Amino acid residue Ala-62 in the FimH fimbrial adhesin is critical for theadhesiveness of meningitis-associated Escherichia coli to collagens

Adhesion of meningitis-associated Escherichia coil O18acK1H7 to collagens w as characterized. The E. coli strain IHE 3034 adhered to type IV and type I collagens but not to type III collagen immobilized on glass, collagens lac k terminal mannosyl units, yet the bacterial adhesion was completely abolis hed in the presence of alpha-methyl-D-mannoside. A cat cassette was introdu ced into the fimA gene of IHE 3034, and the resulting mutant strain IHE 303 4-2 failed to adhere to collagens. In contrast, insertion of a Gm cassette into the sfaA gene of IHE 3034, encoding the S-fimbrillin, had no significa nt effect on the adhesiveness. The fim cluster from IHE 3034 was cloned and expressed in trans in the fimA::cat mutant strain IHE 3034-2. The compleme nted strain IHE 3034-2(pRPO-1) exhibited adhesiveness to type IV and type I collagens, confirming the function of the type 1 fimbria in the adhesion. We have previously shown that the type 1 fimbria from E. coli K-12 strain P C31 does not confer bacterial adhesiveness to collagens. The fimH genes fro m E. coil IHE 3034 as well as from PC31 were expressed in the fimH-null str ain MS4. The FimH from IHE 3034 potentiated collagen adherence, whereas the FimH from PC31 was inactive. Sequence comparison of fimH from IHE 3034 and PC31 revealed five amino-acid differences in the predicted mature FimH pro teins: at residues 27, 62, 70, 78 and 201. Each of these residues in the IH E 3034-FimH were individually substituted to the corresponding amino acid i n the PC31-FimH. The substitution S62-->A completely abolished collagen adh esiveness. The reverse substitution A62-->S in the PC31-FimH as well as in the FimH from another E coli strain induced collagen adhesiveness to the le vel seen with IHE 3034-FimH. Out of nine fimH genes analysed from isolates of E. coli, collagen adhesiveness as well as alanine at position 62 in FimH were found only in two O18acK1H7 isolates with the isoenzyme profile ET ty pe 1. Our results demonstrate that the amino-acid residue Ala-62 in the Fim H lectin is critical for the adhesion to collagens by a highly virulent clo nal group of E. coli.