Cloning and characterization of a new type of fimbria (S/F1C-related fimbria) expressed by an Escherichia coli O75:K1:H7 blood culture isolate

Abstract

The Escherichia coli blood culture isolate BK658 (O75:K1:H7) expresses F1A and F1B fimbriae as well as a third fimbrial type which reacts with anti-S-fimbrial antiserum but fails to show S-specific binding properties (i.e., agglutination of bovine erythrocytes). To characterize these fimbriae, we cloned the respective genetic determinant in E. coli K-12. The resulting recombinant clone HB101(pMMP658-6) expresses fimbriae of 1.2-micron length and a diameter of approximately 7 nm. The determinant codes for the fimbrillin subunit, a protein of 17 kilodaltons in size, and for at least five other proteins of 87, 31, 23, 14.3, and 13.8 kilodaltons. By restriction analysis and by DNA-DNA hybridization, it could be shown that the cloned fimbrial determinant of strain BK658 exhibits a high degree of sequence homology to the gene clusters coding for S fimbrial adhesins (sfa) and F1C fimbriae (foc). By using the Western blot (immunoblot) technique and a quantitative enzyme-linked immunosorbent assay, it could be further demonstrated that the cloned fimbriae of BK658, S fimbriae, and F1C fimbriae share cross-reactive epitopes as well as antigenic determinants specific for each fimbrial type. No antigenic cross-reactivity with F1C fimbriae could be detected. The results indicate a genetical and serological relatedness of the cloned fimbriae to S fimbriae and F1C fimbriae. Therefore, this new type of fimbriae is preliminarily termed S/F1C-related fimbriae (Sfr).