| Avian pathogenic E. coli (APEC) strains can cause a wide variety of extraintestinal diseases, such as avian colibacillosis in poultry, a disease characterized by cellulitis, salpingitis, septicemia, omphalitis, synovitis, osteomyelitis, swollen head syndrome, and so on. APEC are responsible for significant morbidity and mortality, which has caused considerable economic losses in different farms in many parts of the world.In order to monitor the prevalence and incidence of avian colibacillosis, we have isolated and identificated avian pathogenic E. coli (APEC) strains in large-scale farms and small farms that had shown different symptoms of E. coli infections in broiler in Jiangsu Province including Nantong, Yancheng, Changzhou, and Qingdao in Shandong Province from January 2013 to December 2014. And most of E. coli isolates were collected from heart-blood, liver, or lung of chickens with lesions of colibacillosis.During the years 2013 and 2014, a total of 203 E. coli isolates had been isolated from broilers, varying from 1-day to 32-day-old in different farms of Jiangsu Province and Shandong Province in China. Most of strains were isolated from Nantong and Qingdao (Nantong 96 isolates, Qingdao 97 isolates and the other regions 10 isolates). The determination of O antigens using commercial antisera, was carried out by agglutination and tube agglutination assay. We detected O antigens of 159 strains, and 44 strains could not be identified with the agglutination.Lots of serogroups were identified, and serogroups 078,045,01,0142,065,024,0161, were the most frequent, representing about 63.5% of the total number of detected 0 serogroups. But the O serotype distribution was different in different parts. The main serogroups were 078, 045,0142,065,024,0161,024, representing 75% of the total number of detected 0 serogroups in Nantong region, while in Qingdao,46.6% serogroups were 078,01,018,0161. In other regions, the main serogroups were 078, too. Serotype 078 was the most frequently in differen place, which might be the main pathogen of avian colibacillosis.A total of 100 strains were classified into the phylogenetic typing by PCR. We found that the phylogenetic groups A, B1, B2, D were 30%,31%,2%,37%, respectively. We also examined the isolates for the prevalence of the virulence-associated genes by PCR, which contained Iss, iroN, tsh, cvaC, iutA, irp-2, and the prevalence of virulence-associated genes were 93.5%,73.1%, 30.4%,37.2%,88.5%,34.6%, respectively, the same test had been reported in different parts of the world. In order to determine the virulence of the isolates,46 isolates were detected by using a test of lethality for 1-day-old chicks (with 107CFU). And the result was that 63% of isolates killed more than the half of the total chicks. And it implied that most of isolates (63%) were the high virulent.The most frequent O serotype was O78 in our investigation. In order to study the pathogenicity mechanism of different virulent strains belonging to the same 078 serogroup, we selected two isolates (APEC/QD/04 isolate and APEC/HA/01 isolate from different Provinces) characterized by phylogenetic typing, Pulsed Field Gel Electrophoresis (PFGE), LD50, the body dynamic distribution in 35-day-old SPF chicken and broilers. We found that APEC/HA/01 isolate was higher than APEC/QD/04 isolate in virulence. The virulence-associated gene test showed that APEC/HA/01 isolate harbored the virulence-associated genes Iss, iroN, iutA, tsh, cvaC, irp-2, while APEC/QD/04 isolate did not harbored tsh, cvaC, irp-2. The genes tsh, cvaC, irp-2 may be a reason that cause difference in virulence between them. The mechanism of APEC is more complex, there are many reasons influence the virulence of the strains, and a lot of other virulence-associated genes could be found in the future. And the two strains can be used as reference strains with different virulence. |
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