Isolation Identification And Drug Resistance Analysis Of Pathogenic Escherichia Coli From Lung Of Newborn Calves

Bovine parenteral pathogenic Escherichia coli(Expec)is a kind of pathogenic bacteria that can cause parenteral tissue infection,which can cause sepsis,meningitis,urinary tract infection and pneumonia in cattle,and easily cause secondary or mixed infection.In this study,pathological observation and sampling were conducted on the pathological tissue of calves suspected to be caused by Escherichia coli in a cattle farm in Alar.Through bacterial isolation,morphological,physiological and biochemical identification,and16 S r RNA identification,the pathogen was confirmed as bovine lung derived Expec.The harm and pathological manifestations of this pathogen were studied by animal experiments.The virulence gene and drug sensitivity test of the isolated bovine lung Expec strains were carried out in order to provide reference for the prevention and treatment of bovine Expec infectionFrom July to November 2020,newborn calf tissues(spleen,heart,lymph node,liver,kidney,lung)that died of respiratory diseases were collected from a large-scale cattle farm in Alar.There were obvious bleeding points and congestion points in lung and heart crown fat of dead calves.After bacterial isolation and biochemical identification,it was preliminarily identified as Escherichia coli.By bacterial 16 S r RNA gene identification,the genetic sequence of the isolated strain was more than 99% similar to that of E.coli reference strain,and it was identified as parenteral pathogenic Escherichia coliThe virulence gene of the isolated bovine Expec strains was detected by PCR amplification method.The results showed that 15 strains of agg R virulence gene were amplified from the 12 virulence genes,and13 strains of ipa H,12 strains of hly F,10 strains of fim C,9 strains of fyu A and 7 strains of irp2 were amplified,respectively.The detection rates of virulence genes were agg R(65.21%),ipa H(56.52%),hly F(52.17%),fim C(43.47%),fyu A(39.13%)and irp2(30.43%),among which agg R and ipa H had the highest amplification rates.The isolated bovine Expec strain was used in the challenge test of mice.The results showed that 6 experimental groups of mice died successively within 12?36h.The bacteria isolated from the lung tissues of dead mice were identified as ExpecThe 30 bovine Expec strains screened in this study were tested for antibiotic susceptibility,the result shows: ?-lactams,quinolone,aminoglycoside and tetracycline drugs resistant rate is higher,the penicillin(95.65%),ampicillin(91.3%),gentamicin(82.6%),kanamycin(78.26%),Oxacillin(78.26%),vancomycin(73.91%),The drug resistance rate was high.The detection rate of ?-lactam bla TEM and quinolone gyr A resistant genes was the highest.,which were 65.21% and 52.17%,respectively.The detection rate of aminoglycoside resistance gene aac C2 was 39.13%.The sulfonamides resistance gene sul2 and tetracycline tet(A)resistance rates were the same.In this study,through the isolation and identification,drug resistance analysis,drug resistance gene and virulence gene detection and animal test of calf source Expec in a large-scale cattle farm in Alar,the pathogen and drug resistance were determined,which provided a theoretical basis for the diagnosis and control of cattle source Expec in this area.