Quantitative differences in adhesiveness of type 1 fimbriated Escherichia coli due to structural differences in fimH genes

Abstract

Type 1 fimbriae are heteropolymeric surface organelles responsible for the D-mannose-sensitive (MS) adhesion of Escherichia coli. We recently reported that variation of receptor specificity of type 1 fimbriae can result solely from minor alterations in the structure of the gene for the FimH adhesin subunit. To further study the relationship between allelic variation of the fimH gene and adhesive properties of type 1 fimbriae, the fimH genes from five additional strains were cloned and used to complement the FimH deletion in E. coli KB18. When the parental and recombinant strains were tested for adhesion to immobilized mannan, a wide quantitative range in the ability of bacteria to adhere was noted. The differences in adhesion do not appear to be due to differences in the levels of fimbriation or relative levels of incorporation of FimH, because these parameters were similar in low-adhesion and high-adhesion strains. The nucleotide sequence for each of the fimH genes was determined. Analysis of deduced FimH sequences allowed identification of two sequence homology groups, based on the presence of Asn-70 and Ser-78 or Ser-70 and Asn-78 residues. The consensus sequences for each group conferred very low adhesion activity, and this low-adhesion phenotype predominated among a group of 43 fecal isolates. Strains isolated from a different host niche, the urinary tract, expressed type 1 fimbriae that conferred an increased level of adhesion. The results presented here strongly suggest that the quantitative variations in MS adhesion are due primarily to structural differences in the FimH adhesin. The observed differences in MS adhesion among populations of E. coli isolated from different host niches call additional attention to the possibility that phenotypic variants of FimH may play a functional role in population dynamics.Adhesion of bacteria to mucosal surfaces is thought to play an important role in both normal ecologic and pathogenic processes (4, 12). Type 1 fimbriae (9) or pili (6, 7) are the most common adhesive organelles expressed by Escherichia coli and other enterobacteria. The only known function of these structures is that they are responsible for the D-mannose-sensitive (MS) adhesion of E. coli to cells (31-34). Type 1 fimbriae are composed primarily of the structural subunit, FimA, and minor amounts of at least three ancillary subunits, FimF, FimG, and FimH (16,19,20,35). The 30-kDa FimH subunit represents the MS adhesin (2, 13-15, 17, 20, 21, 26, 30, 42, 45).We have recently shown that allelic variants of the highly conserved fimH gene (3) encode FimH subunits that confer distinct functional phenotypes (42). We proposed using the designations M, MF, and MFP phenotypes to distinguish strains that bound to yeast mannan (MN); to both MN and human plasma fibronectin (FN); or to MN, FN, and synthetic peptides, respectively (42). The present report extends our previous studies to show that FimH subunits are also capable of conferring broad quantitative differences in the ability of type 1 fimbriated strains ...

Positive selection identifies an in vivo role for FimH during urinary tract infection in addition to mannose binding

“…This association suggests that they may be important for UTI, yet they are not under positive selection and their mutation results in no measurable in vivo effects. In the absence of any phenotypic impact in this and previous studies of polymorphism in residues 70 and 78 (37), it is possible that their association with some UPEC strains is due to nonselective processes such as neutral drift (49) or population subdivision (50). None of the PSAA was located near the conserved mannose-binding pocket of FimH, and examination of the crystal structure of the FimC-FimH-mannose complex revealed no obvious relationship between PSAA mutations and mannose binding.…”

“…Previous studies showed that mutations in PSAA residues 27, 62, and 66 can alter mannose-binding affinity, whereas changes in non-PSAA residues 70 or 78 or PSAA residue 163 had no effect on this activity (31,36,37). An A27V mutation in FimH was associated with higher lethality in an i.p.…”

“…S5). In addition, UPEC strains tend to bind mannose more avidly than fecal E. coli isolates (37), and a fimH allele encoding a protein that binds to mannose more avidly has higher fitness in a mouse model of UTI compared to an allele producing a FimH variant with weaker mannose binding activity (1,31). Mannose binding is increased by shear forces caused by urine flow, facilitating colonization in the urinary tract (36).…”

Adaptive mutations in the signal peptide of the type 1 fimbrial adhesin of uropathogenic Escherichia coli

“…Indeed, fimH alleles with SP mutations appear to circulate only for a short time from an evolutionary perspective, as they do not accumulate silent changes. In this respect, the mutant SP alleles are similar to mutant mature protein alleles that enhance FimH's ability to bind at low shear conditions and are also selected in uropathogenic E. coli (23,33). A tradeoff of mature protein mutations could be a reduced resistance to adhesion inhibition by salivary proteins in the course of oropharyngeal colonization as a part of the fecal-oral transmission of E. coli (16).…”

“…Strain CC191pJDT3 has pJDT3 without the fimH signal sequence. For the morphology, adhesion, and neutrophil studies we used strains based on fimH-null UTI isolate CI10-9 (16) with pPKL9, which contains the positive type 1 fimbrial regulator, FimB (33). fimH alleles, all with the same mature protein coding sequence and different signal sequences, were introduced into CI10-9 on pBeloBAC11 (New England Biolabs), generating strains LS76 (WT FimH SP), LS60 (T-6N), LS68 (T-6N/V-10I), LS154 (T-6N/ V-10A), and LS141 (V-4E).…”