Antigenic determinants analysis and detection of virulence factors in F18 fimbriae Escherichia coli strains isolated from pigs

Abstract:

Abstract:［Objective］We determined the present distribution of serogroups and virulence factors among F18 Escherichia coli isolates from pigs with diarrhea and/or edema disease during 1998 to 2006．Epitope of F18 fimbriae was also analyzed．［Methods］A total of 75 E.coli isolates harbored fedA gene coding the major subunit of F18 fimbriae were identified by biochemical procedures and serological techniques． PCR was used to detect the virulence-related genes．An indirect ELISA was also used to analyze the antigen patterns of 33 F18 bearing E．coli strains． ［Results］Among these 75 isolates，62 were determined to be placed in total 8 serogroups，and O107 and O139 were main serogroups (61.3%) of fedA-positive isolates．The percentage of the detection of the estI，estII，elt，stx-2e，astA，orfA，irp2，fyuA，ler and eaeA among 75 strains was 64.0%，46.7%，28.0%，62.7%，26.7%，9.3%，9.3%，9.3%，1.3% and 1.3%，respectively．of the 75 strains 19 were positive for stx-2e gene only，and 20 for estI/estII/stx-2e．The 11 MAbs against F18“a”，“b”and“c”had been used in indirect ELISA to detect F18 pili antigen，44.0% (33 /75) of these isolates were F18 + when cultured in TSB cultures．Among 33 isolates expressed F18 fimbriae，21 isolates were identified as the “ac”variant，2 were identified as the“ab”variant and 10 reacted only with F18“a”specific MAbs while not with F18“b”，“c”specific MAbs． The results also revealed that the 11 MAbs recognized at least 6 epitopes including at least three common typespecific antigenic determinants“a”and two“b”antigen determinants and one“c”antigen determinant.［Conclusion］The antigenic variants of F18 fimbriae are biologically distinct．F18ab fimbriae are expressed poorly in vitro，while F18ac are more efficiently expressed in vitro and most often are linked with enterotoxin (STa and/or STb) production and serogroups O107．Some F18 fimbrial antigens experienced some variations comparing with those of F18ab and F18ac strains.