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

ABSTRACT: FimH, the type 1 pilus adhesin of uropathogenic Escherichia coli (UPEC), contains a receptor-binding domain with an acidic binding pocket specific for mannose. The fim operon, and thus type 1 pilus production, is under transcriptional control via phase variation of an invertible promoter element. FimH is critical during urinary tract infection for mediating colonization and invasion of the bladder epithelium and establishment of intracellular bacterial communities (IBCs). In silico analysis of FimH gene sequences from 279 E. coli strains identified specific amino acids evolving under positive selection outside of its mannose-binding pocket. Mutating two of these residues (A27V/V163A) had no effect on phase variation, pilus assembly, or mannose binding in vitro. However, compared to wild-type, this double mutant strain exhibited a 10,000-fold reduction in mouse bladder colonization 24 h after inoculation and was unable to form IBCs even though it bound normally to mannosylated receptors in the urothelium. In contrast, the single A62S mutation altered phase variation, reducing the proportion of piliated cells, reduced mannose binding 8-fold, and decreased bladder colonization 30-fold in vivo compared to wild-type. A phase-locked ON A62S mutant restored virulence to wild-type levels even though in vitro mannose binding remained impaired. Thus, positive selection analysis of FimH has separated mannose binding from in vivo fitness, suggesting that IBC formation is critical for successful infection of the mammalian bladder, providing support for more general use of in silico positive selection analysis to define the molecular underpinnings of bacterial pathogenesis.

SUBMITTER: Chen SL

PROVIDER: S-EPMC2794649 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:IntroductionRecurrent urinary tract infections (RUTIs) have a significant negative impact on quality of life and healthcare costs. To date, daily prophylactic antibiotics are the only treatment which have been shown to help prevent RUTIs. D-mannose is a type of sugar which is believed to inhibit bacterial adherence to uroepithelial cells, and is already being used by some women in an attempt to prevent RUTIs. There is currently insufficient rigorous evidence on which to base decisions about its use. The D-mannose to prevent recurrent urinary tract infections (MERIT) study will evaluate whether D-mannose is clinically and cost-effective in reducing frequency of infection and symptom burden for women presenting to UK primary care with RUTI.Methods and analysisMERIT will be a two-arm, individually randomised, double blind placebo controlled, pragmatic trial. Participants will be randomised to take D-mannose powder or placebo powder daily for 6 months. The primary outcome will be the number of medical attendances attributable to symptoms of RUTI. With 508 participants we will have 90% power to detect a 50% reduction in the chance of a further clinically suspected UTI, assuming 20% lost to follow-up. Secondary outcomes will include: number of days of moderately bad symptoms of UTI; time to next consultation; number of clinically suspected UTIs; number of microbiologically proven UTIs; number of antibiotic courses for UTI; quality of life and healthcare utilisation related to UTI. A within trial economic evaluation will be conducted to examine cost-effectiveness of D-mannose in comparison with placebo. A nested qualitative study will explore participants' experiences and perceptions of recruitment to, and participation in a study requiring a daily treatment.Ethics and disseminationEthical approval has been obtained from South West-Central Bristol Research Ethics Committee. Publication of the MERIT study is anticipated to occur in 2021.Trial registration numberISRCTN 13283516.

Project description:ImportanceRecurrent urinary tract infection (UTI) is a common debilitating condition in women, with limited prophylactic options. d-Mannose has shown promise in trials based in secondary care, but effectiveness in placebo-controlled studies and community settings has not been established.ObjectiveTo determine whether d-mannose taken for 6 months reduces the proportion of women with recurrent UTI experiencing a medically attended UTI.Design, setting, and participantsThis 2-group, double-blind randomized placebo-controlled trial took place across 99 primary care centers in the UK. Participants were recruited between March 28, 2019, and January 31, 2020, with 6 months of follow-up. Participants were female, 18 years or older, living in the community, and had evidence in their primary care record of consultations for at least 2 UTIs in the preceding 6 months or 3 UTIs in 12 months. Invitation to participate was made by their primary care center. A total of 7591 participants were approached, 830 responded, and 232 were ineligible or did not proceed to randomization. Statistical analysis was reported in December 2022.InterventionTwo grams daily of d-mannose powder or matched volume of placebo powder.Main outcomes and measuresThe primary outcome measure was the proportion of women experiencing at least 1 further episode of clinically suspected UTI for which they contacted ambulatory care within 6 months of study entry. Secondary outcomes included symptom duration, antibiotic use, time to next medically attended UTI, number of suspected UTIs, and UTI-related hospital admissions.ResultsOf 598 women eligible (mean [range] age, 58 [18-93] years), 303 were randomized to d-mannose (50.7%) and 295 to placebo (49.3%). Primary outcome data were available for 583 participants (97.5%). The proportion contacting ambulatory care with a clinically suspected UTI was 150 of 294 (51.0%) in the d-mannose group and 161 of 289 (55.7%) in the placebo group (risk difference, -5%; 95% CI, -13% to 3%; P = .26). Estimates were similar in per protocol analyses, imputation analyses, and preplanned subgroups. There were no statistically significant differences in any secondary outcome measures.Conclusions and relevanceIn this randomized clinical trial, daily d-mannose did not reduce the proportion of women with recurrent UTI in primary care who experienced a subsequent clinically suspected UTI. d-Mannose should not be recommended for prophylaxis in this patient group.Trial registrationisrctn.org Identifier: ISRCTN13283516.

Project description:Escherichia coli strains adhere to the normally sterile human uroepithelium using type 1 pili, that are long, hairy surface organelles exposing a mannose-binding FimH adhesin at the tip. A small percentage of adhered bacteria can successfully invade bladder cells, presumably via pathways mediated by the high-mannosylated uroplakin-Ia and alpha3beta1 integrins found throughout the uroepithelium. Invaded bacteria replicate and mature into dense, biofilm-like inclusions in preparation of fluxing and of infection of neighbouring cells, being the major cause of the troublesome recurrent urinary tract infections.We demonstrate that alpha-D-mannose based inhibitors of FimH not only block bacterial adhesion on uroepithelial cells but also antagonize invasion and biofilm formation. Heptyl alpha-D-mannose prevents binding of type 1-piliated E. coli to the human bladder cell line 5637 and reduces both adhesion and invasion of the UTI89 cystitis isolate instilled in mouse bladder via catheterization. Heptyl alpha-D-mannose also specifically inhibited biofilm formation at micromolar concentrations. The structural basis of the great inhibitory potential of alkyl and aryl alpha-D-mannosides was elucidated in the crystal structure of the FimH receptor-binding domain in complex with oligomannose-3. FimH interacts with Man alpha1,3Man beta1,4GlcNAc beta1,4GlcNAc in an extended binding site. The interactions along the alpha1,3 glycosidic bond and the first beta1,4 linkage to the chitobiose unit are conserved with those of FimH with butyl alpha-D-mannose. The strong stacking of the central mannose with the aromatic ring of Tyr48 is congruent with the high affinity found for synthetic inhibitors in which this mannose is substituted for by an aromatic group.The potential of ligand-based design of antagonists of urinary tract infections is ruled by the structural mimicry of natural epitopes and extends into blocking of bacterial invasion, intracellular growth and capacity to fluxing and of recurrence of the infection.

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

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