightly stained cytoplasm,interstitial stasis and increased glomerular stroma;intestinal mucosa The epithelial cells were necrotic and detached,and the mucosal epithelium of the intestinal villi was separated from the lamina propria,and the lymphocytes of the lamina propria were infiltrated.Among them,many strains showed strong pathogenicity,and the LD₅₀ of F2-9 strain was 4.4×10⁷CFU.For clinical multi-drug resistant strains,the combination of enrofloxacin with amikacin,gentamicin and polymyxin E showed synergistic or additive effects on most clinical strains,and was effective in mouse protection test;the combination of florfenicol with enrofloxacin,polymyxin E,amikacin and gentamicin showed mostly unrelated effects.In this study,through the virulence gene detection and mouse infection test of the isolated enteric pathogenic E.coli strains of porcine origin,we found that the isolated strains had strong pathogenicity,and the virulence genes were mainly fyu A,irp2 and ST genes,and the analysis of drug resistance confirmed the seriousness of drug resistance of clinical strains,and the combination drug selection of drug resistant strains and validated by mouse protection test for Bacterial diarrhea prevention and control provides a reference.