| A total of 416 samples were collected from the tissues and feces of chicken died of Escherichia coli disease in the northeast of China from December 2005 to June 2006. 219 Escherichia coli isolates were obtained from these samples by morphology observation, routine microbiological tests, biochemical reaction and molecular diagnostic methods. Subsequently the identification of the O serotype were done.The O antiserum used in this study were provided by the Veterinary Drugs Institution of Ministry of Agriculture of China. The E. coli strains included in this study fell into 43 O groups, of which O78(19,8.68%),O138(14,6.4%) ,O2(13,5.94%) ,O141(12,5.48%),O149(9, 4.11%),O8(9,4.11%),O107(7,3.20%),O1(6,2.74%),O4(6,2.74%)together accounted for 43.38% of the 219 isolates examined. 30 isolates were not serotyped.The isolates were also examined for their susceptibility to 18 antimicrobial agents. The antimicrobial susceptibility test was completed according to the standard procedure advised by WHO.The results were compared with the result of ATCC25922 which was set as control strain. And they were also tested by PCR for the presence of resistance genes for tetracycline, streptomycin and spectinomycin and common virulence genes of pathogenic E. coli. Antimicrobial resistance frequency among E. coli isolates from chicken in the Northeast of China was more severe in comparison with other countries. Resistance profiles suggest that tetracycline may be the most resistant antimicrobial agents tested in this study. The resistant rate of tetracycline was 94.5%. The followed antimicrobial agents were norfloxacin (86.8%), chemitrim(82.2%), ampicillin (81.3%), enrofloxacin(76.8%), nalidic acid(76.2%), rifampicin(74.0%), ciprofloxacin(63.0%), kanamycin(58.4%), streptomycin(45.2%), gentamycin(35.2%), amoxicillin(32.5%), chloramphenicol(26.4%), cefalotine(18.3%), amikacin(16.5%), spectinomycin(47.9%), cephazoline(4.6%),and ceftriaxone(2.2%).Based on the marker of virulence genes and the serotyping, the E.coli. can be divide into the following five categories: enterotoxigenic E. coli (ETEC), enteroinvasive E.coli (EIEC), enteropathogenic E. coli(EPEC), enterohemorrhagic E. coli (EHEC), and enteroaggregative E. coli (EAEC). These results may have important implications with regards to the spread and persistence of resistance and virulence genes in bacterial populations and to the prudent use of antimicrobial agents.In order to detect the status of E.coli infection induced by stx1, stx2 and EAST1 in the northeast of China,we adopted eribble extract way to prepaire strains'DNA. The primers for stx1, stx2 and EAST1 were designed and composed according to the sequence published in genebank. Amplification were achieved by PCR, fragment length are 130bp, 346bp and 111bp respectively, and the product were identified by agarose gel electrophoresis.According to the results achieved from above we screened positive strains. Result :55 strains were positive for stx1(21.5%), 56 strains were positive for stx2(21.87), 103 strains were positivefor EAST1(40.23%) . Choosing 11 strains E.coli including 4 stx1 positive, 4 stx2 positive and 3 postive EAST1, chromosomal DNA was prepared according to molecular clone: A laboratory Manual.Amplification of stx1, stx2 and EAST1 were achieve by PCR with different primers.the resulted DNA fragment with expected size was cloned into vector pMD18-T and subsequently subjected to restriction enzyme and PCR reaction and sequencing.The results showed that all the sequences have over 93% homogenous to published date,. the method of PCR to detect the gene of toxicity is shortcut,sensitive and specific.
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