Antigenic heterogeneity of haemagglutination type VI fimbriae produced by Escherichia coli isolated from patients with bacteremia.

In previous work it was observed that the majority of Escherichia coli strains isolated from the blood of bacteremia patients possess fimbriae which mediate mannose-resistant hemagglutination (HA) of human and monkey erythrocytes; this HA pattern (HA type VI) is different from those of enterotoxigenic E. coli possessing the colonization factor antigen CFA/I or CFA/II, which are also mannose-resistant HA positive. We and other investigators have found that HA type VI fimbriae may function as colonization factor antigens, especially in urinary tract infections. The work reported here was concerned with determining the number of antigenic types of fimbriae responsible for the HA type VI property. Fimbriae were isolated by hydrophobic interaction chromatography from four isolates of E. coli possessing the same HA pattern but belonging to different serotypes; antifimbrial antiserum was prepared by hyperimmunization of rabbits. Homologous and heterologous antifimbrial antibody titers were determined by the indirect enzyme-linked immunosorbent assay, bacterial agglutination by the tube method, and the HA inhibition test. Antiserum against the fimbriae of strain LY-71 (O4:H1) produced a high homologous titer but low or insignificant titers with fimbriae of strains LY-63 (O6:H31), LY-154 (O25:H(-)) and LY-156 (O2:H(-)). Antiserum against the fimbriae of strain LY-63 produced high titers with its own and with LY-71 fimbriae but insignificant titers with the fimbriae of strains LY-154 and LY-156. LY-154 and LY-156 fimbriae were highly cross-identical but antigenically different from those of LY-63 and LY-71. Twenty-five other test strains all identified with at least one of the prototype strains, as determined by HA inhibition tests performed with the four antifimbrial sera, although these belonged to a wide variety of serotypes. These data indicate the existence of at least two major different antigenic types of HA type VI fimbriae and possibly three, depending on the nature of the unidirectional crossidentity observed between the fimbriae of strains LY-63 and LY-71.