Comparison of Escherichia coli fimbrial antigen F7 with type 1 fimbriae

Two Escherichia coli O6:K2:H1 strains, C1212 and C1214, isolated from urinary tract infections, were compared for their capacity to adhere to various cells. After growth on solid medium, only C1212 bacteria agglutinate human erythrocytes and attach to urinary epithelial cells. Both of these reactions are mannose resistant. In contrast, C1214 bacteria cause a mannose-sensitive agglutination of guinea pig erythrocytes, show a mannose-sensitive attachment to buccal epithelial cells, and attach to urinary mucus. Immunoelectron microscopy revealed that C1214 bacteria possess type 1 fimbriae (mannose sensitive), which are not present in C1212 bacteria when this strain is grown on solid medium. The fimbriae of C1212 (mannose resistant) were also demonstrated by immunoelectron microscopy. We call these fimbriae demonstrated in C1212 the E. coli F7 antigen. Urinary mucus, and probably mucous material elsewhere, may function as a trap for Enterobacteriaceae with type 1 fimbriae by the specific adherence of such bacteria. We consider this a nonimmune resistance mechanism against disease caused by Enterobacteriaceae.