| Escherichia coli,one of the most common bacteria and pathogens,is an important component of the microbiota in all regions of the world and can cause infections in humans and animals through a variety of routes under certain conditions,posing a public health concern.E.coli pathogens can colonise the respiratory,intestinal and reproductive tracts,and pathogenic E.coli can attack or damage the host in the process of colonisation,leading to a variety of livestock,poultry and human pathogens and different types of pathogenesis,resulting in different types of E.coli disease,mainly including porcine E.coli,bovine E.coli and avian E.coli.Infections can occur at all ages and in all seasons,causing serious economic losses to the farming industry.Systematic studies on E.coli have been reported around the world,but there is little information on systematic studies in southwest China,especially on duck-derived E.coli disease.The hot weather and high humidity in the southwest are ideal for the growth of E.coli,and the long history of duck farming in the southwest has often led to reports of largescale E.coli epidemics on duck farms.To investigate the molecular epidemiological characteristics of pathogenic E.coli in ducks in southwest China and to provide a basis for prevention and control strategies of pathogenic E.coli in southwest China,a large number of bacterial isolates were isolated from duck farms in Rongchang District,Dazu District and Longchang City during 2014-2021 in this study,which were further characterized by 16 sr DNA,PHO-A gene and biochemical tests,and studied for their typing characteristics and virulence The results of the study are as follows.The results of the analysis are as follows.1.0 Identification of isolatesA large number of bacterial isolates were isolated from the heart,liver,spleen and plasma membrane of dead ducks in Rongchang District,Dazu District and Longchang City during2014-2021.5 strains,and 20 strains from Longchang City.2.0 Typing resultsIn this study,107 E.coli isolates from Rongchang District,Dazu District and Longchang City were systematically analysed by sugar fermentation typing test,16 sr DNA sequence construction,evolutionary tree and genetic structure stacking map,O-antigen serotyping by wzx/wzy gene and ERIC-PCR genotyping.The sugar fermentation typing test was based on its ability to break down monosaccharides,disaccharides and polysaccharides into three clusters,B1(51%),B2(41%)and B3(8%);the evolutionary tree was divided into three clusters,cluster Ⅰ(98%),cluster Ⅱ and clusterⅢ,and within cluster Ⅰ into four sub-clusters,A,B,C and D.The main epidemic causing isolates during 2014-2021 were The isolates that mainly caused epidemic infection during 2014-2021 wereⅠ A and Ⅰ B,2014-2017 were Ⅰ A,2017-2020 were Ⅰ B,2020-2021 were Ⅰ A and Ⅰ B.The genetic structure stacking map was divided into six major clusters,namely A 3%,B 66%,C 7%,D 4%,E 18% and F 2%,in which more than 42% of the isolates contained two or more genetic structures,and the genetic structure of the isolates was determined by comparison with The evolutionary direction of E.coli in Rongchang,Dazu and Longchang bordering the three regions was inferred from a comparison with the 16 sr DNA evolutionary tree phenotypes,and the evolutionary direction of multiple E.coli groups may be genetically cross-spread.serotype fusion types(O78+O145 and O7+O145);ERIC-PCR genotyping identified nine genotypes in two large clusters,A(70%)and B(30%),with both the 16 sr DNA phenotype and the O antigen serotype being biased in the ERIC-PCR genotype,with 73% of the 16 sr DNA phenotype isolates clustered in the A cluster genotype,and the The dominant serotypes in the serotypes,O78,07 and O145,had more than70% of isolates clustered in cluster A genotypes as well,confirming the predominance of cluster A genotypes of E.coli in the southwest.3.0 Results of virulence gene assay,pathogenicity test results and drug sensitivity test resultsIn this study,16 virulence genes were detected in 107 pathogenic E.coli strains,and 11 virulence factors were detected.Three virulence genes(yij P 96.26%,ibe B 85.98% and omp A 100%)were detected at a rate of 85% or more,with omp A gene reaching 100% detection rate.Among these detected virulence genes,which are closely related to the adhesion,invasion and nutrient uptake of E.coli,virulence genes containing a large number of strong pathogenicity were detected: pathogenic E.coli carrying the Tsh virulence gene(25.23% detection rate);pathogenic E.coli carrying the Yersin virulence island HPI(31.78% detection rate);pathogenic E.coli carrying the est B virulence gene producing enterotoxin-producing pathogenic E.coli(31.78% detection rate);septicemia-positive pathogenic E.coli carrying the Vat virulence gene(2.8% detection rate);and pathogenic E.coli carrying the iuc A virulence gene(44.56% detection rate).The results showed that the 107 pathogenic E.coli were most sensitive to minocycline and polymyxin,most sensitive to aminoglycosides(bupropion,kanamycin,gentamicin,and The most susceptible to macrolides(methicillin and erythromycin)and clindamycin,with a resistance rate of100%,and more resistant to penicillin,benzocillin,piperacillin,carbenicillin and ampicillin(penicillins),with a resistance rate of 91%,tetracycline,doxycycline(tetracyclines),with a resistance rate of 83%,and cotrimoxazole(sulfonamides)with a resistance rate of 81%.The results of the drug sensitivity tests showed that the overall resistance of pathogenic E.coli in the three regions was severe,with 30% of pathogenic E.coli showing multi-drug resistance,and the overall trend of resistance rate of pathogenic E.coli in the three regions was increasing over time.The distribution of pathogenicity and resistance profiles combined with 16 sr DNA phenotypic analysis revealed that isolates with strong pathogenicity were also highly resistant to drugs,and combined with ERIC-PCR genotypic analysis revealed that isolates with strong pathogenicity and resistance were more inclined to cluster A of the ERIC-PCR genotype,confirming the strong pathogenicity of cluster A genotype E.coli. |
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