Biological Characteristics Of Escherichia Coli Associated With Neonatal Diarrhea In Piglets In Part Of China

Escherichia coli is a major cause of neonatal diarrhea (ND) in pigs. The purpose of this study was to determine the present distribution of biological characters among pathogenic Escherichia coli isolates collected from diarrheal piglets from 10 provinces in eastern China. 1 073 strains were identified with Escherichia coli isolates in 10 biochemical reactions. Among 1073 E.coli isolates associated with newborn diarrheal piglets, serogroups of 730 strains were determined while 270 were unable to be classified as certain groups, and 73 were self-agglutinated. These isolates distributed in 107 serogroups and 57.4% (419/730) out of which belonging to 11 O-serogroups: O101,O107,O20,O149,O9,O93,O23,O8,O91,O1 and O11, they were principal O serogroups in this study. Several uncommon O serogroups were discovered in this study.Multiplex-PCR was used to determine the following genes enconding four kinds of toxins of E.coli: STa,STb,LT and Stx-2e. Among the 1 073 isolates,122 isolates (11.4%) were toxin gene-positive, including 24 STa, 102 STb, 38 LT and 2 Stx-2e. In addition, seven kinds of genotypes were observed, STb~+,STb~+LT~+ and STa~+ were major genotypes, including 59 strains (48.4%) contained gene for STb only, 37 strains (30.3%) contained genes for STb and LT, and 19 strains (15.6%) contained genes for STa only. Four isolates with toxin genes were active in the rabbit intestinal-loop assays or in the weaned-pig intestinal-loop assay, and one isolate without any toxin genes was inactive in these two assays. Among 122 toxin gene-positive isolates, 120 were classified as enterotoxigenic Escherichia coli (ETEC), 1 isolate as Verotoxin-producing Escherichia coli (VTEC) and 1 isolate as VTEC/ETEC. These results suggest that ETEC was more frequently associated with neonatal diarrhea in pigs, while VTEC and VTEC/ETEC were relatively unfrequently associated with diarrhea in some regions of China.Fimbrial antigens of F4,F5,F6,F18 and F41 in the 1 073 of E.coli isolates were detected. 152 of these strains (14.2%) carried one or more fimbrial adhesins, 111 strains expressed single type of fimbriae, while 41 strains coexpressed two or more types of fimbriae. 55 of 152 strains were positive for F4, and 48 for F5, 45 for F6, 7 for F18, 47 for F41, respectively. Among 152 strains, fourteen kinds of phenotype were observed, including 44 expressed F4, and 34 for F6, 21 for F5/F41, 15 for F5, 13 for F41, which were more frequently observed in this study.In this study, among 122 enterotoxin genes positive E.coli isolates, O149,O107,O91,O93 and O11 were principal O serogroups, STb-positive isolates distributed in 24 serogroups and O107,O11,O98 and O15 were theirb principal O serogroups. And O149 was found in 89.2% of STb~+LT~+ isolates. 152 fimbrial isolates were distributed in 37 serotypes and O149, O107, O101, O11, O9 and O93 were predominant O serogroups. When all of the various kinds of enterotoxin gene-positive and fimbriae-expression strains were considerd together, there were 80 isolates encoded enterotoxin gene(s) and fimbriae, STb~+LT~+/F4~+,STb~+/F5~+F41~+,STb~+/F4~+,STb~+/F5~+ and STb~+/F6~+ were common six types in total 19 combinations. It is found that 27 isolates bearing STb~+LT~+/F4~+ belonged to serogroup O149, O149 is often associated with E.coli strains of STbLT genes-positive and F4-producting from piglets with diarrhea in some regions of China.To investigate the distribution of high pathogenicity island(HPI) of Yersinia enterocolitica and locus of enterocyte effacement pathogenicity island(LEE) in E.coli from piglets with neonatal diarrhea, 1 073 E.coli isolates were collected for detection of genes ler,eaeA,irp2 and fyuA by a multiplex-PCR. Among these E.coli isolates, 16.4%(176/1 073)of isolates possessed the genes of irp2 and fyuA, 176 isolates were distributed in 31 serogroups and O101,O23,O107,O91,O20,O8,O118,O11 and O38 were the predominant serogroups. 2.7%(29/1 073)of isolates had the genes ler and eaeA. 10 of 1 073 isolates were 4 genes-positive,7 for O91,1 for O139,1 for O38 and 1 for NT. 48.3%(14/29)of LEE~+ E. coli isolates were STa-positive and fimbriae-negative, 5 for O91,3 for O107,1 for O9,1 for O4,1 for O111,2 for NT and 1 for self-agglutinated. These results showed HPI or LEE or HPI~+LEE were detected in E.coli isolates from diarrheic piglets, and their association with pathogenicity needed further research.