Designations F18ab and F18ac for the related fimbrial types F107, 2134P and 8813 of Escherichia coli isolated from porcine postweaning diarrhoea and from oedema disease.

The relatedness of the fimbriae produced by eight E. coli strains including type strains with F107 fimbriae, 2134P pili and colonization factor 8813 (preliminary F18), was examined. These strains had been isolated principally from pigs which were affected with postweaning diarrhoea or with oedema disease. The fimbriae were analyzed by means of electron microscopy, slide agglutination, immunofluorescence, immunogold labelling, immuno-diffusion, immunoelectrophoresis and western blot, molecular genetic techniques, and in vitro adhesion. The fimbriae of all the strains were long flexible filaments with a diameter not larger than 4.6 nm showing a zig-zag pattern. Results obtained by the serological techniques confirmed that the fimbriae possessed a common antigenic determinant designated 'a' in addition to a variant-specific determinant designated 'b' or 'c'. Immunoelectron microscopy demonstrated that the determinants 'a' and 'b' or 'a' and 'c' were localized along the same fimbrium. In immunoelectrophoresis, fimbrial extracts of selected strains yielded a single precipitation line towards the cathode. One single major subunit of approximately 15 kDa was recognised in western blots by antisera against the common antigenic determinant and the variant specific determinants. All strains possessed sequences related to gene fedA, coding for the major subunit of fimbriae F107. Two types of fedA-related subunit genes were differentiated, corresponding to the 'ab' and 'ac' types of fimbriae as defined by serological methods. The results demonstrated that F107 fimbriae, 2134P pili and colonization factor 8813 are related, and that two serological variants can be distinguished. We propose designations F18ab (for F107), and F18ac (for 2134P and 8813) in analogy to the nomenclature of F4 fimbriae.