The O75X adhesin of uropathogenic Escherichia coli is a type IV collagen-binding protein

Binding of the extracellular matrix laminin-1 to Clostridioides difficile strains

BACKGROUND

Clostridioides difficile is the most common cause of nosocomial diarrhea associated with antibiotic use. The disease’s symptoms are caused by enterotoxins, but other surface adhesion factors also play a role in the pathogenesis. These adhesins will bind to components of extracellular matrix.

OBJECTIVE

There is a lack of knowledge on MSCRAMM, this work set-out to determine the adhesive properties of several C. difficile ribotypes (027, 133, 135, 014, 012) towards laminin-1 (LMN-1).

METHODS

A binding experiment revealed that different ribotypes have distinct adhesion capabilities. To identify this adhesin, an affinity chromatography column containing LMN-1 was prepared and total protein extracts were analysed using mass spectrometry.

FINDINGS

Strains from ribotypes 012 and 027 had the best adhesion when incubated with glucose supplementations (0.2%, 0.5%, and 1%), while RT135 had a poor adherence. The criteria were not met by RT014 and RT133. In the absence of glucose, there was no adhesion for any ribotype, implying that glucose is required and plays a significant role in adhesion.

MAIN CONCLUSIONS

These findings show that in the presence of glucose, each C. difficile ribotype interacts differently with LMN-1, and the adhesin responsible for recognition could be SlpA protein.

Molecular determinants of surface colonisation in diarrhoeagenic Escherichia coli (DEC): from bacterial adhesion to biofilm formation

Escherichia coli is primarily known as a commensal colonising the gastrointestinal tract of infants very early in life but some strains being responsible for diarrhoea, which can be especially severe in young children. Intestinal pathogenic E. coli include six pathotypes of diarrhoeagenic E. coli (DEC), namely, the (i) enterotoxigenic E. coli, (ii) enteroaggregative E. coli, (iii) enteropathogenic E. coli, (iv) enterohemorragic E. coli, (v) enteroinvasive E. coli and (vi) diffusely adherent E. coli. Prior to human infection, DEC can be found in natural environments, animal reservoirs, food processing environments and contaminated food matrices. From an ecophysiological point of view, DEC thus deal with very different biotopes and biocoenoses all along the food chain. In this context, this review focuses on the wide range of surface molecular determinants acting as surface colonisation factors (SCFs) in DEC. In the first instance, SCFs can be broadly discriminated into (i) extracellular polysaccharides, (ii) extracellular DNA and (iii) surface proteins. Surface proteins constitute the most diverse group of SCFs broadly discriminated into (i) monomeric SCFs, such as autotransporter (AT) adhesins, inverted ATs, heat-resistant agglutinins or some moonlighting proteins, (ii) oligomeric SCFs, namely, the trimeric ATs and (iii) supramolecular SCFs, including flagella and numerous pili, e.g. the injectisome, type 4 pili, curli chaperone-usher pili or conjugative pili. This review also details the gene regulatory network of these numerous SCFs at the various stages as it occurs from pre-transcriptional to post-translocational levels, which remains to be fully elucidated in many cases.

Molecular determinants of disease severity in urinary tract infection

The most common and lethal bacterial pathogens have co-evolved with the host. Pathogens are the aggressors, and the host immune system is responsible for the defence. However, immune responses can also become destructive, and excessive innate immune activation is a major cause of infection-associated morbidity, exemplified by symptomatic urinary tract infections (UTIs), which are caused, in part, by excessive innate immune activation. Severe kidney infections (acute pyelonephritis) are a major cause of morbidity and mortality, and painful infections of the urinary bladder (acute cystitis) can become debilitating in susceptible patients. Disease severity is controlled at specific innate immune checkpoints, and a detailed understanding of their functions is crucial for strategies to counter microbial aggression with novel treatment and prevention measures. One approach is the use of bacterial molecules that reprogramme the innate immune system, accelerating or inhibiting disease processes. A very different outcome is asymptomatic bacteriuria, defined by low host immune responsiveness to bacteria with attenuated virulence. This observation provides the rationale for immunomodulation as a new therapeutic tool to deliberately modify host susceptibility, control the host response and avoid severe disease. The power of innate immunity as an arbitrator of health and disease is also highly relevant for emerging pathogens, including the current COVID-19 pandemic.

S-layer protein 2 of Lactobacillus crispatus 2029, its structural and immunomodulatory characteristics and roles in protective potential of the whole bacteria against foodborne pathogens

We have previously demonstrated that human vaginal Lactobacillus crispatus 2029 (LC2029) strain is highly adhesive to cervicovaginal epithelial cells, exhibits antagonistic activity against genitourinary pathogens and expresses surface-layer protein (Slp). The aims of the present study were elucidation of Slp structural and immunomodulatory characteristics and its roles in protective properties of the whole vaginal LC2029 bacteria against foodborne pathogens. Enteric Caco-2 and colon HT-29 cell lines were used as the in vitro models of the human intestinal epithelial layer. LC2029 strain has two homologous surface-layer (S-layer) genes, slp1 and slp2. Whilst we found no evidence for the expression of slp1 under the growth conditions used, a very high level of expression of the slp2 gene was detected. C-terminal part of the amino sequence of Slp2 protein was found to be highly similar to that of the conserved C-terminal region of SlpA protein of L. crispatus Zj001 isolated from pig intestines and CbsA protein of L. crispatus JCM5810 isolated from chicken intestines, and was substantially variable at the N-terminal and middle regions. The amino acid sequence identity between SlpA and CbsA was as high as 84%, whilst the identity levels of these sequences with that of Slp2 were only 49% and 50% (respectively). LC2029 strain was found to be both acid and bile tolerant. Survival in simulated gastric and intestinal juices of LC2029 cells unable to produce Slp2 was reduced by 2-3 logs. Vaginal L. crispatus 1385 (LC1385) strain not expressing Slp was also very sensitive to gastric and intestinal stresses. Slp2 was found to be non-covalently bound to the surface of the bacterium, acting as an adhesin and facilitating interaction of LC2029 lactobacilli with the host immature or fully differentiated Caco-2 cells, as well as HT-29 cells. No toxicity to or damage of Caco-2 or HT-29 epithelial cells were detected after 24 h of colonization by LC2029 lactobacilli. Both Slp2 protein and LC2029 cells induced NF-kB activation in Caco-2 and HT-29 cells, but did not induce expression of innate immunity mediators Il-8, Il-1β, and TNF-α. Slp2 and LC2029 inhibited Il-8 production in Caco-2 and HT-29 cells induced by MALP-2 and increased production of anti-inflammatory cytokine Il-6. Slp2 inhibited production of CXCL1 and RANTES by Caco-2 cells during differentiation and maturation process within 15 days. Culturing Caco-2 and HT-29 cells in the presence of Slp2 increased adhesion of bifidobacteria BLI-2780 to these enterocytes. Upon binding to Caco-2 and HT-29 cells, Slp2 protein and LC2029 lactobacilli were recognized by toll-like receptors (TLR) 2/6. It was shown that LC2029 strain is a strong co-aggregator of foodborne pathogens Campylobacter jejuni, Salmonella enteritidis, and Escherichia coli O157:H used in this study. The Slp2 was responsible for the ability of LC2029 to co-aggregate these enteropathogens. Slp2 and intact LC2029 lactobacilli inhibited foodborne pathogen-induced activation of caspase-9 and caspase-3 as apoptotic biomarkers in Caco-2 and HT-29 cells. In addition, Slp2 and Slp2-positive LC2029 strain reduced adhesion of tested pathogenic bacteria to Caco-2 and HT-29 cells. Slp2-positive LC2029 strain but not Slp2 alone provided bactericidal effect on foodborne pathogens. These results suggest a range of mechanisms involved in inhibition of growth, viability, and cell-adhesion properties of pathogenic Proteobacteria by the Slp2 producing LC2029, which may be useful in treatment of necrotizing enterocolitis (NEC) in newborns and foodborne infectious diseases in children and adults, increasing the colonization resistance and maintaining the intestinal homeostasis.

A shear stress micromodel of urinary tract infection by the Escherichia coli producing Dr adhesin

In this study, we established a dynamic micromodel of urinary tract infection to analyze the impact of UT-segment-specific urinary outflow on the persistence of E. coli colonization. We found that the adherence of Dr+ E. coli to bladder T24 transitional cells and type IV collagen is maximal at lowest shear stress and is reduced by any increase in flow velocity. The analyzed adherence was effective in the whole spectrum of physiological shear stress and was almost irreversible over the entire range of generated shear force. Once Dr+ E. coli bound to host cells or collagen, they did not detach even in the presence of elevated shear stress or of chloramphenicol, a competitive inhibitor of binding. Investigating the role of epithelial surface architecture, we showed that the presence of budding cells–a model microarchitectural obstacle–promotes colonization of the urinary tract by E. coli. We report a previously undescribed phenomenon of epithelial cell “rolling-shedding” colonization, in which the detached epithelial cells reattach to the underlying cell line through a layer of adherent Dr+ E. coli. This rolling-shedding colonization progressed continuously due to “refilling” induced by the flow-perturbing obstacle. The shear stress of fluid containing free-floating bacteria fueled the rolling, while providing an uninterrupted supply of new bacteria to be trapped by the rolling cell. The progressive rolling allows for transfer of briefly attached bacteria onto the underlying monolayer in a repeating cascading event.

Uropathogenic E. coli (UPEC) equipped with Dr fimbriae are associated with recurrent and chronic urinary tract infections (UTIs). The fimbriae assembled by the chaperone-usher pathway provide strong host-specific adherence which is, however, strongly modulated by the dynamically changing urine flow in the urinary tract (UT). In this paper, we use a dynamic in vitro micro-model of UTI to analyze the UT segment-specific impact of urinary outflow on the persistence and spread of Dr+ E. coli during host colonization. We conclude that the adhesive envelope formed by Dr fimbriae promotes strong and irreversible multivalent adherence of Dr+ E. coli to host receptors under flow conditions. We also observed that budding host cells–a model of any form of epithelial roughness, including carcinogenesis or physical injuries–facilitate the adherence of bacteria at flow conditions typically found in the UT, and our numerical simulations provided a mechanistic explanation for this effect. Finally, we combined the results to propose a rolling-shedding-refilling colonization model that shows how the wash off of detached colonized host cells may provoke a massive spread of UPEC. Our findings shed new light on UTI development and may be instrumental in the development of novel therapeutics.

Pili Assembled by the Chaperone/Usher Pathway in Escherichia coli and Salmonella

Gram-negative bacteria assemble a variety of surface structures, including the hair-like organelles known as pili or fimbriae. Pili typically function in adhesion and mediate interactions with various surfaces, with other bacteria, and with other types of cells such as host cells. The chaperone/usher (CU) pathway assembles a widespread class of adhesive and virulence-associated pili. Pilus biogenesis by the CU pathway requires a dedicated periplasmic chaperone and integral outer membrane protein termed the usher, which forms a multifunctional assembly and secretion platform. This review addresses the molecular and biochemical aspects of the CU pathway in detail, focusing on the type 1 and P pili expressed by uropathogenic Escherichia coli as model systems. We provide an overview of representative CU pili expressed by E. coli and Salmonella, and conclude with a discussion of potential approaches to develop antivirulence therapeutics that interfere with pilus assembly or function.

Pathoadaptive Mutations in Uropathogenic Escherichia coli

Uropathogenic Escherichia coli (UPEC) are opportunistic human pathogens that primarily circulate as part of commensal intestinal microbiota. Though they have the ability to survive and proliferate in various urinary tract compartments, the urinary tract is a transient, occasional habitat for UPEC. Because of this, most of the UPEC traits have originally evolved to serve in intestinal colonization and transmission. Some of these bacterial traits serve as virulence factors - they are critical to or assist in survival of UPEC as pathogens, and the structure and/or function may be specialized for the infection. Other traits could serve as anti-virulence factors - they represent liability in the urinary tract and are under selection to be lost or inactivated during the infection. Inactivation, variation, or other changes of the bacterial genes that increase the pathogen's fitness during the infection are called pathoadaptive mutations. This chapter describes examples of pathoadaptive mutations in UPEC and provides rationale for their further in-depth study.

Probiotic Properties of Lactobacillus crispatus 2,029: Homeostatic Interaction with Cervicovaginal Epithelial Cells and Antagonistic Activity to Genitourinary Pathogens

Lactobacillus crispatus 2029 isolated upon investigation of vaginal lactobacilli of healthy women of reproductive age was selected as a probiotic candidate. The aim of the present study was elucidation of the role of L. crispatus 2029 in resistance of the female reproductive tract to genitourinary pathogens using cervicovaginal epithelial model. Lactobacillus crispatus 2029 has surface layers (S-layers), which completely surround cells as the outermost component of their envelope. S-layers are responsible for the adhesion of lactobacilli on the surface of cervicovaginal epithelial cells. Study of interactions between L. crispatus 2029 and a type IV collagen, a major molecular component of epithelial cell extracellular matrix, showed that 125I-labeled type IV collagen binds to lactobacilli with high affinity (Kd = (8.0 ± 0.7) × 10(-10) M). Lactobacillus crispatus 2029 consistently colonized epithelial cells. There were no toxicity, epithelial damage and apoptosis after 24 h of colonization. Electronic microscope images demonstrated intimate association between L. crispatus 2029 and epithelial cells. Upon binding to epithelial cells, lactobacilli were recognized by toll-like 2/6 receptors. Lactobacillus crispatus induced NF-κB activation in epithelial cells and did not induce expression of innate immunity mediators IL-8, IL-1β, IL-1α and TNF-α. Lactobacillus crispatus 2029 inhibited IL-8 production in epithelial cells induced by MALP-2 and increased production of anti-inflammatory cytokine IL-6, maintaining the homeostasis of female reproductive tract. Lactobacillus crispatus 2029 produced H2O2 and provided wide spectrum of antagonistic activity increasing colonization resistance to urinary tract infections by bacterial vaginosis and vulvovaginal candidiasis associated agents.

Bacterial Surfaces: Front Lines in Host-Pathogen Interaction

All bacteria are bound by at least one membrane that acts as a barrier between the cell's interior and the outside environment. Surface components within and attached to the cell membrane are essential for ensuring that the overall homeostasis of the cell is maintained. However, many surface components of the bacterial cell also have an indispensable role mediating interactions of the bacteria with their immediate environment and as such are essential to the pathogenesis of infectious disease. During the course of an infection, bacterial pathogens will encounter many different ecological niches where environmental conditions such as salinity, temperature, pH, and the availability of nutrients fluctuate. It is the bacterial cell surface that is at the front-line of these host-pathogen interactions often protecting the bacterium from hostile surroundings but at the same time playing a critical role in the adherence to host tissues promoting colonization and subsequent infection. To deal effectively with the changing environments that pathogens may encounter in different ecological niches within the host many of the surface components of the bacterial cell are subject to phenotypic variation resulting in heterogeneous subpopulations of bacteria within the clonal population. This dynamic phenotypic heterogeneity ensures that at least a small fraction of the population will be adapted for a particular circumstance should it arise. Diversity within the clonal population has often been masked by studies on entire bacterial populations where it was often assumed genes were expressed in a uniform manner. This chapter, therefore, aims to highlight the non-uniformity in certain cell surface structures and will discuss the implication of this heterogeneity in bacterial-host interaction. Some of the recent advances in studying bacterial surface structures at the single cell level will also be reviewed.

Pathogenesis of human diffusely adhering Escherichia coli expressing Afa/Dr adhesins (Afa/Dr DAEC): current insights and future challenges

The pathogenicity and clinical pertinence of diffusely adhering Escherichia coli expressing the Afa/Dr adhesins (Afa/Dr DAEC) in urinary tract infections (UTIs) and pregnancy complications are well established. In contrast, the implication of intestinal Afa/Dr DAEC in diarrhea is still under debate. These strains are age dependently involved in diarrhea in children, are apparently not involved in diarrhea in adults, and can also be asymptomatic intestinal microbiota strains in children and adult. This comprehensive review analyzes the epidemiology and diagnosis and highlights recent progress which has improved the understanding of Afa/Dr DAEC pathogenesis. Here, I summarize the roles of Afa/Dr DAEC virulence factors, including Afa/Dr adhesins, flagella, Sat toxin, and pks island products, in the development of specific mechanisms of pathogenicity. In intestinal epithelial polarized cells, the Afa/Dr adhesins trigger cell membrane receptor clustering and activation of the linked cell signaling pathways, promote structural and functional cell lesions and injuries in intestinal barrier, induce proinflammatory responses, create angiogenesis, instigate epithelial-mesenchymal transition-like events, and lead to pks-dependent DNA damage. UTI-associated Afa/Dr DAEC strains, following adhesin-membrane receptor cell interactions and activation of associated lipid raft-dependent cell signaling pathways, internalize in a microtubule-dependent manner within urinary tract epithelial cells, develop a particular intracellular lifestyle, and trigger a toxin-dependent cell detachment. In response to Afa/Dr DAEC infection, the host epithelial cells generate antibacterial defense responses. Finally, I discuss a hypothetical role of intestinal Afa/Dr DAEC strains that can act as "silent pathogens" with the capacity to emerge as "pathobionts" for the development of inflammatory bowel disease and intestinal carcinogenesis.

Pilicides inhibit the FGL chaperone/usher assisted biogenesis of the Dr fimbrial polyadhesin from uropathogenic Escherichia coli

BACKGROUND

The global spread of bacterial resistance has given rise to a growing interest in new anti-bacterial agents with a new strategy of action. Pilicides are derivatives of ring-fused 2-pyridones which block the formation of the pili/fimbriae crucial to bacterial pathogenesis. They impair by means of a chaperone-usher pathway conserved in the Gram-negative bacteria of adhesive structures biogenesis. Pili/fimbriae of this type belong to two subfamilies, FGS and FGL, which differ in the details of their assembly mechanism. The data published to date have shown that pilicides inhibit biogenesis of type 1 and P pili of the FGS type which are encoded by uropathogenic E. coli strains.

RESULTS

We evaluated the anti-bacterial activity of literature pilicides as blockers of the assembly of a model example of FGL-type adhesive structures--the Dr fimbriae encoded by a dra gene cluster of uropathogenic Escherichia coli strains. In comparison to the strain grown without pilicide, the Dr⁺ bacteria cultivated in the presence of the 3.5 mM concentration of pilicides resulted in a reduction of 75 to 87% in the adherence properties to CHO cells expressing Dr fimbrial DAF receptor protein. Using quantitative assays, we determined the amount of Dr fimbriae in the bacteria cultivated in the presence of 3.5 mM of pilicides to be reduced by 75 to 81%. The inhibition effect of pilicides is concentration dependent, which is a crucial property for their use as potential anti-bacterial agents. The data presented in this article indicate that pilicides in mM concentration effectively inhibit the adherence of Dr⁺ bacteria to the host cells--the crucial, initial step in bacterial pathogenesis.

CONCLUSIONS

Structural analysis of the DraB chaperone clearly showed it to be a model of the FGL subfamily of chaperones. This permits us to conclude that analyzed pilicides in mM concentration are effective inhibitors of the assembly of adhesins belonging to the Dr family, and more speculatively, of other FGL-type adhesive organelles. The presented data and those published so far permit to speculate that based on the conservation of chaperone-usher pathway in Gram-negative bacteria , the pilicides are potential anti-bacterial agents with activity against numerous pathogens, the virulence of which is dependent on the adhesive structures of the chaperone-usher type.

Distribution of uropathogenic virulence genes in Escherichia coli isolated from patients with urinary tract infection

BACKGROUND

Escherichia coli is the predominant pathogen causing urinary tract infection (UTI), the most common bacterial infectious disease encountered in clinical practice, accounting for significant morbidity and high medical costs. The severity of UTI produced by E. coli is due to the expression of a wide spectrum of virulence factors. In this study we evaluated the role of E. coli virulence determinants in the pathogenesis of UTI.

METHODS

A total of 90 uropathogenic E. coli strains were screened by PCR for the prevalence of seven virulence genes encoding type 1 fimbriae (fimH), pili associated with pyelonephritis (pap), S and F1C fimbriae (sfa and foc), afimbrial adhesins (afa), cytotoxic necrotizing factor (cnf), hemolysin (hly), and aerobactin (aer).

RESULTS

The prevalence of genes coding for fimbrial adhesive systems was 68% for fimH, 41% for pap, and 34% for sfa/foc. The operons coding for afa afimbrial adhesins were identified in 20% of strains. The hly and cnf genes coding for toxins were amplified in 19% and 3% of strains, respectively. A prevalence of 52% was found for the aer gene. The various combinations of detected genes were designated as virulence patterns. The strains isolated from hospitalized patients displayed a great diversity of gene associations compared to those isolated from ambulatory patients.

CONCLUSIONS

Our study showed that investigation of the bacterial pathogenicity associated with UTI may contribute to a better medical intervention.

Crystal structure of the MrkD1P receptor binding domain of Klebsiella pneumoniae and identification of the human collagen V binding interface

Klebsiella species are members of the family enterobacteriaceae, opportunistic pathogens that are among the eight most prevalent infectious agents in hospitals. Among other virulence factors in Klebsiella, type 3 pili exhibit a unique binding pattern in the human kidney via interaction of two MrkD adhesion variants 1C1 and 1P to type IV and/or V collagen. However, very little is known about the nature of this recognition. Here we present the crystal structure of the plasmid born MrkD1P receptor domain (MrkDrd). The structure reveals a jelly-roll β-barrel fold comprising 17 β-strands very similar to the receptor domain of GafD, the tip adhesin from the F17 pilus that recognizes n-acetyl-d-glucosamine (GlcNAc). Analysis of collagen V binding of different MrkD1P mutants revealed that two regions were responsible for its binding: a pocket, that aligns approximately with the GlcNAc binding pocket of GafD involving residues R105 and Y155, and a transversally oriented patch that spans strands β2a, β9b and β6 including residues V49, T52, V91, R102 and I136. Taken together, these data provide structural and functional insights on MrkD1P recognition of host cells, providing a tool for future development of rationally designed drugs with the prospect of blocking Klebsiella adhesion to collagen V.

Human pathogens utilize host extracellular matrix proteins laminin and collagen for adhesion and invasion of the host

Laminin (Ln) and collagen are multifunctional glycoproteins that play an important role in cellular morphogenesis, cell signalling, tissue repair and cell migration. These proteins are ubiquitously present in tissues as a part of the basement membrane (BM), constitute a protective layer around blood capillaries and are included in the extracellular matrix (ECM). As a component of BMs, both Lns and collagen(s), thus function as major mechanical containment molecules that protect tissues from pathogens. Invasive pathogens breach the basal lamina and degrade ECM proteins of interstitial spaces and connective tissues using various ECM-degrading proteases or surface-bound plasminogen and matrix metalloproteinases recruited from the host. Most pathogens associated with the respiratory, gastrointestinal, or urogenital tracts, as well as with the central nervous system or the skin, have the capacity to bind and degrade Lns and collagen(s) in order to adhere to and invade host tissues. In this review, we focus on the adaptability of various pathogens to utilize these ECM proteins as enhancers for adhesion to host tissues or as a targets for degradation in order to breach the cellular barriers. The major pathogens discussed are Streptococcus, Staphylococcus, Pseudomonas, Salmonella, Yersinia, Treponema, Mycobacterium, Clostridium, Listeria, Porphyromonas and Haemophilus; Candida, Aspergillus, Pneumocystis, Cryptococcus and Coccidioides; Acanthamoeba, Trypanosoma and Trichomonas; retrovirus and papilloma virus.

Preventing urinary tract infection: progress toward an effective Escherichia coli vaccine

Uncomplicated urinary tract infections (UTIs) are common, with nearly half of all women experiencing at least one UTI in their lifetime. This high frequency of infection results in huge annual economic costs, decreased workforce productivity and high patient morbidity. At least 80% of these infections are caused by uropathogenic Escherichia coli (UPEC). UPEC can reside side by side with commensal strains in the gastrointestinal tract and gain access to the bladder via colonization of the urethra. Antibiotics represent the current standard treatment for UTI; however, even after treatment, patients frequently suffer from recurrent infection with the same or different strains. In addition, successful long-term treatment has been complicated by a rise in both the number of antibiotic-resistant strains and the prevalence of antibiotic-resistance mechanisms. As a result, preventative approaches to UTI, such as vaccination, have been sought. This review summarizes recent advances in UPEC vaccine development and outlines future directions for the field.

Adhesive polypeptides of Staphylococcus aureus identified using a novel secretion library technique in Escherichia coli

BACKGROUND

Bacterial adhesive proteins, called adhesins, are frequently the decisive factor in initiation of a bacterial infection. Characterization of such molecules is crucial for the understanding of bacterial pathogenesis, design of vaccines and development of antibacterial drugs. Because adhesins are frequently difficult to express, their characterization has often been hampered. Alternative expression methods developed for the analysis of adhesins, e.g. surface display techniques, suffer from various drawbacks and reports on high-level extracellular secretion of heterologous proteins in Gram-negative bacteria are scarce. These expression techniques are currently a field of active research. The purpose of the current study was to construct a convenient, new technique for identification of unknown bacterial adhesive polypeptides directly from the growth medium of the Escherichia coli host and to identify novel proteinaceous adhesins of the model organism Staphylococcus aureus.

RESULTS

Randomly fragmented chromosomal DNA of S. aureus was cloned into a unique restriction site of our expression vector, which facilitates secretion of foreign FLAG-tagged polypeptides into the growth medium of E. coli ΔfliCΔfliD, to generate a library of 1663 clones expressing FLAG-tagged polypeptides. Sequence and bioinformatics analyses showed that in our example, the library covered approximately 32% of the S. aureus proteome. Polypeptides from the growth medium of the library clones were screened for binding to a selection of S. aureus target molecules and adhesive fragments of known staphylococcal adhesins (e.g coagulase and fibronectin-binding protein A) as well as polypeptides of novel function (e.g. a universal stress protein and phosphoribosylamino-imidazole carboxylase ATPase subunit) were detected. The results were further validated using purified His-tagged recombinant proteins of the corresponding fragments in enzyme-linked immunoassay and surface plasmon resonance analysis.

CONCLUSIONS

A new technique for identification of unknown bacterial adhesive polypeptides was constructed. Application of the method on S. aureus allowed us to identify three known adhesins and in addition, five new polypeptides binding to human plasma and extracellular matrix proteins. The method, here used on S. aureus, is convenient due to the use of soluble proteins from the growth medium and can in principle be applied to any bacterial species of interest.

Analysis of the unique structural and physicochemical properties of the DraD/AfaD invasin in the context of its belonging to the family of chaperone/usher type fimbrial subunits

Background

DraD invasin encoded by the dra operon possesses a classical structure characteristic to fimbrial subunits of the chaperone/usher type. The Ig-fold of the DraD possesses two major characteristics distinguishing it from the family of fimbrial subunits: 1) a distortion of the β-barrel structure in the region of the acceptor cleft, demonstrated by a disturbance of the main-chain hydrogen bonds network, and 2) an unusually located disulfide bond connecting B and F strands - the localization exclusively observed in the subfamily of DraD/AfaD-type subunits.

Results

To evaluate the influence of the DraD-sc specific structural features on its stability and mechanism of thermal denaturation, a series of DSC and FT-IR denaturation experiments were performed giving following conclusions. 1) The DraD-sc is characterized by a low stability (standard Gibbs free energy and enthalpy of unfolding of 18.4 ±1.4 kJ mol^-1 and 131 ±25 kJ mol^-1, respectively) that contrasts strongly with almost infinite stability of the described previously DraE-sc fimbrial protein. 2) The DraD-sc unfolds thermally according to the two state equilibrium model, in contrast to the irreversible kinetically controlled transition of the DraE-sc. 3) The DraD specific disulfide bond is crucial at the folding stage and has little stability effect in the mature protein.

Conclusions

Data published so far emphasize unique biological properties of the DraD invasin as fimbrial subunit: a chaperone independent folding, an usher independent surface localization and the possibility to exist in two forms: as unbound subunits and as loosely bound at fimbrial tip.

Presented calorimetric and FT-IR stability data combined with structural correlations has underlined that the DraD invasin is also characterized by unique physicochemical and structural attributes in the context of its belonging to the family of fimbrial subunits.

Mapping structural landmarks, ligand binding sites, and missense mutations to the collagen IV heterotrimers predicts major functional domains, novel interactions, and variation in phenotypes in inherited diseases affecting basement membranes

Collagen IV is the major protein found in basement membranes. It comprises three heterotrimers (α1α1α2, α3α4α5, and α5α5α6) that form distinct networks, and are responsible for membrane strength and integrity.We constructed linear maps of the collagen IV heterotrimers ("interactomes") that indicated major structural landmarks, known and predicted ligand-binding sites, and missense mutations, in order to identify functional and disease-associated domains, potential interactions between ligands, and genotype–phenotype relationships. The maps documented more than 30 known ligand-binding sites as well as motifs for integrins, heparin, von Willebrand factor (VWF), decorin, and bone morphogenetic protein (BMP). They predicted functional domains for angiogenesis and haemostasis, and disease domains for autoimmunity, tumor growth and inhibition, infection, and glycation. Cooperative ligand interactions were indicated by binding site proximity, for example, between integrins, matrix metalloproteinases, and heparin. The maps indicated that mutations affecting major ligand-binding sites, for example, for Von Hippel Lindau (VHL) protein in the α1 chain or integrins in the α5 chain, resulted in distinctive phenotypes (Hereditary Angiopathy, Nephropathy, Aneurysms, and muscle Cramps [HANAC] syndrome, and early-onset Alport syndrome, respectively). These maps further our understanding of basement membrane biology and disease, and suggest novel membrane interactions, functions, and therapeutic targets.

Host-pathogen interactions in urinary tract infection

The urinary tract is a common site of bacterial infections; nearly half of all women experience at least one urinary tract infection (UTI) during their lifetime. These infections are classified based on the condition of the host. Uncomplicated infections affect otherwise healthy individuals and are most commonly caused by uropathogenic Escherichia coli, whereas complicated infections affect patients with underlying difficulties, such as a urinary tract abnormality or catheterization, and are commonly caused by species such as Proteus mirabilis. Virulence and fitness factors produced by both pathogens include fimbriae, toxins, flagella, iron acquisition systems, and proteins that function in immune evasion. Additional factors that contribute to infection include the formation of intracellular bacterial communities by E. coli and the production of urease by P. mirabilis, which can result in urinary stone formation. Innate immune responses are induced or mediated by pattern recognition receptors, antimicrobial peptides, and neutrophils. The adaptive immune response to UTI is less well understood. Host factors TLR4 and CXCR1 are implicated in disease outcome and susceptibility, respectively. Low levels of TLR4 are associated with asymptomatic bacteriuria while low levels of CXCR1 are associated with increased incidence of acute pyelonephritis. Current research is focused on the identification of additional virulence factors and therapeutic or prophylactic targets that might be used in the generation of vaccines against both uropathogens.

A Collagen-Binding S-Layer Protein in Lactobacillus crispatus

Two S-layer-expressing strains, Lactobacillus crispatus JCM 5810 and Lactobacillus acidophilus JCM 1132, were assessed for adherence to proteins of the mammalian extracellular matrix. L. crispatus JCM 5810 adhered efficiently to immobilized type IV and I collagens, laminin, and, with a lower affinity, to type V collagen and fibronectin. Strain JCM 1132 did not exhibit detectable adhesiveness. Within the fibronectin molecule, JCM 5810 recognized the 120-kDa cell-binding fragment of the protein, while no bacterial adhesion to the amino-terminal 30-kDa or the gelatin-binding 40-kDa fragment was detected. JCM 5810 but not JCM 1132 also bound (sup125)I-labelled soluble type IV collagen, and this binding was efficiently inhibited by unlabelled type IV and I collagens and less efficiently by type V collagen, but not by laminin or fibronectin. L. crispatus JCM 5810 but not L. acidophilus JCM 1132 also adhered to Matrigel, a reconstituted basement membrane preparation from mouse sarcoma cells, as well as to the extracellular matrix prepared from human Intestine 407 cells. S-layers from both strains were extracted with 2 M guanidine hydrochloride, separated by electrophoresis, and transferred to nitrocellulose sheets. The S-layer protein from JCM 5810 bound (sup125)I-labelled type IV collagen, whereas no binding was seen with the S-layer protein from JCM 1132. Binding of (sup125)I-collagen IV to the JCM 5810 S-layer protein was effectively inhibited by unlabelled type I and IV collagens but not by type V collagen, laminin, or fibronectin. It was concluded that L. crispatus JCM 5810 has the capacity to adhere to human subintestinal extracellular matrix via a collagen-binding S-layer.

Ail binding to fibronectin facilitates Yersinia pestis binding to host cells and Yop delivery

Yersinia pestis, the causative agent of plague, evades host immune responses and rapidly causes disease. The Y. pestis adhesin Ail mediates host cell binding and is critical for Yop delivery. To identify the Ail receptor(s), Ail was purified following overexpression in Escherichia coli. Ail bound specifically to fibronectin, an extracellular matrix protein with the potential to act as a bridge between Ail and host cells. Ail expressed by E. coli also mediated binding to purified fibronectin, and Ail-mediated E. coli adhesion to host cells was dependent on fibronectin. Ail expressed by Y. pestis bound purified fibronectin, as did the Y. pestis adhesin plasminogen activator (Pla). However, a KIM5 Delta ail mutant had decreased binding to host cells, while a KIM5 Delta pla mutant had no significant defect in adhesion. Furthermore, treatment with antifibronectin antibodies decreased Ail-mediated adhesion by KIM5 and the KIM5 Delta pla mutant, indicating that the Ail-fibronectin interaction was important for cell binding. Finally, antifibronectin antibodies inhibited the KIM5-mediated cytotoxicity of host cells in an Ail-dependent fashion. These data indicate that Ail is a key adhesin that mediates binding to host cells through interaction with fibronectin on the surface of host cells, and this interaction is important for Yop delivery by Y. pestis.

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.

Uropathogenic Escherichia coli

The urinary tract is among the most common sites of bacterial infection, and Escherichia coli is by far the most common species infecting this site. Individuals at high risk for symptomatic urinary tract infection (UTI) include neonates, preschool girls, sexually active women, and elderly women and men. E. coli that cause the majority of UTIs are thought to represent only a subset of the strains that colonize the colon. E. coli strains that cause UTIs are termed uropathogenic E. coli (UPEC). In general, UPEC strains differ from commensal E. coli strains in that the former possess extragenetic material, often on pathogenicity-associated islands (PAIs), which code for gene products that may contribute to bacterial pathogenesis. Some of these genes allow UPEC to express determinants that are proposed to play roles in disease. These factors include hemolysins, secreted proteins, specific lipopolysaccharide and capsule types, iron acquisition systems, and fimbrial adhesions. The current dogma of bacterial pathogenesis identifies adherence, colonization, avoidance of host defenses, and damage to host tissues as events vital for achieving bacterial virulence. These considerations, along with analysis of the E. coli CFT073, UTI89, and 536 genomes and efforts to identify novel virulence genes should advance the field significantly and allow for the development of a comprehensive model of pathogenesis for uropathogenic E. coli.Further study of the adaptive immune response to UTI will be especially critical to refine our understanding and treatment of recurrent infections and to develop vaccines.

A structural study of the interaction between the Dr haemagglutinin DraE and derivatives of chloramphenicol

Dr adhesins are expressed on the surface of uropathogenic and diffusely adherent strains of Escherichia coli. The major adhesin subunit (DraE/AfaE) of these organelles mediates attachment of the bacterium to the surface of the host cell and possibly intracellular invasion through its recognition of the complement regulator decay-accelerating factor (DAF) and/or members of the carcinoembryonic antigen (CEA) family. The adhesin subunit of the Dr haemagglutinin, a Dr-family member, additionally binds type IV collagen and is inhibited in all its receptor interactions by the antibiotic chloramphenicol (CLM). In this study, previous structural work is built upon by reporting the X-ray structures of DraE bound to two chloramphenicol derivatives: chloramphenicol succinate (CLS) and bromamphenicol (BRM). The CLS structure demonstrates that acylation of the 3-hydroxyl group of CLM with succinyl does not significantly perturb the mode of binding, while the BRM structure implies that the binding pocket is able to accommodate bulkier substituents on the N-acyl group. It is concluded that modifications of the 3-hydroxyl group would generate a potent Dr haemagglutinin inhibitor that would not cause the toxic side effects that are associated with the normal bacteriostatic activity of CLM.

Host protein binding and adhesive properties of H6 and H7 flagella of attaching and effacing Escherichia coli

It had been suggested that the flagella of enteropathogenic Escherichia coli (EPEC) and enterohemorrhagic E. coli (EHEC) might contribute to host colonization. In this study, we set out to investigate the adhesive properties of H7 and H6 flagella. We studied the abilities of EHEC EDL933 (O157:H7) and EPEC E2348/69 (O127:H6) flagella to bind to bovine mucus, host proteins such as mucins, and extracellular matrix proteins. Through several approaches, we found that H6 and H7 flagella and their flagellin monomers bind to mucins I and II and to freshly isolated bovine mucus. A genetic approach showed that EHEC and EPEC fliC deletion mutants were significantly less adherent to bovine intestinal tissue than the parental wild-type strains. In addition, we found that EPEC bacteria and H6 flagella, but not EHEC, bound largely, in a dose-dependent manner, to collagen and to a lesser extent to laminin and fibronectin. We also report that EHEC O157:H7 strains agglutinate rabbit red blood cells via their flagella, a heretofore unknown phenotype in this pathogroup. Collectively, our data demonstrate that the H6 and H7 flagella possess adhesive properties, particularly the ability to bind mucins, that may contribute to colonization of mucosal surfaces.

FGL chaperone-assembled fimbrial polyadhesins: anti-immune armament of Gram-negative bacterial pathogens

This review summarizes the current knowledge on the structure, function, assembly, and biomedical applications of the family of adhesive fimbrial organelles assembled on the surface of Gram-negative pathogens via the FGL chaperone/usher pathway. Recent studies revealed the unique structural and functional properties of these organelles, distinguishing them from a related family, FGS chaperone-assembled adhesive pili. The FGL chaperone-assembled organelles consist of linear polymers of one or two types of protein subunits, each possessing one or two independent adhesive sites specific to different host cell receptors. This structural organization enables these fimbrial organelles to function as polyadhesins. Fimbrial polyadhesins may ensure polyvalent fastening of bacteria to the host cells, aggregating their receptors and triggering subversive signals that allow pathogens to evade immune defense. The FGL chaperone-assembled fimbrial polyadhesins are attractive targets for vaccine and drug design.

Selection for functional diversity drives accumulation of point mutations in Dr adhesins of Escherichia coli

Immune escape is considered to be the driving force behind structural variability of major antigens on the surface of bacterial pathogens, such as fimbriae. In the Dr family of Escherichia coli adhesins, structural and adhesive functions are carried out by the same subunit. Dr adhesins have been shown to bind decay-accelerating factor (DAF), collagen IV, and carcinoembryonic antigen-related cell adhesion molecules (CEACAMs). We show that genes encoding Dr adhesins from 100 E. coli strains form eight structural groups with a high level of amino acid sequence diversity between them. However, genes comprising each group differ from each other by only a small number of point mutations. Out of 66 polymorphisms identified within the groups, only three were synonymous mutations, indicating strong positive selection for amino acid replacements. Functional analysis of intragroup variants comprising the Dr haemagglutinin (DraE) group revealed that the point mutations result in distinctly different binding phenotypes, with a tendency of increased affinity to DAF, decreased sensitivity of DAF binding to inhibition by chloramphenicol, and loss of binding capability to collagen, CEACAM3 and CEACAM6. Thus, variability by point mutation of major antigenic proteins on the bacterial surface can be a signature of selection for functional modification.

Collagen binding protein Mip enables Legionella pneumophila to transmigrate through a barrier of NCI-H292 lung epithelial cells and extracellular matrix

Guinea pigs are highly susceptible to Legionella pneumophila infection and therefore have been the preferred animal model for studies of legionellosis. In this study guinea pig infections revealed that the Legionella virulence factor Mip (macrophage infectivity potentiator) contributes to the bacterial dissemination within the lung tissue and the spread of Legionella to the spleen. Histopathology of infected animals, binding assays with components of the extracellular matrix (ECM), bacterial transmigration experiments across an artificial lung epithelium barrier, inhibitor studies and ECM degradation assays were used to elucidate the underlying mechanism of the in vivo observation. The Mip protein, which belongs to the enzyme family of FK506-binding proteins (FKBP), was shown to bind to the ECM protein collagen (type I, II, III, IV, V, VI). Transwell assays with L. pneumophila and recombinant Escherichia coli HB101 strains revealed that Mip enables these bacteria to transmigrate across a barrier of NCI-H292 lung epithelial cells and ECM (NCI-H292/ECM barrier). Mip-specific monoclonal antibodies and the immunosuppressants rapamycin and FK506, which inhibit the peptidyl prolyl cis/trans isomerase (PPIase) activity of Mip, were able to inhibit this transmigration. By using protease inhibitors we found that the penetration of the NCI-H292/ECM barrier additionally requires a serine protease activity. Degradation assays with (35)S-labelled ECM proteins supported the finding of a concerted action of Mip and a serine protease. The described synergism between the activity of the collagen binding Mip protein and the serine protease activity represents an entirely new mechanism for bacterial penetration of the lung epithelial barrier and has implications for other prokaryotic and eukaryotic pathogens.

Adhesive properties of the purified plasminogen activator Pla ofYersinia pestis

The beta-barrel outer membrane protease Pla from Yersinia pestis is an important virulence factor in plague and enables initiation of the bubonic plague. Pla is a multifunctional protease whose expression also enhances bacterial adherence to extracellular matrix. It has remained uncertain whether the increase in cellular adhesiveness results from modification of the bacterial surface by Pla, or whether the Pla molecule is an adhesin. Pla was purified as a His6-fusion protein from Escherichia coli and reconstituted with lipopolysaccharide to an enzymatically active form. Purified His6-Pla was coated onto fluorescent micro-particles (FMPs) that expressed plasminogen activity. Pla-coated FMPs also bound to laminin and to reconstituted basement membrane (Matrigel) immobilized on permanox slides, whereas only poor activity was seen with lipopolysaccharide-coated FMPs or bovine serum albumin-coated FMPs. The results show that the Pla molecule has intrinsic adhesive properties and that purified transmembrane proteins coated onto FMPs can be used for functional assays.

Diffusely adherent Escherichia coli strains expressing Afa/Dr adhesins (Afa/Dr DAEC): hitherto unrecognized pathogens

Diffusely adherent Escherichia coli (DAEC) strains are currently considered to constitute a putative sixth group of diarrheagenic E. coli. However, on the basis of their diffuse adherence to HEp-2 and HeLa cells, the detection of afa/dra/daa-related operons encoding this adherence phenotype, and the mobilization of decay-accelerating factor, both commensal and pathogenic strains can be classified as Afa/Dr DAEC isolates. Furthermore, strains associated with diarrheal diseases and strains causing extra-intestinal infections can also be identified as Afa/Dr DAEC strains. Although several cell signaling events that occur after epithelial cells have been infected by Afa/Dr DAEC have been reported, the pathophysiological processes that allow intestinal and extra-intestinal infections to develop are not fully understood. This review focuses on the genetic organization of the afa/dra/daa-related operons and on the virulence factors that trigger cellular responses, some of which are deleterious for the host cells. Finally, this review suggests future lines of research that could help to elucidate these questions.

Adhesins of Diffusely Adherent and Enteroaggregative Escherichia coli

Epidemiological studies have implicated enteroaggregative Escherichia coli (EAEC) strains in acute and persistent diarrhea in children, in food-borne diarrhea outbreaks, and in traveler's diarrhea, and this group is recognized as an emerging pathotype of enteric disease. Diffusely adherent E. coli (DAEC) have been implicated as a cause of diarrhea, especially in children more than 2 years old, in both developing and developed countries. Although EAEC and DAEC strains appear to have different molecular equipment for attachment to host cell surfaces, identification and characterization of the gene clusters encoding adherence evidenced close relatedness between those determinants most frequently detected in isolates belonging to these two pathotypes of diarrheagenic E. coli. DAEC strains are a heterogeneous group of E. coli isolates, many of which express the related so-called Dr adhesins. The single designation is based on the identification of one similar cellular receptor for all these proteins. Although structurally different, they all recognize the Dr human blood group antigen on the decay-accelerating factor (DAF or CD55). These adhesins are encoded by a family of closely related operons, the first characterized and sequenced being the afa operon. Consequently, it has been suggested that this group of DAEC strains producing such adhesins be named the Afa/Dr DAEC family. Three distinct but closely related gene clusters coding for phenotypically and morphologically distinct aggregative adherence fimbriae (AAF) have been characterized. In each case, electron microscopy revealed that bacterial surfaces were surrounded by long, relatively flexible fimbrial 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.

A surface-exposed DraD protein of uropathogenic Escherichia coli bearing Dr fimbriae may be expressed and secreted independently from DraC usher and DraE adhesin

The dra gene cluster, expressed by uropathogenic Escherichia coli strains, determines bacterial attachment and invasion. The Dr fimbrial structures formed at the bacterial cell surface are composed of DraE subunits. The Dr fimbriae-coding cluster contains six open reading frames – draA, draB, draC, draD, draP and draE – among which the draE gene encodes the structural fimbrial subunit DraE. Very little is known about E. coli surface expression of the draD gene product. The expression of DraD and its role in the biogenesis of Dr fimbriae were determined by constructing mutants in the dra operon and by immunoblot and immunofluorescence experiments. In this study, DraD was found to be a surface-exposed protein. The expression of DraD was independent of the DraC usher and DraE fimbrial subunits. Polymerization of DraE fimbrial subunits into fimbrial structures did not require expression of the DraD protein.

Pathogenesis of Afa/Dr diffusely adhering Escherichia coli

Over the last few years, dramatic increases in our knowledge about diffusely adhering Escherichia coli (DAEC) pathogenesis have taken place. The typical class of DAEC includes E. coli strains harboring AfaE-I, AfaE-II, AfaE-III, AfaE-V, Dr, Dr-II, F1845, and NFA-I adhesins (Afa/Dr DAEC); these strains (i) have an identical genetic organization and (ii) allow binding to human decay-accelerating factor (DAF) (Afa/Dr(DAF) subclass) or carcinoembryonic antigen (CEA) (Afa/Dr(CEA) subclass). The atypical class of DAEC includes two subclasses of strains; the atypical subclass 1 includes E. coli strains that express AfaE-VII, AfaE-VIII, AAF-I, AAF-II, and AAF-III adhesins, which (i) have an identical genetic organization and (ii) do not bind to human DAF, and the atypical subclass 2 includes E. coli strains that harbor Afa/Dr adhesins or others adhesins promoting diffuse adhesion, together with pathogenicity islands such as the LEE pathogenicity island (DA-EPEC). In this review, the focus is on Afa/Dr DAEC strains that have been found to be associated with urinary tract infections and with enteric infection. The review aims to provide a broad overview and update of the virulence aspects of these intriguing pathogens. Epidemiological studies, diagnostic techniques, characteristic molecular features of Afa/Dr operons, and the respective role of Afa/Dr adhesins and invasins in pathogenesis are described. Following the recognition of membrane-bound receptors, including type IV collagen, DAF, CEACAM1, CEA, and CEACAM6, by Afa/Dr adhesins, activation of signal transduction pathways leads to structural and functional injuries at brush border and junctional domains and to proinflammatory responses in polarized intestinal cells. In addition, uropathogenic Afa/Dr DAEC strains, following recognition of beta(1) integrin as a receptor, enter epithelial cells by a zipper-like, raft- and microtubule-dependent mechanism. Finally, the presence of other, unknown virulence factors and the way that an Afa/Dr DAEC strain emerges from the human intestinal microbiota as a "silent pathogen" are discussed.

Covert operations of uropathogenic Escherichia coli within the urinary tract

Entry into host cells is required for many bacterial pathogens to effectively disseminate within a host, avoid immune detection and cause disease. In recent years, many ostensibly extracellular bacteria have been shown to act as opportunistic intracellular pathogens. Among these are strains of uropathogenic Escherichia coli (UPEC), the primary causative agents of urinary tract infections (UTIs). UPEC are able to transiently invade, survive and multiply within the host cells and tissues constituting the urinary tract. Invasion of host cells by UPEC is promoted independently by distinct virulence factors, including cytotoxic necrotizing factor, Afa/Dr adhesins, and type 1 pili. Here we review the diverse mechanisms and consequences of host cell invasion by UPEC, focusing also on the impact of these processes on the persistence and recurrence of UTIs.

Entamoeba histolytica: cDNAs cloned as 30kDa collagen-binding proteins (CBP) belong to an antioxidant molecule family. Protection of hamsters from amoebic liver abscess by immunization with recombinant CBP

A cDNA expression library of Entamoeba histolytica was screened with antiserum to native amoebic collagen binding proteins (CBPs), and two clones C13 and C7 which partially encode for the 30 kDa CBP were obtained. The sequenced clones were 90% homologous. C7 had a 69 bp deletion at the 5' end that is present in C13 and encodes for a Glu-Cys-Lys rich region and a four amino acids repeat (Glu-Lys-Glu-Cys). Purified fusion proteins from these cDNA clones were able to bind native type I collagen gels in a pH, calcium, ionic strength, and temperature dependent way. The binding of pgtC13 to collagen gel was time and temperature stable, while pgtC7 binding was not, suggesting that the deleted region in C7 is important for the binding. The clones reported here partially encode a 30 kDa CBP that also belong to an antioxidant molecule family. We demonstrated that the fusion protein pgtC13 is immunogenic and partially protective as a subunit vaccine in the hamster model of amoebic liver abscess.

High Resolution Studies of the Afa/Dr Adhesin DraE and Its Interaction with Chloramphenicol

Pathogenic Escherichia coli expressing Afa/Dr adhesins are able to cause both urinary tract and diarrheal infections. The Afa/Dr adhesins confer adherence to epithelial cells via interactions with the human complement regulating protein, decay accelerating factor (DAF or CD55). Two of the Afa/Dr adhesions, AfaE-III and DraE, differ from each other by only three residues but are reported to have several different properties. One such difference is disruption of the interaction between DraE and CD55 by chloramphenicol, whereas binding of AfaE-III to CD55 is unaffected. Here we present a crystal structure of a strand-swapped trimer of wild type DraE. We also present a crystal structure of this trimer in complex with chloramphenicol, as well as NMR data supporting the binding position of chloramphenicol within the crystal. The crystal structure reveals the precise atomic basis for the sensitivity of DraE-CD55 binding to chloramphenicol and demonstrates that in contrast to other chloramphenicol-protein complexes, drug binding is mediated via recognition of the chlorine "tail" rather than via intercalation of the benzene rings into a hydrophobic pocket.

Adherence of Actinobacillus pleuropneumoniae to swine-lung collagen

Actinobacillus pleuropneumoniae serotype 1 adhered to immobilized swine-lung collagen. Bacteria bound to collagen type I, III, IV and V. At 5 min incubation, 30 % of bacteria adhered to collagen, reaching saturation in around 90 min. Treatment of bacteria with divalent-metal chelators diminished their attachment to collagen, and Ca(2+) but not Mg(2+) increased it, suggesting Ca(2+) dependence for adherence. Proteolytic enzymes drastically reduced bacterial adherence to collagen, showing that binding involved bacterial surface proteins. Porcine fibrinogen, haemoglobin and gelatin partially reduced collagen adhesion. A 60 kDa outer-membrane protein of A. pleuropneumoniae recognized the swine collagens by overlay. This membrane protein was apparently involved in adhesion to collagen and fibrinogen, but not to fibronectin and laminin. Antibodies against the 60 kDa protein inhibited the adhesion to collagen by 70 %, whereas pig convalescent-phase antibodies inhibited it by only 40 %. Serotypes 1 and 7 were the most adherent to pig collagen (taken as 100 %); serotypes 6 and 11 were the lowest (approximately 50 %), and neither showed the 60 kDa adhesin to biotinylated collagens. By negative staining, cells were observed initially to associate with collagen fibres in a polar manner, and the adhesin was detected on the bacterial surface. The results suggest that swine-lung collagen is an important target for A. pleuropneumoniae colonization and spreading, and that the attachment to this protein could play a relevant role in pathogenesis.

An Atomic Resolution Model for Assembly, Architecture, and Function of the Dr Adhesins

Pathogenic bacteria possess adhesion protein complexes that play essential roles in targeting host cells and in propagating infection. Although each family of adhesion proteins is generally associated with a specific human disease, the Dr family from Escherichia coli is a notable exception, as its members are associated with both diarrheal and urinary tract infections. These proteins are reported to form both fimbrial and afimbrial structures at the bacterial cell surface and target a common host cell receptor, the decay-accelerating factor (DAF or CD55). Using the newly solved three-dimensional structure of AfaE, we have constructed a robust atomic resolution model that reveals the structural basis for assembly by donor strand complementation and for the architecture of capped surface fibers.

Interaction of Dr adhesin with collagen type IV is a critical step in Escherichia coli renal persistence

The pathogenic mechanism of recurrent or chronic urinary tract infection is poorly understood. Escherichia coli cells bearing Dr fimbriae display unique tropism to the basement membrane (BM)-renal interstitium that enables the bacteria to cause chronic pyelonephritis in experimental mice. The renal receptors for Dr-fimbriated E. coli are type IV collagen and decay-accelerating factor (DAF). We hypothesized that type IV collagen receptor-mediated BM-interstitial tropism is essential for E. coli to cause chronic pyelonephritis. To test the role of the type IV collagen tropism of Dr-fimbriated E. coli in renal persistence, we constructed an isogenic mutant in the DraE adhesin subunit that was unable to bind type IV collagen but retained binding to DAF and examined its virulence in the mouse model. The collagen-binding mutant DrI113T was eliminated from the mouse renal tissues in 6 to 8 weeks, while the parent strain caused persistent renal infection that lasted at least 14 weeks (P < or = 0.02). Transcomplementation with the intact Dr operon restored collagen-binding activity, BM-interstitial tropism, and the ability to cause persistent renal infection. We conclude that type IV collagen binding mediated by DraE adhesin is a critical step for the development of persistent renal infection in a murine model of E. coli pyelonephritis.

Identification of an extracellular matrix protein adhesin, EmaA, which mediates the adhesion of Actinobacillus actinomycetemcomitans to collagen

Actinobacillus actinomycetemcomitansis an aetiologic agent in the development of periodontal and some systemic diseases in humans. This pathogen localizes to the underlying connective tissue of the oral cavity in individuals with periodontal disease. The adhesion ofA. actinomycetemcomitansto extracellular matrix components of the connective tissue prompted this study to identify gene products mediating the interaction ofA. actinomycetemcomitansto these molecules. A transposon mutagenesis system was optimized for use inA. actinomycetemcomitansand used to generate an insertional mutant library. A total of 2300 individual insertion transposon mutants were screened for changes in the adhesion to collagen and fibronectin. Mutants were identified which exhibited the following phenotypes: a decrease in collagen binding; a decrease in fibronectin binding; a decrease in binding to both proteins; and an increase in binding to both collagen and fibronectin. The identification of mutants defective in adhesion to the individual proteins indicates that distinct adhesins are expressed by this organism. Molecular analysis of these mutants implicated 11 independent loci in protein adhesion. One gene,emaA, is likely to encode a direct mediator of collagen adhesion, based on predicted protein features homologous to the collagen-binding protein YadA ofYersinia enterocolitica. EmaA was localized to the outer membrane, as expected for an adhesin. Reduction in fibronectin adhesion appeared to be influenced by abrogation of proteins involved in molybdenum-cofactor biosynthesis. Several other loci identified as reducing or increasing adhesion to both collagen and fibronectin are suggested to be involved in regulatory cascades that promote or repress expression of collagen and fibronectin adhesins. Collectively, the results support the hypothesis thatA. actinomycetemcomitanshost colonization involves afimbrial adhesins for extracellular matrix proteins, and that the expression of adhesion is modulated by global regulatory mechanisms.

Human diffusely adhering Escherichia coli expressing Afa/Dr adhesins that use human CD55 (decay-accelerating factor) as a receptor does not bind the rodent and pig analogues of CD55

Afa/Dr diffusely adhering Escherichia coli (DAEC) bacteria that are responsible for recurrent urinary tract and gastrointestinal infections recognized as a receptor the glycosylphosphatidylinositol (GPI)-anchored protein decay-accelerating factor (DAF; CD55) at the brush border of cultured human intestinal cells. Results show that Afa/Dr DAEC C1845 bacteria were poorly associated with the mucosa of the gastrointestinal tract of infected mice. We conducted experiments with Chinese hamster ovary (CHO) cells stably transfected with mouse (GPI or transmembrane forms), pig, or human CD55 or mouse Crry cDNAs or transfected with empty vector pDR2EF1 alpha. Recombinant E. coli AAEC185 bacteria expressing Dr or F1845 adhesins bound strongly to CHO cells expressing human CD55 but not to the CHO cells expressing mouse (transmembrane and GPI anchored), rat, or pig CD55 or mouse Crry. Positive clustering of CD55 around Dr-positive bacteria was observed in human CD55-expressing CHO cells but not around the rarely adhering Dr-positive bacteria randomly distributed at the cell surface of CHO cells expressing mouse, rat, or pig CD55.

Chimeric Dr fimbriae with a herpes simplex virus type 1 epitope as a model for a recombinant vaccine

The potential of the major structural protein DraE of Escherichia coli Dr fimbriae has been used to display an 11-amino-acid peptide of glycoprotein D derived from herpes simplex virus (HSV) type 1. The heterologous sequence mimicking an epitope from glycoprotein D was inserted in one copy into the draE gene in place of a predicted 11-amino-acid sequence in the N-terminal region of surface-exposed domain 2 within the conserved disulfide loop (from Cys21 to Cys53). The inserted epitope was displayed on the surface of the chimeric DraE protein as evidenced by immunofluorescence and was recognized by monoclonal antibodies to the target HSV glycoprotein D antigen. Conversely, immunization of rabbits with purified chimeric Dr-HSV fimbriae resulted in a serum that specifically recognized the 11-amino-acid epitope of HSV glycoprotein D, indicating the utility of the strategy employed.