Functional flexibility of the FimH adhesin: insights from a random mutant library

A flow cytometry method for quantitative measurement and molecular investigation of the adhesion of bacteria to yeast cells

The study of microorganism interactions is important for understanding the organization and functioning of microbial consortia. Additionally, the interaction between yeast and bacteria is of interest in the field of health and nutrition area for the development of probiotics. To investigate these microbial interactions at the cellular and molecular levels, a simple, reliable, and quantitative method is proposed. We demonstrated that flow cytometry enables the measurement of interactions at a single-cell level by detecting and counting yeast cells with bound fluorescent bacteria. Imaging flow cytometry revealed that the number of bacteria attached to yeast followed a Gaussian distribution whose maximum reached 14 bacterial cells using a clinical Escherichia coli strain E22 and the laboratory yeast strain BY4741. We found that the dynamics of adhesion resemble a Langmuir adsorption model, albeit it is a rapid and almost irreversible process. This adhesion is dependent on the mannose-specific type 1 fimbriae, as E. coli mutants lacking these appendages no longer adhere to yeast. However, this type 1 fimbriae-dependent adhesion could involve additional yeast cell wall factors, since the interaction between bacteria and yeast mutants with altered mannan content remained comparable to that of wild-type yeast. In summary, flow cytometry is an appropriate method for studying bacteria-yeast adhesion, as well as for the high-throughput screening of candidate molecules likely to promote or counteract this interaction.

WGS of intrauterine E. coli from cows with early postpartum uterine infection reveals a non-uterine specific genotype and virulence factors

Escherichia coli has been attributed to playing a major role in a cascade of events that affect the prevalence and severity of uterine disease in cattle. The objectives of this project were to (i) define the association between the prevalence of specific antimicrobial resistance and virulence factor genes in E. coli with the clinical status related to uterine infection, (ii) identify the genetic relationship between E. coli isolates from cows with diarrhea, with mastitis, and with and without metritis, and (iii) determine the association between the phenotypic and genotypic antimicrobial resistance identified on the E. coli isolated from postpartum cattle. Bacterial isolates (n = 148) were obtained from a larger cross-sectional study. Cows were categorized into one of three clinical groups before enrollment: metritis, cows with purulent discharge, and control cows. For genomic comparison, public genomes (n = 130) from cows with diarrhea, mastitis, and metritis were included in a genome-wide association study, to evaluate differences between the drug classes or the virulence factor category among clinical groups. A distinct E. coli genotype associated with metritis could not be identified. Instead, a high genetic diversity among the isolates from uterine sources was present. A virulence factor previously associated with metritis (fimH) using PCR was not associated with metritis. There was moderate accuracy for whole-genome sequencing to predict phenotypic resistance, which varied depending on the antimicrobial tested. Findings from this study contradict the traditional pathotype classification and the unique intrauterine E. coli genotype associated with metritis in dairy cows.IMPORTANCEMetritis is a common infectious disease in dairy cattle and the second most common reason for treating a cow with antimicrobials. The pathophysiology of the disease is complex and is not completely understood. Specific endometrial pathogenic Escherichia coli have been reported to be adapted to the endometrium and sometimes lead to uterine disease. Unfortunately, the specific genomic details of the endometrial-adapted isolates have not been investigated using enough genomes to represent the genomic diversity of this organism to identify specific virulence genes that are consistently associated with disease development and severity. Results from this study provide key microbial ecological advances by elucidating and challenging accepted concepts for the role of Intrauterine E. coli in metritis in dairy cattle, especially contradicting the existence of a unique intrauterine E. coli genotype associated with metritis in dairy cows, which was not found in our study.

Population characteristics of pathogenic Escherichia coli in puerperal metritis of dairy cows in Ningxia region of China: a systemic taxa distribution of virulence factors and drug resistance genes

Escherichia coli (E. coli) is closely associated with the occurrence of puerperal metritis in dairy cows. E. coli carries some the virulence and multi-drug resistant genes, which pose a serious threat to the health of postpartum cows. In this study, E. coli was isolated and identified from the uterine contents of postpartum cows with puerperal metritis in the Ningxia region of China, and its phylogenetic subgroups were determined. Meanwhile, virulence and drug resistance genes carried by E. coli and drug sensitivity were detected, and the characteristics of virulence and drug resistance genes distribution in E. coli phylogroups were further analyzed. The results showed that the isolation rate of E. coli in puerperal metritis samples was 95.2%. E. coli was mainly divided into phylogroups B2 and D, followed by groups A and B1, and was more connected to O157:H7, O169:H4, and ECC-1470 type strains. The virulence genes were mainly dominated by ompF (100%), traT (100%), fimH (97%), papC (96%), csgA (95%), Ang43 (93.9%), and ompC (93%), and the resistance genes were dominated by TEM (99%), tetA (71.7%), aac(3)II (66.7%), and cmlA (53.5%). Additionally, it was observed that the virulence and resistance gene phenotypes could be divided into two subgroups, with subgroup B2 and D having the highest distributions. Drug sensitivity tests also revealed that the E. coli was most sensitive to the fluoroquinolones enrofloxacin, followed by macrolides, aminoglycosides, tetracyclines, β-lactams, peptides and sulfonamides, and least sensitive to lincosamides. These results imply that pathogenic E. coli, which induces puerperal metritis of dairy cows in the Ningxia region of China, primarily belongs to the group B2 and D, contains multiple virulence and drug resistance genes, Moreover, E. coli has evolved resistance to several drugs including penicillin, lincomycin, cotrimoxazole, and streptomycin. It will offer specific guidelines reference for the prevention and treatment of puerperal metritis in dairy cows with E. coli infections in the Ningxia region of China.

Screening of antigenic epitopes related to the adhesion of the avian Escherichia coli Type 1 Fimbrial Agglutinin Domain

BACKGROUND

Avian Escherichia coli (E.coli) type 1 fimbriae adhere to avian tracheal epithelial cells through the FimH protein. However, the adhesion-related antigen is still unknown. The purpose of this study was to analyze the antigenicity of the type 1 fimbrial FimH protein of wild-type avian E. coli, screen antigen epitopes, and prepare monoclonal antibodies (mAbs) that can block the adhesion of avian E. coli.

RESULTS

In this study, the nucleic acid homologies of MG2 (O11), TS12 (O18), and YR5 (O78) with K12 were 97.7%, 99.6%, and 97.7%, respectively, and the amino acid sequence similarity reached 98.7%, 99.3%, and 98.0%, respectively. The epitopes and hydrophilicities of the FimH proteins of these three strains were similar. The more obvious lectin domain epitopes were located at FimH protein positions 111-124 and 154-162. The mAbs 7C2 and 7D8 against these two epitopes were prepared. An adhesion inhibition test showed that 7C2 and 7D8 blocked bacterial adhesion to avian tracheal epithelial cells. The mAb 7C2 against the 111-124 epitope inhibited O78 strain adhesion by 93%, and the mAb 7D8 against the 154-162 epitope inhibited O78 strain adhesion by 49%, indicating that these two epitopes are closely related to the adhesion of type 1 fimbriae. However, only the 111-124 epitope-recognizing mAb 7C2 inhibited bacterial agglutination of erythrocytes, indicating that host cell receptor binding and erythrocyte agglutination are not mediated by the same spatial locations within the FimH protein.

CONCLUSIONS

The results demonstrate that the mAbs 7C2 and 7D8 against FimH protein positions 111-124 and 154-162 could inhibit the adhesion of E.coli to the chicken trachea.

Urinary Tract Infections Caused by Uropathogenic Escherichia coli: Mechanisms of Infection and Treatment Options

Urinary tract infections (UTIs) are common bacterial infections that represent a severe public health problem. They are often caused by Escherichia coli (E. coli), Klebsiella pneumoniae (K. pneumonia), Proteus mirabilis (P. mirabilis), Enterococcus faecalis (E. faecalis), and Staphylococcus saprophyticus (S. saprophyticus). Among these, uropathogenic E. coli (UPEC) are the most common causative agent in both uncomplicated and complicated UTIs. The adaptive evolution of UPEC has been observed in several ways, including changes in colonization, attachment, invasion, and intracellular replication to invade the urothelium and survive intracellularly. While antibiotic therapy has historically been very successful in controlling UTIs, high recurrence rates and increasing antimicrobial resistance among uropathogens threaten to greatly reduce the efficacy of these treatments. Furthermore, the gradual global emergence of multidrug-resistant UPEC has highlighted the need to further explore its pathogenesis and seek alternative therapeutic and preventative strategies. Therefore, a thorough understanding of the clinical status and pathogenesis of UTIs and the advantages and disadvantages of antibiotics as a conventional treatment option could spark a surge in the search for alternative treatment options, especially vaccines and medicinal plants. Such options targeting multiple pathogenic mechanisms of UPEC are expected to be a focus of UTI management in the future to help combat antibiotic resistance.

Bacterial Lectin FimH and Its Aggregation Hot-Spots: An Alternative Strategy against Uropathogenic Escherichia coli

Type I fimbriae are the main adhesive organelles of uropathogenic Escherichia coli (UPEC), consisting of four different subunits. Their component with the most important role in establishing bacterial infections is the FimH adhesin located at the fimbrial tip. This two-domain protein mediates adhesion to host epithelial cells through interaction with terminal mannoses on epithelial glycoproteins. Here, we propose that the amyloidogenic potential of FimH can be exploited for the development of therapeutic agents against Urinary Tract Infections (UTIs). Aggregation-prone regions (APRs) were identified via computational methods, and peptide-analogues corresponding to FimH lectin domain APRs were chemically synthesized and studied with the aid of both biophysical experimental techniques and molecular dynamic simulations. Our findings indicate that these peptide-analogues offer a promising set of antimicrobial candidate molecules since they can either interfere with the folding process of FimH or compete for the mannose-binding pocket.

Evidence of a possible multicellular life cycle in Escherichia coli

Biofilms are surface-attached multicellular microbial communities. Their genetics have been extensively studied, but the cell-scale morphogenetic events of their formation are largely unknown. Here, we recorded the entirety of morphogenesis in Escherichia coli, and discovered a previously unknown multicellular self-assembly process. Unattached, single-cells formed 4-cell rosettes which grew into constant-width chains. After ∼10 cell generations, these multicellular chains attached to surfaces and stopped growing. Chains remained clonal throughout morphogenesis. We showed that this process generates biofilms, which we found are composed of attached clonal chains, aligned in parallel. We investigated genetics of chain morphogenesis: Ag43 facilitates rosette formation and clonality; type-1 fimbriae and curli promote stability and configuration; and extracellular polysaccharide production facilitates attachment. Our study establishes that E. coli, a unicellular organism, can follow a multistage, clonal, genetically-regulated, rosette-initiated multicellular life cycle. These findings have implications for synthetic biology, multicellular development, and the treatment and prevention of bacterial diseases.

Modified horseshoe crab peptides target and kill bacteria inside host cells

Bacteria that occupy an intracellular niche can evade extracellular host immune responses and antimicrobial molecules. In addition to classic intracellular pathogens, other bacteria including uropathogenic Escherichia coli (UPEC) can adopt both extracellular and intracellular lifestyles. UPEC intracellular survival and replication complicates treatment, as many therapeutic molecules do not effectively reach all components of the infection cycle. In this study, we explored cell-penetrating antimicrobial peptides from distinct structural classes as alternative molecules for targeting bacteria. We identified two β-hairpin peptides from the horseshoe crab, tachyplesin I and polyphemusin I, with broad antimicrobial activity toward a panel of pathogenic and non-pathogenic bacteria in planktonic form. Peptide analogs [I11A]tachyplesin I and [I11S]tachyplesin I maintained activity toward bacteria, but were less toxic to mammalian cells than native tachyplesin I. This important increase in therapeutic window allowed treatment with higher concentrations of [I11A]tachyplesin I and [I11S]tachyplesin I, to significantly reduce intramacrophage survival of UPEC in an in vitro infection model. Mechanistic studies using bacterial cells, model membranes and cell membrane extracts, suggest that tachyplesin I and polyphemusin I peptides kill UPEC by selectively binding and disrupting bacterial cell membranes. Moreover, treatment of UPEC with sublethal peptide concentrations increased zinc toxicity and enhanced innate macrophage antimicrobial pathways. In summary, our combined data show that cell-penetrating peptides are attractive alternatives to traditional small molecule antibiotics for treating UPEC infection, and that optimization of native peptide sequences can deliver effective antimicrobials for targeting bacteria in extracellular and intracellular environments.

The glycobiology of uropathogenic E. coli infection: the sweet and bitter role of sugars in urinary tract immunity

Urinary tract infections (UTI) are among the most prevalent infectious diseases and the most common cause of nosocomial infections, worldwide. Uropathogenic E. coli (UPEC) are responsible for approximately 80% of all UTI, which most commonly affect the bladder. UPEC colonize the urinary tract by ascension of the urethra, followed by cell invasion, and proliferation inside and outside urothelial cells, thereby causing symptomatic infections and quiescent intracellular reservoirs that may lead to recurrence. Sugars, or glycans, are key molecules for host–pathogen interactions, and UTI are no exception. Surface glycans regulate many of the events associated with UPEC adhesion and infection, as well as induction of the host immune response. While the bacterial protein FimH binds mannose‐containing host glycoproteins to initiate infection and UPEC‐secreted polysaccharides block immune mechanisms to favour intracellular replication, host glycans on the urothelial surface and on secreted glycoproteins prevent or limit infection by inhibiting UPEC adhesion. Given the importance of glycans during UTI, here we review the glycobiology of UPEC infection to highlight fundamental sugar‐mediated processes of immunological interest for their potential clinical applications. Interdisciplinary approaches incorporating glycomics and infection biology may help to develop novel non‐antibiotic‐based therapeutic strategies for bacterial infections as the spread of antimicrobial‐resistant uropathogens is currently threatening modern healthcare systems.

FimH as a scaffold for regulated molecular recognition

Background

Recognition proteins are critical in many biotechnology applications and would be even more useful if their binding could be regulated. The current gold standard for recognition molecules, antibodies, lacks convenient regulation. Alternative scaffolds can be used to build recognition proteins with new functionalities, including regulated recognition molecules. Here we test the use of the bacterial adhesin FimH as a scaffold for regulated molecular recognition. FimH binds to its native small molecule target mannose in a conformation-dependent manner that can be regulated by two types of noncompetitive regulation: allosteric and parasteric.

Results

We demonstrate that conformational regulation of FimH can be maintained even after reengineering the binding site to recognize the non-mannosylated targets nickel or Penta-His antibody, resulting in an up to 7-fold difference in K_D between the two conformations. Moreover, both the allosteric and parasteric regulatory mechanisms native to FimH can be used to regulate binding to its new target. In one mutant, addition of the native ligand mannose parasterically improves the mutant’s affinity for Penta-His 4-fold, even as their epitopes overlap. In another mutant, the allosteric antibody mab21 reduces the mutant’s affinity for Penta-His 7-fold. The advantage of noncompetitive regulation is further illustrated by the ability of this allosteric regulator to induce 98% detachment of Penta-His, even with modest differences in affinity.

Conclusions

This illustrates the potential of FimH, with its deeply studied conformation-dependent binding, as a scaffold for conformationally regulated binding via multiple mechanisms.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13036-020-00253-2.

Restriction of chronic Escherichia coli urinary tract infection depends upon T cell-derived interleukin-17, a deficiency of which predisposes to flagella-driven bacterial persistence

Urinary tract infections (UTI) frequently progress to chronicity in infected individuals but the mechanisms of pathogenesis underlying chronic UTI are not well understood. We examined the role of interleukin (IL)-17A in UTI because this cytokine promotes innate defense against uropathogenic Escherichia coli (UPEC). Analysis of UPEC persistence and pyelonephritis in mice deficient in IL-17A revealed that UPEC CFT073 caused infection at a rate higher than the multidrug resistant strain EC958. Il17a^-/- mice exhibited pyelonephritis with kidney bacterial burdens higher than those of wild-type (WT) mice. Synthesis of IL-17A in the bladder reflected a combination of γδ-T and T_H 17 cell responses. Analysis of circulating inflammatory mediators at 24h postinoculation identified predictors of progression to chronicity, including IL-6 and monocyte chemoattractant protein-1 (MCP-1). Histological analysis identified infiltrating populations of neutrophils, NK cells, and γδ T cells in the bladder, whereas neutrophils predominated in the kidney. Analysis of the contribution of flagella to chronicity using hyper-flagellated and fliC-deficient UPEC in WT and Il17a^-/- mice revealed that, in a host that is deficient for the production of IL-17A, flagella contribute to bacterial persistence. These findings show a role for IL-17A in defense against chronic UTI and a contribution of flagella to the pathogenesis of infection.

Characterization of native Escherichia coli populations from bovine vagina of healthy heifers and cows with postpartum uterine disease

Even though Escherichia coli are common bacteria of the bovine vaginal microbiota, they represent an important pathogen that causes diseases in the reproductive tract and subfertility. However, the actual endometrial virulence profile of E. coli is poorly understood. The present study aims to characterize the phylogenetic structure and virulence potential of native vaginal populations of E. coli from healthy heifers (H), and cows with postpartum uterine diseases (PUD), such as metritis/endometritis (MT) or repeat breeder cows (RB). To this end, the virulence repertoire of 97 E. coli isolates was genotypically and phenotypically assessed. Most of them were assigned to phylogenetic group A (74%), followed by B1 (17%) and D (9%); RB strains were significantly (p < 0.05) more represented by B1. Seven of the 15 evaluated virulence genes (VFG) were detected and the most prevalent were fimH (87%), agn43 (41%) and csgA (35%); while traT (27%), fyuA (11%), hlyA (5%) and kpsMT II (5%) were observed in a lower proportion. Particularly, fyuA was significantly higher (p < 0.05) in MT cows whereas csgA showed the same behavior in PUD animals (p < 0.05). When comparing H and PUD strains, these last ones were associated to positive expression of biofilm, fimbriae curli/cellulose and motility; yet RB strains did not show motility. Vaginal B1 E. coli populations, that possess VFG (fyuA and csgA) as well as the expression of motility, curli fimbriae/cellulose and biofilm, may represent risk factors for endometrial disorders; specifically, those that also, have kpsMT II may have a pathogenic potential for causing the RB syndrome. Future research focusing on the detection of these strains in the vaginal microbiota of cows with postpartum uterine diseases should be done since the control of their presence in vagina could reduce the risk that they access the uterus during the postpartum period.

Identification of FimH derivatives as adjuvant vaccinated with PAc that enhance protection against Streptcoccus mutans colonization

FimH is the adhesin of type I fimbriae expressed on Escherichia coli that can mediate specific adherence to host cells. High binding mutations in FimH are related to the adaptive evolution of bacteria. However, additional roles that these allelic variations may play remain elusive. To investigate novel biological functions of the mutations in FimH, we introduced four different variants of FimH by incorporating single amino acid substitutions at specific sites, namely A25P, G73R, A106, and T158P, respectively. In this study, adjuvant potential of FimH variants was evaluated by investigating their ability to trigger innate immune response to DC2.4 and adaptive immunity to improve immunological characteristics. The data revealed that purified A106 and T158P up-regulated the expression of co-stimulatory molecules critically involved in DC2.4 activation by interaction with TLR4, whereas A25P and G73R did not induce the phenotypic maturation of DC2.4. Besides, the culture of DC2.4 with A106 and T158P enhanced the release of cytokines and protein phagocytosis. When formulated with PAc, T158P elicited more robust PAc-specific IgG and IgA antibody responses compared to PBS, PAc and PAc+K12 groups and inhibited bacteria colonization. Collectively, the results confirmed that the T158P mutation located around the inter-domain interface of the protein induced a specific enhancement effect on adjuvant characteristics.

Drug and Vaccine Development for the Treatment and Prevention of Urinary Tract Infections

Urinary tract infections (UTI) are among the most common bacterial infections in humans, affecting millions of people every year. UTI cause significant morbidity in women throughout their lifespan, in infant boys, in older men, in individuals with underlying urinary tract abnormalities, and in those that require long-term urethral catheterization, such as patients with spinal cord injuries or incapacitated individuals living in nursing homes. Serious sequelae include frequent recurrences, pyelonephritis with sepsis, renal damage in young children, pre-term birth, and complications of frequent antimicrobial use including high-level antibiotic resistance and Clostridium difficile colitis. Uropathogenic E. coli (UPEC) cause the vast majority of UTI, but less common pathogens such as Enterococcus faecalis and other enterococci frequently take advantage of an abnormal or catheterized urinary tract to cause opportunistic infections. While antibiotic therapy has historically been very successful in controlling UTI, the high rate of recurrence remains a major problem, and many individuals suffer from chronically recurring UTI, requiring long-term prophylactic antibiotic regimens to prevent recurrent UTI. Furthermore, the global emergence of multi-drug resistant UPEC in the past ten years spotlights the need for alternative therapeutic and preventative strategies to combat UTI, including anti-infective drug therapies and vaccines. In this chapter, we review recent advances in the field of UTI pathogenesis, with an emphasis on the identification of promising drug and vaccine targets. We then discuss the development of new UTI drugs and vaccines, highlighting the challenges these approaches face and the need for a greater understanding of urinary tract mucosal immunity.

Adhesion of Escherichia coli under flow conditions reveals potential novel effects of FimH mutations

FimH-mediated adhesion of Escherichia coli to bladder epithelium is a prerequisite for urinary tract infections. FimH is also essential for blood-borne bacterial dissemination, but the mechanisms are poorly understood. The purpose of this study was to assess the influence of different FimH mutations on bacterial adhesion using a novel adhesion assay, which models the physiological flow conditions bacteria are exposed to. We introduced 12 different point mutations in the mannose binding pocket of FimH in an E. coli strain expressing type 1 fimbriae only (MSC95-FimH). We compared the bacterial adhesion of each mutant across several commonly used adhesion assays, including agglutination of yeast, adhesion to mono- and tri-mannosylated substrates, and static adhesion to bladder epithelial and endothelial cells. We performed a comparison of these assays to a novel method that we developed to study bacterial adhesion to mammalian cells under flow conditions. We showed that E. coli MSC95-FimH adheres more efficiently to microvascular endothelium than to bladder epithelium, and that only endothelium supports adhesion at physiological shear stress. The results confirmed that mannose binding pocket mutations abrogated adhesion. We demonstrated that FimH residues E50 and T53 are crucial for adhesion under flow conditions. The coating of endothelial cells on biochips and modelling of physiological flow conditions enabled us to identify FimH residues crucial for adhesion. These results provide novel insights into screening methods to determine the effect of FimH mutants and potentially FimH antagonists.

Comprehensive analysis of type 1 fimbriae regulation in fimB-null strains from the multidrug resistant Escherichia coli ST131 clone

Uropathogenic Escherichia coli (UPEC) of sequence type 131 (ST131) are a pandemic multidrug resistant clone associated with urinary tract and bloodstream infections. Type 1 fimbriae, a major UPEC virulence factor, are essential for ST131 bladder colonization. The globally dominant sub-lineage of ST131 strains, clade C/H30-R, possess an ISEc55 insertion in the fimB gene that controls phase-variable type 1 fimbriae expression via the invertible fimS promoter. We report that inactivation of fimB in these strains causes altered regulation of type 1 fimbriae expression. Using a novel read-mapping approach based on Illumina sequencing, we demonstrate that 'off' to 'on' fimS inversion is reduced in these strains and controlled by recombinases encoded by the fimE and fimX genes. Unlike typical UPEC strains, the nucleoid-associated H-NS protein does not strongly repress fimE transcription in clade C ST131 strains. Using a genetic screen to identify novel regulators of fimE and fimX in the clade C ST131 strain EC958, we defined a new role for the guaB gene in the regulation of type 1 fimbriae and in colonisation of the mouse bladder. Our results provide a comprehensive analysis of type 1 fimbriae regulation in ST131, and highlight important differences in its control compared to non-ST131 UPEC.

Integrated Pathophysiology of Pyelonephritis

Pyelonephritis represents a subset of urinary tract infections that occur from bacteria ascending from the lower to the upper reaches of the genitourinary system, such as the kidney. The renal system contains a range of hydrodynamically and immunologically challenging, interconnected microenvironments where the invading pathogen may populate during the course of the infection. The situation at the infection foci changes dynamically, vacillating between bacterial colonization and clearance, to which the outcome is a summation of all host-pathogen elements in play. A selection of important determinants includes factors of microbial origin, effects of eukaryotic cell signaling, physiological facets of the infected organ, and signals from distal organs. Improved understanding of the multifactorial aspects of molecular pathogenesis of infection requires intravital, cross-disciplinary approaches with high spatio-temporal resolution. The advancement of such approaches promises to eventually provide a comprehensive understanding of the integrated pathophysiology of pyelonephritis.

Efficient Cadmium Bioaccumulation by Displayed Hybrid CS3 Pili: Effect of Heavy Metal Binding Motif Insertion Site on Adsorption Capacity and Selectivity

The objective of this study was to evaluate the influence of insertion site of the metal binding motif on the bioaccumulation capacity of the hybrid CS3 pili displayed on the surface of Escherichia coli using both computational and experimental methods. Two metal binding motifs (cadmium binding motif (cbm) and cadmium binding beta motif (cbβm)), identified by searching against the PROSITE database, were inserted into five putative permissive sites of CstH protein (CS3 pili subunit) by using SOEing PCR technique. The expression and surface display of the hybrid pili were evaluated using dot and Western blotting methods and also immunofluorescence microscopy. The cadmium binding affinity and selectivity of the recombinant bacteria displaying various hybrid pili were evaluated using atomic absorption procedure. The results showed that the cadmium binding motifs enabled the cells to sequester cadmium 8- to 16-fold higher than the E.coli expressing native pili. The location of the metal binding motifs in the pili subunit had also a significant effect on the metal-binding properties of the hybrid pili. The insertion at positions 107-108 and 92-93 of the mature CstH showed the highest adsorption in comparison to other positions.

Urinary tract infection of mice to model human disease: Practicalities, implications and limitations

Urinary tract infections (UTIs) are among the most common bacterial infections in humans. Murine models of human UTI are vital experimental tools that have helped to elucidate UTI pathogenesis and advance knowledge of potential treatment and infection prevention strategies. Fundamentally, several variables are inherent in different murine models, and understanding the limitations of these variables provides an opportunity to understand how models may be best applied to research aimed at mimicking human disease. In this review, we discuss variables inherent in murine UTI model studies and how these affect model usage, data analysis and data interpretation. We examine recent studies that have elucidated UTI host-pathogen interactions from the perspective of gene expression, and review new studies of biofilm and UTI preventative approaches. We also consider potential standards for variables inherent in murine UTI models and discuss how these might expand the utility of models for mimicking human disease and uncovering new aspects of pathogenesis.

The co-transcriptome of uropathogenic Escherichia coli-infected mouse macrophages reveals new insights into host-pathogen interactions

Urinary tract infections (UTI) are among the most common infections in humans. Uropathogenic Escherichia coli (UPEC) can invade and replicate within bladder epithelial cells, and some UPEC strains can also survive within macrophages. To understand the UPEC transcriptional programme associated with intramacrophage survival, we performed host–pathogen co‐transcriptome analyses using RNA sequencing. Mouse bone marrow‐derived macrophages (BMMs) were challenged over a 24 h time course with two UPEC reference strains that possess contrasting intramacrophage phenotypes: UTI89, which survives in BMMs, and 83972, which is killed by BMMs. Neither of these strains caused significant BMM cell death at the low multiplicity of infection that was used in this study. We developed an effective computational framework that simultaneously separated, annotated and quantified the mammalian and bacterial transcriptomes. Bone marrow‐derived macrophages responded to the two UPEC strains with a broadly similar gene expression programme. In contrast, the transcriptional responses of the UPEC strains diverged markedly from each other. We identified UTI89 genes up‐regulated at 24 h post‐infection, and hypothesized that some may contribute to intramacrophage survival. Indeed, we showed that deletion of one such gene (pspA) significantly reduced UTI89 survival within BMMs. Our study provides a technological framework for simultaneously capturing global changes at the transcriptional level in co‐cultures, and has generated new insights into the mechanisms that UPEC use to persist within the intramacrophage environment.

Occurrence and expression of bacterial human virulence gene homologues in natural soil bacteria

The presence and in vitro expression of homologues to 22 bacterial human virulence determinants amongst culturable soil bacteria were investigated. About 25% of the bacterial isolates contained virulence gene homologues representing toxin (hblA, cytK2), adhesin (fimH), regulator (phoQ) and resistance (yfbI) determinants in pathogenic bacteria. The homologues of the toxin genes were found in Actinobacteria and Firmicutes (hblA), and in Firmicutes and Alpha- and Gammaproteobacteria (cytK2). The homologues to the type 1 fimbrial adhesin gene, fimH, and the L-Ara4N transferase gene, yfbI, were observed in Actinobacteria, Firmicutes and Gammaproteobacteria. The regulator gene, phoQ, was only found in Gammaproteobacteria. The presence of cytK2 in Alpha- and Gammaproteobacteria, fimH in Actinobacteria and Firmicutes, and hblA in Actinobacteria has not previously been described. A close sequence similarity (84-100%) was observed between the genes of environmental and clinical isolates, and expression assays suggested that the genes in some cases were expressed in vitro. The presence of functional virulence gene homologues underpins their importance for the survival of environmental bacteria. Furthermore, the high degree of sequence conservation to clinical sequences indicates that natural environments may be 'evolutionary cribs' of emerging pathogens.

Single clinical isolates from acute uncomplicated urinary tract infections are representative of dominant in situ populations

Urinary tract infections (UTIs) are one of the most commonly acquired bacterial infections in humans, and uropathogenic Escherichia coli strains are responsible for over 80% of all cases. The standard method for identification of uropathogens in clinical laboratories is cultivation, primarily using solid growth media under aerobic conditions, coupled with morphological and biochemical tests of typically a single isolate colony. However, these methods detect only culturable microorganisms, and characterization is phenotypic in nature. Here, we explored the genotypic identity of communities in acute uncomplicated UTIs from 50 individuals by using culture-independent amplicon pyrosequencing and whole-genome and metagenomic shotgun sequencing. Genus-level characterization of the UTI communities was achieved using the 16S rRNA gene (V8 region). Overall UTI community richness was very low in comparison to other human microbiomes. We strain-typed Escherichia-dominated UTIs using amplicon pyrosequencing of the fimbrial adhesin gene, fimH. There were nine highly abundant fimH types, and each UTI sample was dominated by a single type. Molecular analysis of the corresponding clinical isolates revealed that in the majority of cases the isolate was representative of the dominant taxon in the community at both the genus and the strain level. Shotgun sequencing was performed on a subset of eight E. coli urine UTI and isolate pairs. The majority of UTI microbial metagenomic sequences mapped to isolate genomes, confirming the results obtained using phylogenetic markers. We conclude that for the majority of acute uncomplicated E. coli-mediated UTIs, single cultured isolates are diagnostic of the infection.

In clinical practice, the diagnosis and treatment of acute uncomplicated urinary tract infection (UTI) are based on analysis of a single bacterial isolate cultured from urine, and it is assumed that this isolate represents the dominant UTI pathogen. However, these methods detect only culturable bacteria, and the existence of multiple pathogens as well as strain diversity within a single infection is not examined. Here, we explored bacteria present in acute uncomplicated UTIs using culture-independent sequence-based methods. Escherichia coli was the most common organism identified, and analysis of E. coli dominant UTI samples and their paired clinical isolates revealed that in the majority of infections the cultured isolate was representative of the dominant taxon at both the genus and the strain level. Our data demonstrate that in most cases single cultured isolates are diagnostic of UTI and are consistent with the notion of bottlenecks that limit strain diversity during UTI pathogenesis.

A FimH inhibitor prevents acute bladder infection and treats chronic cystitis caused by multidrug-resistant uropathogenic Escherichia coli ST131

BACKGROUND

Escherichia coli O25b:H4-ST131 represents a predominant clone of multidrug-resistant uropathogens currently circulating worldwide in hospitals and the community. Urinary tract infections (UTIs) caused by E. coli ST131 are typically associated with limited treatment options and are often recurrent.

METHODS

Using established mouse models of acute and chronic UTI, we mapped the pathogenic trajectory of the reference E. coli ST131 UTI isolate, strain EC958.

RESULTS

We demonstrated that E. coli EC958 can invade bladder epithelial cells and form intracellular bacterial communities early during acute UTI. Moreover, E. coli EC958 persisted in the bladder and established chronic UTI. Prophylactic antibiotic administration failed to prevent E. coli EC958-mediated UTI. However, 1 oral dose of a small-molecular-weight compound that inhibits FimH, the type 1 fimbriae adhesin, significantly reduced bacterial colonization of the bladder and prevented acute UTI. Treatment of chronically infected mice with the same FimH inhibitor lowered their bladder bacterial burden by >1000-fold.

CONCLUSIONS

In this study, we provide novel insight into the pathogenic mechanisms used by the globally disseminated E. coli ST131 clone during acute and chronic UTI and establish the potential of FimH inhibitors as an alternative treatment against multidrug-resistant E. coli.

[Virulence factors and pathophysiology of extraintestinal pathogenic Escherichia coli]

Extraintestinal pathogenic Escherichia coli (ExPEC) causing urinary tract infections, bacteraemia or meningitis are characterized by a particular genetic background (phylogenetic group B2 and D) and the presence, within genetic pathogenicity islands (PAI) or plasmids, of genes encoding virulence factors involved in adhesion to epithelia, crossing of the body barriers (digestive, kidney, bloodbrain), iron uptake and resistance to the immune system. Among the many virulence factors described, two are particularly linked with a pathophysiological process: type P pili PapGII adhesin is linked with acute pyelonephritis, in the absence of abnormal flow of urine, and the K1 capsule is linked with neonatal meningitis. However, if the adhesin PapGII appears as the key factor of pyelonephritis, such that its absence in strain causing the infection is predictive of malformation or a vesico-ureteral reflux, the meningeal virulence of E. coli can not be reduced to a single virulence factor, but results from a combination of factors unique to each clone, and an imbalance between the immune defenses of the host and bacterial virulence.

Host-pathogen checkpoints and population bottlenecks in persistent and intracellular uropathogenic Escherichia coli bladder infection

Bladder infections affect millions of people yearly, and recurrent symptomatic infections (cystitis) are very common. The rapid increase in infections caused by multidrug-resistant uropathogens threatens to make recurrent cystitis an increasingly troubling public health concern. Uropathogenic Escherichia coli (UPEC) cause the vast majority of bladder infections. Upon entry into the lower urinary tract, UPEC face obstacles to colonization that constitute population bottlenecks, reducing diversity, and selecting for fit clones. A critical mucosal barrier to bladder infection is the epithelium (urothelium). UPEC bypass this barrier when they invade urothelial cells and form intracellular bacterial communities (IBCs), a process which requires type 1 pili. IBCs are transient in nature, occurring primarily during acute infection. Chronic bladder infection is common and can be either latent, in the form of the quiescent intracellular reservoir (QIR), or active, in the form of asymptomatic bacteriuria (ASB/ABU) or chronic cystitis. In mice, the fate of bladder infection, QIR, ASB, or chronic cystitis, is determined within the first 24 h of infection and constitutes a putative host-pathogen mucosal checkpoint that contributes to susceptibility to recurrent cystitis. Knowledge of these checkpoints and bottlenecks is critical for our understanding of bladder infection and efforts to devise novel therapeutic strategies.

Ralstonia syzygii, the Blood Disease Bacterium and some Asian R. solanacearum strains form a single genomic species despite divergent lifestyles

The Ralstonia solanacearum species complex includes R. solanacearum, R. syzygii, and the Blood Disease Bacterium (BDB). All colonize plant xylem vessels and cause wilt diseases, but with significant biological differences. R. solanacearum is a soilborne bacterium that infects the roots of a broad range of plants. R. syzygii causes Sumatra disease of clove trees and is actively transmitted by cercopoid insects. BDB is also pathogenic to a single host, banana, and is transmitted by pollinating insects. Sequencing and DNA-DNA hybridization studies indicated that despite their phenotypic differences, these three plant pathogens are actually very closely related, falling into the Phylotype IV subgroup of the R. solanacearum species complex. To better understand the relationships among these bacteria, we sequenced and annotated the genomes of R. syzygii strain R24 and BDB strain R229. These genomes were compared to strain PSI07, a closely related Phylotype IV tomato isolate of R. solanacearum, and to five additional R. solanacearum genomes. Whole-genome comparisons confirmed previous phylogenetic results: the three phylotype IV strains share more and larger syntenic regions with each other than with other R. solanacearum strains. Furthermore, the genetic distances between strains, assessed by an in-silico equivalent of DNA-DNA hybridization, unambiguously showed that phylotype IV strains of BDB, R. syzygii and R. solanacearum form one genomic species. Based on these comprehensive data we propose a revision of the taxonomy of the R. solanacearum species complex. The BDB and R. syzygii genomes encoded no obvious unique metabolic capacities and contained no evidence of horizontal gene transfer from bacteria occupying similar niches. Genes specific to R. syzygii and BDB were almost all of unknown function or extrachromosomal origin. Thus, the pathogenic life-styles of these organisms are more probably due to ecological adaptation and genomic convergence during vertical evolution than to the acquisition of DNA by horizontal transfer.

Fimbrial adhesins from extraintestinal Escherichia coli

Extraintestinal pathogenic Escherichia coli (ExPEC) represent an important subclass of E. coli that cause a wide spectrum of diseases in human and animal hosts. Fimbriae are key virulence factors of ExPEC strains. These long surface located rod-shaped organelles mediate receptor-specific attachment to host tissue surfaces (tissue tropism). Some ExPEC fimbriae have additional functions such as the promotion of biofilm formation, cell aggregation and adherence to abiotic surfaces. Here we review the structure, function and contribution to virulence of fimbriae associated with ExPEC strains.

A bivalent glycopeptide to target two putative carbohydrate binding sites on FimH

FimH is a mannose-specific bacterial lectin found on type 1 fimbriae with a monovalent carbohydrate recognition domain (CRD) that is known from X-ray studies. However, binding studies with multivalent ligands have suggested an additional carbohydrate-binding site on this protein. In order to prove this hypothesis, a bivalent glycopeptide ligand with the capacity to bridge two putative carbohydrate binding sites on FimH was designed and synthesized. Anti-adhesion assays with the new bivalent ligand and type 1-fimbriated bacteria have revealed, that verification of the number of carbohydrate binding sites on FimH with a tailor-made bivalent glycopeptide requires further investigation to be conclusive.

Pathogenomic comparison of human extraintestinal and avian pathogenic Escherichia coli--search for factors involved in host specificity or zoonotic potential

Avian pathogenic Escherichia coli (APEC) and human extraintestinal pathogenic E. coli (ExPEC) cause various diseases in humans and animals and cannot be clearly distinguished by molecular epidemiology and genome content. We characterized traits of eight representative human ExPEC and APEC variants to either support the zoonotic potential or indicate factors involved in host specificity. These strains were very similar regarding phylogeny, virulence gene content and allelic variation of adhesins. Host- or serogroup-specific differences in type 1-, P-, S/F1C-fimbriae, curli, flagella, colicin and aerobactin expression or in vivo virulence were not found. Serogroup-dependent differences in genome content may depend on the phylogenetic background. To identify traits involved in host specificity, we performed transcriptome analysis of human ExPEC IHE3034 and APEC BEN374 in response to human (37 degrees C) or avian (41 degrees C) body temperature. Both isolates displayed similar transcriptional profiles at both temperatures. Transcript levels of motility/chemotaxis genes were repressed at 41 degrees C. The hdeAB and cadA genes involved in acid stress resistance, although often induced at 41 degrees C, could not be correlated with host specificity. Beside strain-specific effects, the common behavior of both strains at human or avian body temperature supports the idea of a potential zoonotic risk of certain human ExPEC and APEC variants.

Escherichia coli isolates causing asymptomatic bacteriuria in catheterized and noncatheterized individuals possess similar virulence properties

Urinary tract infections (UTIs) are among the most common infectious diseases of humans, with Escherichia coli being responsible for >80% of all cases. Asymptomatic bacteriuria (ABU) occurs when bacteria colonize the urinary tract without causing clinical symptoms and can affect both catheterized patients (catheter-associated ABU [CA-ABU]) and noncatheterized patients. Here, we compared the virulence properties of a collection of ABU and CA-ABU nosocomial E. coli isolates in terms of antibiotic resistance, phylogenetic grouping, specific UTI-associated virulence genes, hemagglutination characteristics, and biofilm formation. CA-ABU isolates were similar to ABU isolates with regard to the majority of these characteristics; exceptions were that CA-ABU isolates had a higher prevalence of the polysaccharide capsule marker genes kpsMT II and kpsMT K1, while more ABU strains were capable of mannose-resistant hemagglutination. To examine biofilm growth in detail, we performed a global gene expression analysis with two CA-ABU strains that formed a strong biofilm and that possessed a limited adhesin repertoire. The gene expression profile of the CA-ABU strains during biofilm growth showed considerable overlap with that previously described for the prototype ABU E. coli strain, 83972. This is the first global gene expression analysis of E. coli CA-ABU strains. Overall, our data suggest that nosocomial ABU and CA-ABU E. coli isolates possess similar virulence profiles.

Adhesive organelles of Gram-negative pathogens assembled with the classical chaperone/usher machinery: structure and function from a clinical standpoint

This review summarizes current knowledge on the structure, function, assembly and biomedical applications of the superfamily of adhesive fimbrial organelles exposed on the surface of Gram-negative pathogens with the classical chaperone/usher machinery. High-resolution three-dimensional (3D) structure studies of the minifibers assembling with the FGL (having a long F1-G1 loop) and FGS (having a short F1-G1 loop) chaperones show that they exploit the same principle of donor-strand complementation for polymerization of subunits. The 3D structure of adhesive subunits bound to host-cell receptors and the final architecture of adhesive fimbrial organelles reveal two functional families of the organelles, respectively, possessing polyadhesive and monoadhesive binding. The FGL and FGS chaperone-assembled polyadhesins are encoded exclusively by the gene clusters of the γ3- and κ-monophyletic groups, respectively, while gene clusters belonging to the γ1-, γ2-, γ4-, and π-fimbrial clades exclusively encode FGS chaperone-assembled monoadhesins. Novel approaches are suggested for a rational design of antimicrobials inhibiting the organelle assembly or inhibiting their binding to host-cell receptors. Vaccines are currently under development based on the recombinant subunits of adhesins.

FimH alleles direct preferential binding of Salmonella to distinct mammalian cells or to avian cells

This study aimed to determine whether allelic variants of the FimH adhesin from Salmonella enterica confer differential bacterial binding to different types of mammalian cells [murine bone marrow-derived dendritic cells (DCs) and HEp-2 cells] and chicken leukocytes. Although the type 1 fimbriated S. enterica serovar Typhimurium strains AJB3 (SR-11 derivative) and SL1344 both aggregated yeast cells, only the former bound efficiently to DCs and HEp-2 cells. Type 1 fimbriae-mediated binding to DCs having previously been shown to require the FimH adhesin and to be inhibited by mannose, FimH sequences from strains SL1344 and AJB3 were compared and found to differ by only one residue, asparagine 158 in SL1344 being replaced by a tyrosine in AJB3. The importance of residue 158 for FimH-mediated binding was further confirmed in recombinant Escherichia coli expressing S. enterica type 1 fimbriae with a variety of substitutions engineered at this position. Additional studies with the 'non-adhesive' FimH of a type 2 fimbriated S. enterica serovar Gallinarum showed that this FimH did not mediate bacterial binding to murine DCs or HEp-2 cells. However, the type 2 FimH significantly improved bacterial adhesion to chicken leukocytes, in comparison to the type 1 FimH of strain AJB3, attributing for the first time a function to the type 2 fimbriae of S. enterica. Consequently, our data show that allelic variation of the S. enterica FimH adhesin directs not only host-cell-specific recognition, but also distinctive binding to mammalian or avian receptors. It is most relevant that this allele-specific binding profile parallels the host specificity of the respective FimH-expressing pathogen.

Genotypic analyses of uropathogenic Escherichia coli based on fimH single nucleotide polymorphisms (SNPs)

The application of genotyping techniques for subtyping uropathogenic Escherichia coli has contributed to better understanding of the epidemiology of community-acquired urinary tract infection (UTI). However, the current techniques are hampered by limited reproducibility, poor discriminatory power, labour-intensive performance or high cost. A screening test that is sequence-based would provide an inexpensive, reproducible way to subtype E. coli isolates. Such a test, if also discriminatory, would be highly useful for epidemiological studies. The discriminatory ability of 12 putative virulence genes (fimH, fliD, fliM, iha, motA, papA/H, kpsMTII, fepE, fimA, flgA, malG, purD) was evaluated based on single nucleotide polymorphisms (SNPs) in nine uropathogenic E. coli isolates, all previously found to belong to a single multilocus sequence type (MLST) complex (ST69). An additional 25 epidemiologically well-characterized E. coli isolates belonging to 12 distinct MLST clonal complexes were analysed for fimH SNP. None of the 12 genes except fimH were able to further discriminate the nine ST69-complex strains. Isolates belonging to the 12 non-ST69 MLST groups were separated into 10 fimH SNP subgroups. While fimH SNP analysis may not be an appropriate phylogenetic method, it offers discriminatory power similar to that of MLST and could be used as a simple, inexpensive screening test for epidemiological studies of uropathogenic E. coli.

Identification of type 3 fimbriae in uropathogenic Escherichia coli reveals a role in biofilm formation

Catheter-associated urinary tract infection (CAUTI) is the most common nosocomial infection in the United States. Uropathogenic Escherichia coli (UPEC), the most common cause of CAUTI, can form biofilms on indwelling catheters. Here, we identify and characterize novel factors that affect biofilm formation by UPEC strains that cause CAUTI. Sixty-five CAUTI UPEC isolates were characterized for phenotypic markers of urovirulence, including agglutination and biofilm formation. One isolate, E. coli MS2027, was uniquely proficient at biofilm growth despite the absence of adhesins known to promote this phenotype. Mini-Tn5 mutagenesis of E. coli MS2027 identified several mutants with altered biofilm growth. Mutants containing insertions in genes involved in O antigen synthesis (rmlC and manB) and capsule synthesis (kpsM) possessed enhanced biofilm phenotypes. Three independent mutants deficient in biofilm growth contained an insertion in a gene locus homologous to the type 3 chaperone-usher class fimbrial genes of Klebsiella pneumoniae. These type 3 fimbrial genes (mrkABCDF), which were located on a conjugative plasmid, were cloned from E. coli MS2027 and could complement the biofilm-deficient transconjugants when reintroduced on a plasmid. Primers targeting the mrkB chaperone-encoding gene revealed its presence in CAUTI strains of Citrobacter koseri, Citrobacter freundii, Klebsiella pneumoniae, and Klebsiella oxytoca. All of these mrkB-positive strains caused type 3 fimbria-specific agglutination of tannic acid-treated red blood cells. This is the first description of type 3 fimbriae in E. coli, C. koseri, and C. freundii. Our data suggest that type 3 fimbriae may contribute to biofilm formation by different gram-negative nosocomial pathogens.

Interdomain Interaction in the FimH Adhesin of Escherichia coli Regulates the Affinity to Mannose

FimH is a mannose-specific adhesin located on the tip of type 1 fimbriae of Escherichia coli that is capable of mediating shear-enhanced bacterial adhesion. FimH consists of a fimbria-associated pilin domain and a mannose-binding lectin domain, with the binding pocket positioned opposite the interdomain interface. By using the yeast two-hybrid system, purified lectin and pilin domains, and docking simulations, we show here that the FimH domains interact with one another. The affinity for mannose is greatly enhanced (up to 300-fold) in FimH variants in which the interdomain interaction is disrupted by structural mutations in either the pilin or lectin domains. Also, affinity to mannose is dramatically enhanced in isolated lectin domains or in FimH complexed with the chaperone molecule that is wedged between the domains. Furthermore, FimH with native structure mediates weak binding at low shear stress but shifts to strong binding at high shear, whereas FimH with disrupted interdomain contacts (or the isolated lectin domain) mediates strong binding to mannose-coated surfaces even under low shear. We propose that interactions between lectin and pilin domains decrease the affinity of the mannose-binding pocket via an allosteric mechanism. We further suggest that mechanical force at high shear stress separates the two domains, allowing the lectin domain to switch from a low affinity to a high affinity state. This shift provides a mechanism for FimH-mediated shear-enhanced adhesion by enabling the adhesin to form catch bond-like interactions that are longer lived at high tensile force.

The role of F9 fimbriae of uropathogenic Escherichia coli in biofilm formation

Uropathogenic Escherichia coli (UPEC) is the primary cause of urinary tract infection (UTI) in the developed world. The major factors associated with virulence of UPEC are fimbrial adhesins, which mediate attachment to specific receptors, enhance persistence and trigger innate host responses. UPEC produce a range of fimbrial adhesins, with type 1 and P fimbriae of the chaperone-usher subclass being the best characterized. The prototype UPEC strain CFT073 contains ten gene clusters that contain genes characteristic of this class of fimbriae. However, only five of these gene clusters have been characterized in detail. In this study the F9 fimbrial gene cluster (c1931-c1936) from CFT073 has been characterized. The F9 fimbriae-encoding genes were PCR amplified, cloned and expressed in a K-12 background devoid of type 1 fimbriae. While F9 fimbrial expression was not associated with any haemagglutination or cellular adherence properties, a role in biofilm formation was observed. E. coli K-12 cells expressing F9 fimbriae produced a dense and uniform biofilm in both microtitre plate and continuous-flow biofilm model systems. In wild-type UPEC CFT073, expression of the F9 major subunit-encoding gene was detected during exponential growth in M9 minimal medium. F9 expression could also be detected following selection and enrichment for pellicle growth in a CFT073fim foc double mutant. The F9 genes appear to be common in UPEC and other types of pathogenic E. coli. However, their precise contribution to disease remains to be determined.

Do type 1 fimbriae promote inflammation in the human urinary tract?

Type 1 fimbriae have been implicated as virulence factors in animal models of urinary tract infection (UTI), but the function in human disease remains unclear. This study used a human challenge model to examine if type 1 fimbriae trigger inflammation in the urinary tract. The asymptomatic bacteriuria strain Escherichia coli 83972, which fails to express type 1 fimbriae, due to a 4.25 kb fimB-fimD deletion, was reconstituted with a functional fim gene cluster and fimbrial expression was monitored through a gfp reporter. Each patient was inoculated with the fim+ or fim- variants on separate occasions, and the host response to type 1 fimbriae was quantified by intraindividual comparisons of the responses to the fim+ or fim- isogens, using cytokines and neutrophils as end-points. Type 1 fimbriae did not promote inflammation and adherence was poor, as examined on exfoliated cells in urine. This was unexpected, as type 1 fimbriae enhanced the inflammatory response to the same strain in the murine urinary tract and as P fimbrial expression by E. coli 83972 enhances adherence and inflammation in challenged patients. We conclude that type 1 fimbriae do not contribute to the mucosal inflammatory response in the human urinary tract.

Intestinal versus external growth conditions change the surficial properties in a collection of environmental Escherichia coli isolates

Predicting the fate of microorganisms in the environment is increasingly warranted, especially for pathogenic strains. A major habitat of Escherichia coli, which encompasses commensal as well as pathogenic strains, is the gastrointestinal tract with conditions very different from the environment it encounters after shedding from the host or during cultivation in the laboratory. We developed two relevant growth conditions representative of intestinal (host-associated) and external (postshedding) environments to investigate the surficial properties and behaviors of a diverse subset of E. coli feedlot isolates. Surficial properties may determine an isolate's physical fate. A pronounced increase in cell hydrophobicity and concomitant biofilm mass formation was observed for isolates grown under external conditions. Isolates that exhibited the highest surface hydrophobicity also formed visible suspended aggregates under external conditions. Other than hydrophobicity, flagella-mediated motility was determinant in affecting E. coli biofilm formation under external conditions, with all four nonmotile E. coli isolates characterized as thin-biofilm formers. The majority (88%) of Ag43+ (outer membrane protein, antigen 43) isolates formed thick biofilms, whereas the majority (75%) of Ag43- isolates formed thin biofilms. The tested E. coli O157:H7 strain behaved differently from the environmental E. coli isolates: it displayed a low electrostatic charge, a small decrease in hydrophobicity upon shifts to external conditions, and very little biofilm formation. On the other hand, the commonly used laboratory strain E. coli K-12 displayed low hydrophobicity both intestinally and externally, but it formed significant biofilm mass under external conditions. Clearly, various E. coli strains manifest significant variability in surficial behavior. This variability is further modulated by growth conditions. The interacting strain-inherent and cultivation-dependent effects on surficial behavior may have broad consequences for the fate and ecology of pathogenic and commensal E. coli strains.

Sticky fibers and uropathogenesis: bacterial adhesins in the urinary tract

Adhesins mediate the introduction of bacteria to the host in the sometimes life-long relationship of uropathogenic Esherichia coli (UPEC) and the human urinary tract. As a class of extracellular proteins, adhesins enable bacteria to adhere to and, in some cases, invade host tissue; adhesins render UPEC virulent and permit host colonization. Adhesin receptor interactions at the host interface determine tissue tropism and disease progression in that niche, with each adhesin preferring unique sites within the urinary tract. This review focuses on known adhesins implicated in uropathogenesis, the structural basis of tissue tropism, postinvasion intracellular replication, current therapeutic design strategies, and newly discovered fimbrial gene clusters that may play a role in urinary tract infections.

Molecular characterization of the Escherichia coli asymptomatic bacteriuria strain 83972: the taming of a pathogen

Escherichia coli 83972 is a clinical asymptomatia bacteriuric isolate that is able to colonize the human urinary bladder without inducing an immune response. Here we demonstrate that one of the mechanisms by which this strain has become attenuated is through the mutation of its genes encoding type 1 and P fimbriae.

Biodiversity-based identification and functional characterization of the mannose-specific adhesin of Lactobacillus plantarum

Lactobacillus plantarum is a frequently encountered inhabitant of the human intestinal tract, and some strains are marketed as probiotics. Their ability to adhere to mannose residues is a potentially interesting characteristic with regard to proposed probiotic features such as colonization of the intestinal surface and competitive exclusion of pathogens. In this study, the variable capacity of 14 L. plantarum strains to agglutinate Saccharomyces cerevisiae in a mannose-specific manner was determined and subsequently correlated with an L. plantarum WCFS1-based genome-wide genotype database. This led to the identification of four candidate mannose adhesin-encoding genes. Two genes primarily predicted to code for sortase-dependent cell surface proteins displayed a complete gene-trait match. Their involvement in mannose adhesion was corroborated by the finding that a sortase (srtA) mutant of L. plantarum WCFS1 lost the capacity to agglutinate S. cerevisiae. The postulated role of these two candidate genes was investigated by gene-specific deletion and overexpression in L. plantarum WCFS1. Subsequent evaluation of the mannose adhesion capacity of the resulting mutant strains showed that inactivation of one candidate gene (lp_0373) did not affect mannose adhesion properties. In contrast, deletion of the other gene (lp_1229) resulted in a complete loss of yeast agglutination ability, while its overexpression quantitatively enhanced this phenotype. Therefore, this gene was designated to encode the mannose-specific adhesin (Msa; gene name, msa) of L. plantarum. Domain homology analysis of the predicted 1,000-residue Msa protein identified known carbohydrate-binding domains, further supporting its role as a mannose adhesin that is likely to be involved in the interaction of L. plantarum with its host in the intestinal tract.

The Distinct Binding Specificities Exhibited by Enterobacterial Type 1 Fimbriae Are Determined by Their Fimbrial Shafts

Type 1 fimbriae of enterobacteria are heteropolymeric organelles of adhesion composed of FimH, a mannose-binding lectin, and a shaft composed primarily of FimA. We compared the binding activities of recombinant clones expressing type 1 fimbriae from Escherichia coli, Klebsiella pneumoniae, and Salmonella typhimurium for gut and uroepithelial cells and for various soluble mannosylated proteins. Each fimbria was characterized by its capacity to bind particular epithelial cells and to aggregate mannoproteins. However, when each respective FimH subunit was cloned and expressed in the absence of its shaft as a fusion protein with MalE, each FimH bound a wide range of mannose-containing compounds. In addition, we found that expression of FimH on a heterologous fimbrial shaft, e.g. K. pneumoniae FimH on the E. coli fimbrial shaft or vice versa, altered the binding specificity of FimH such that it closely resembled that of the native heterologous type 1 fimbriae. Furthermore, attachment to and invasion of bladder epithelial cells, which were mediated much better by native E. coli type 1 fimbriae compared with native K. pneumoniae type 1 fimbriae, were found to be dependent on the background of the fimbrial shaft (E. coli versus K. pneumoniae) rather than the background of the FimH expressed. Thus, the distinct binding specificities of different enterobacterial type 1 fimbriae cannot be ascribed solely to the primary structure of their respective FimH subunits, but are also modulated by the fimbrial shaft on which each FimH subunit is presented, possibly through conformational constraints imposed on FimH by the fimbrial shaft. The capacity of type 1 fimbrial shafts to modulate the tissue tropism of different enterobacterial species represents a novel function for these highly organized structures.

Molecular structure of adhesin domains in Escherichia coli fimbriae

Crystal structures of FimH, PapG, GafD, and DraE fimbrial adhesin subunits or lectin domains have been resolved. These adhesins bind to different targets and are only distantly related in amino acid sequence. The overall structures of the fimbrial lectins, however, appear similar, suggesting that the fimbrial lectins have diverged from a common scaffold. FimH, PapG and GafD are two-domain structures connected by a flexible linker, and the N-terminal adhesin domains have an elongated beta-barrel jelly roll fold that contains the receptor-binding groove. The adhesin domains differ in disulfide patterns, in size and location of the ligand-binding groove, as well as in mechanism of receptor binding. Minor sequence variations that can be either distant from, near to, or at the ligand-binding groove have profound effects on receptor binding by the fimbriae; this is particularly apparent with FimH. The existing structures give insight into the molecular basis of the diversity in fimbrial lectins.

Escherichia coli K1 RS218 interacts with human brain microvascular endothelial cells via type 1 fimbria bacteria in the fimbriated state

Escherichia coli K1 is a major gram-negative organism causing neonatal meningitis. E. coli K1 binding to and invasion of human brain microvascular endothelial cells (HBMEC) are a prerequisite for E. coli penetration into the central nervous system in vivo. In the present study, we showed using DNA microarray analysis that E. coli K1 associated with HBMEC expressed significantly higher levels of the fim genes compared to nonassociated bacteria. We also showed that E. coli K1 binding to and invasion of HBMEC were significantly decreased with its fimH deletion mutant and type 1 fimbria locked-off mutant, while they were significantly increased with its type 1 fimbria locked-on mutant. E. coli K1 strains associated with HBMEC were predominantly type 1 fimbria phase-on (i.e., fimbriated) bacteria. Taken together, we showed for the first time that type 1 fimbriae play an important role in E. coli K1 binding to and invasion of HBMEC and that type 1 fimbria phase-on E. coli is the major population interacting with HBMEC.