Isolation And Identification Of Avian Pathogenic Escherichia Coli And The Correlation Of APEC Virulence Genes With Its Pathogenicity

240avian Escherichia coli isolates derived from diseased birds originated from some regions in Jiangsu and Shangdong Province were isolated and identified by standard biochemical procedures. Among these E. coli isolates,188were placed in determined serogroups,52were unserogroupable. These isolates distributed in39serogroups and64.89%(122/188) belonged to5O serogroups:024,078,088,065,086. Therefore they were predominant serogroups. We found that avian Escherichia coli serotypes were very complicated, different common O serogroups were found in different areas mentioned above. The predominant serogroups were024,086,022,088,091; and024,078,088,065in Changzhou;024,078,065in Taizhou,024,013in Jiaodong district respectively. The isolates were collected in2011-2014, and024was the most common serotype in the areas. The serotype has rarely been reported in the past, should be emphasised.The relative pathogenicity of49Escherichia coli isolates with predominant serogroups from different regions was evaluated in specific-pathogen-free1-day-old chickens. Six birds per isolate were inoculated intratracheally with0.1ml of a24-hour Luria-Bertani (LB) broth culture containing107colony-forming units (CFU) of E. coli. Based on mortality and lesions examined during a7-day postinoculation period,61.22%,18.37%and20.41%of these isolates were characterized as high, intermediate and low pathogenicity respectively. And the pathogenicity of16predominant serogroups isolates was also evaluated by the same way in susceptible1-day-old chickens,68.75%,25%and6.25%of these isolates were characterized as high, intermediate and low pathogenicity respectively, both high and moderate pathogenicity reached to93.75%. The pathogenicity of the33uncommon O serogroup isolates with both high and moderate pathogenicity is70.00%. These results suggested that almost all the tested Escherichia coli isolates were pathogenic, in which more than80%were highly and intermediately pathogenic.154avian pathogenic Escherichia coli (APEC) isolates were selected and tested for their sensitivity and resistance to15kinds of antibiotics. The result showed that these isolates were multiple-drug-resistant, and the drug resistance rate of all tested strains was exceed50%, especially, for ampicillin, doxycycline, cephalosporins, chloramphenicol, tetracycline and sulfamethoxazole, all their resistance rates were more than80%. The multi-resistance strains were very popular.69.48%of the isolates (107strains) were resistant to more than10kinds of tested antibiotics. The results indicated that the antibiotics should be used accordingly to prevent or treat the avian colibacillosis and other bacterial diseases.The phylogenetic groups of APEC isolates belong to A, B1, B2and D. In240APEC isolates, B2and D phylogenetic groups were the most common, accounting for16.25%of the isolates and33.33%, respectively, and A and B1phylogenetic groups summing up to25.84%and24.58%, respectively. B2and D accounted for49.58%of the240APEC strains. In this study, APEC isolates were detected for32virulence genes by polymerase chain reaction (PCR), in which feoB was positive for97.60%of tested isolates, sitA was95.81%, and more than50%of the isolates habored more than one out of Iss, iroN、traT、iucC、iucD、iutA、fimH genes. Less than10%of the isolates habored papA、papC、papG allele Ⅰ、papG allele Ⅲ、fela、sfa、sfaS、 afa、ibeA、cdtB、ace26genes. In this study, the prevalence of seven virulence genes iucC, iucD, iutA, tsh, iron, irp-2, iss and cvaC in highly pathogenic strains was significantly higher than that of the low pathogenic strains (P<0.05), suggesting that these virulence genes should be correlated with pathogenicity of these APEC isolates. The correlation of virulence genes with pathogenicity of isolates was postulated that an isolate was considered to be pathogenic if it habored more than two of iutA, iss, tsh, iroN, irp-2and cvaC genes. The accuracy for this hypotheise was89.74%, while the error was7.90%. Based on this correlation, the number of birds used in lethality assay of APEC isolates will be reduced and the animal welfare will be improved.