Escherichia coli DraE adhesin-associated bacterial internalization by epithelial cells is promoted independently by decay-accelerating factor and carcinoembryonic antigen-related cell adhesion molecule binding and does not require the DraD invasin

Uropathogenic Escherichia coli (UPEC)-Associated Urinary Tract Infections: The Molecular Basis for Challenges to Effective Treatment

Urinary tract infections (UTIs) are among the most common bacterial infections, especially among women and older adults, leading to a significant global healthcare cost burden. Uropathogenic Escherichia coli (UPEC) are the most common cause and accounts for the majority of community-acquired UTIs. Infection by UPEC can cause discomfort, polyuria, and fever. More serious clinical consequences can result in urosepsis, kidney damage, and death. UPEC is a highly adaptive pathogen which presents significant treatment challenges rooted in a complex interplay of molecular factors that allow UPEC to evade host defences, persist within the urinary tract, and resist antibiotic therapy. This review discusses these factors, which include the key genes responsible for adhesion, toxin production, and iron acquisition. Additionally, it addresses antibiotic resistance mechanisms, including chromosomal gene mutations, antibiotic deactivating enzymes, drug efflux, and the role of mobile genetic elements in their dissemination. Furthermore, we provide a forward-looking analysis of emerging alternative therapies, such as phage therapy, nano-formulations, and interventions based on nanomaterials, as well as vaccines and strategies for immunomodulation. This review underscores the continued need for research into the molecular basis of pathogenesis and antimicrobial resistance in the treatment of UPEC, as well as the need for clinically guided treatment of UTIs, particularly in light of the rapid spread of multidrug resistance.

Interactions of pathogenic Escherichia coli with CEACAMs

The pathogenic Escherichia coli can be parsed into specific variants (pathovars) depending on their phenotypic behavior and/or expression of specific virulence factors. These pathogens are built around chromosomally-encoded core attributes and through acquisition of specific virulence genes that direct their interaction with the host. Engagement of E. coli pathovars with CEACAMs is determined both by core elements common to all E. coli as well as extrachromosomally-encoded pathovar-specific virulence traits, which target amino terminal immunoglobulin variable-like (IgV) regions of CEACAMs. Emerging data suggests that engagement of CEACAMs does not unilaterally benefit the pathogen and that these interactions may also provide an avenue for pathogen elimination.

Virulence factors of uropathogens and their role in host pathogen interactions

Gram-positive and Gram-negative bacterial pathogens are commonly found in Urinary Tract Infection (UTI), particularly infected in females like pregnant women, elder people, sexually active, or individuals prone to other risk factors for UTI. In this article, we review the expression of virulence surface proteins and their interaction with host cells for the most frequently isolated uropathogens: Escherichia coli, Enterococcus faecalis, Proteus mirabilis, Klebsiella pneumoniae, and Staphylococcus saprophyticus. In addition to the host cell interaction, surface protein regulation was also discussed in this article. The surface protein regulation serves as a key tool in differentiating the pathogen isotypes. Furthermore, it might provide insights on novel diagnostic methods to detect uropathogen that are otherwise easily overlooked due to limited culture-based assays. In essence, this review shall provide an in-depth understanding on secretion of virulence factors of various uropathogens and their role in host-pathogen interaction, this knowledge might be useful in the development of therapeutics against uropathogens.

Animal Models and Pathogenesis of Ulcerative Colitis

Background

Ulcerative colitis (UC) is a kind of inflammatory bowel disease which is needed to be predicted.

Objective

To analyze various animal models of UC conditions and summarizes the animal selection, model progression, and pathogenic mechanisms of UC animal models.

Methods

We surveyed the research papers published in PubMed, Google Scholar, Baidu Scholar, CNKI, SciFinder, and Web of Science in the past 5 years and discussed the experimental animals, modeling methods, and pathogenic mechanisms.

Results

In the selection of experimental animals, rats are considered the best experimental animals. The mainstream modeling methods can be categorized into the chemical stimulation method, immune stimulation method, and compound method, among which the compound method is the most successful. In the study of the pathogenesis of UC, the pathogenesis of UC is due to various pathogenic factors, such as nitric oxide (NO), prostaglandins (PG), proinflammatory factors (IL, TNF-α), and intestinal flora.

Conclusion

The method of building an animal model of UC is well-established, providing a more targeted selection of animal models for future related experiments.

Immunoglobulin-fold containing bacterial adhesins: molecular and structural perspectives in host tissue colonization and infection

Immunoglobulin (Ig) domains are one of the most widespread protein domains encoded by the human genome and are present in a large array of proteins with diverse biological functions. These Ig domains possess a central structure, the immunoglobulin-fold, which is a sandwich of two β sheets, each made up of anti-parallel β strands, surrounding a central hydrophobic core. Apart from humans, proteins containing Ig-like domains are also distributed in a vast selection of organisms including vertebrates, invertebrates, plants, viruses and bacteria where they execute a wide array of discrete cellular functions. In this review, we have described the key structural deviations of bacterial Ig-folds when compared to the classical eukaryotic Ig-fold. Further, we have comprehensively grouped all the Ig-domain containing adhesins present in both Gram-negative and Gram-positive bacteria. Additionally, we describe the role of these particular adhesins in host tissue attachment, colonization and subsequent infection by both pathogenic and non-pathogenic Escherichia coli as well as other bacterial species. The structural properties of these Ig-domain containing adhesins, along with their interactions with specific Ig-like and non Ig-like binding partners present on the host cell surface have been discussed in detail.

Acinetobacter baumannii Targets Human Carcinoembryonic Antigen-Related Cell Adhesion Molecules (CEACAMs) for Invasion of Pneumocytes

Multidrug-resistant Acinetobacter baumannii is regarded as a life-threatening pathogen mainly associated with nosocomial and community-acquired pneumonia. Here, we show that A. baumannii can bind the human carcinoembryonic antigen-related cell adhesion molecule (CEACAM) receptors CEACAM1, CEACAM5, and CEACAM6. This specific interaction enhances A. baumannii internalization in membrane-bound vacuoles, promptly decorated with Rab5, Rab7, and lipidated microtubule-associated protein light chain 3 (LC3). Dissecting intracellular signaling pathways revealed that infected pneumocytes trigger interleukin-8 (IL-8) secretion via the extracellular signal-regulated kinase (ERK)1/2 and nuclear factor-kappa B (NF-κB) signaling pathways for A. baumannii clearance. However, in CEACAM1-L-expressing cells, IL-8 secretion lasts only 24 h, possibly due to an A. baumannii-dependent effect on the CEACAM1-L intracellular domain. Conversely, the glycosylphosphatidylinositol-anchored CEACAM5 and CEACAM6 activate the c-Jun NH₂-terminal kinase (JNK)1/2-Rubicon-NOX2 pathway, suggestive of LC3-associated phagocytosis. Overall, our data show for the first time novel mechanisms of adhesion to and invasion of pneumocytes by A. baumannii via CEACAM-dependent signaling pathways that eventually lead to bacterial killing. These findings suggest that CEACAM upregulation could put patients at increased risk of lower respiratory tract infection by A. baumannii IMPORTANCE This work shows for the first time that Acinetobacter baumannii binds to carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM1), CEACAM5, and CEACAM6. This binding significantly enhances A. baumannii internalization within alveolar host cell epithelia. Intracellular trafficking involves typical Rab5 and Rab7 vacuolar proteins as well as light chain 3 (LC3) and slowly progresses to bacterial killing by endosome acidification. CEACAM engagement by A. baumannii leads to distinct and specific downstream signaling pathways. The CEACAM1 pathway finely tunes interleukin-8 (IL-8) secretion, whereas CEACAM5 and CEACAM6 mediate LC3-associated phagocytosis. The present study provides new insights into A. baumannii-host interactions and could represent a promising therapeutic strategy to reduce pulmonary infections caused by this pathogen.

Genomic Surveillance of Ceftriaxone-Resistant Escherichia coli in Western New York Suggests the Extended-Spectrum β-Lactamase bla CTX-M-27 Is Emerging on Distinct Plasmids in ST38

Extended-spectrum β-lactamase (ESBL)-producing Enterobacteriaceae pose significant treatment and infection prevention challenges. Escherichia coli sequence type (ST) 131 associated with the bla_CTX-M-15 gene has been the dominant lineage of ESBL-producing E. coli in the US and worldwide. In this study, our objective was to determine the β-lactamase profile, means of dissemination, prevalence, and the clonal identity of ESBL-producing E. coli in our region of Western New York. Whole-genome SNP-based phylogenomics was used to assess 89 ceftriaxone-resistant (CTR) E. coli. Isolates were collected from both inpatients and outpatients and from urine and sterile-sites over a 2 month period in 2017 or throughout the year, respectively. ST131 was the predominant ST (46.0%), followed by ST38 (15.7%). The bla_CTX-M-15 gene was commonly found in 53.7% of ST131 isolates, whereas the bla_CTX-M-27 gene was found in 26.8% of ST131, though was significantly associated with ST38, and was found in 71.4% of those strains. When compared to ST131, ST38 E. coli exhibited increased frequency of resistance to nitrofurantoin and decreased frequency of resistance to ciprofloxacin and ampicillin-sulbactam. Using Nanopore long-read sequencing technology, an analysis of the ESBL genetic context showed that the bla_CTX-M-15 gene was chromosomal in 68.2% of ST131, whereas the bla_CTX-M-27 gene was plasmid-borne in all ST131 and 90% of ST38 isolates. Notably, the bla_CTX-M-27 gene in ST38 resided on highly-related (99.0–100.0% identity and 65.0–98.0% query coverage) conjugative IncF plasmids of distinct plasmid multi-locus sequence types (pMLSTs) from those in ST131. Furthermore, ST131 and ST38 were found to harbor different antibiotic resistance gene and virulence factor profiles. These findings raise the possibility of an emerging ESBL-producing E. coli lineage in our region.

Biomarkers that differentiate false positive urinalyses from true urinary tract infection

BACKGROUND

The specificity of the leukocyte esterase test (87%) is suboptimal. The objective of this study was to identify more specific screening tests that could reduce the number of children who unnecessarily receive antimicrobials to treat a presumed urinary tract infection (UTI).

METHODS

Prospective cross-sectional study to compare inflammatory proteins in blood and urine samples collected at the time of a presumptive diagnosis of UTI. We also evaluated serum RNA expression in a subset.

RESULTS

We enrolled 200 children; of these, 89 were later demonstrated not to have a UTI based on the results of the urine culture obtained. Urinary proteins that best discriminated between children with UTI and no UTI were involved in T cell response proliferation (IL-9, IL-2), chemoattractants (CXCL12, CXCL1, CXCL8), the cytokine/interferon pathway (IL-13, IL-2, INFγ), or involved in innate immunity (NGAL). The predictive power (as measured by the area under the curve) of a combination of four urinary markers (IL-2, IL-9, IL-8, and NGAL) was 0.94. Genes in the pathways related to inflammation were also upregulated in serum of children with UTI.

CONCLUSIONS

Urinary proteins involved in the inflammatory response may be useful in identifying children with false positive results with current screening tests for UTI; this may reduce unnecessary treatment.

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.

Carcinoembryonic antigen (CEACAM) family members and Inflammatory Bowel Disease

Inflammatory bowel disease (IBD), encompassing Crohn's disease (CD) and ulcerative colitis (UC), is a chronic intestinal inflammatory condition with increasing incidence worldwide and whose pathogenesis remains largely unknown. The collected evidence indicates that genetic, environmental and microbial factors and a dysregulated immune response are responsible for the disease. IBD has an early onset and long term sufferers present a higher risk of developing colitis associated cancer (CAC). The carcinoembryonic antigen-related adhesion molecules (CEACAM) are a subgroup of the CEA family, found in a range of different cell types and organs including epithelial cells in the intestine. They can act as intercellular adhesions molecules for e.g. bacteria and soluble antigens. CEACAMs are involved in a number of different processes including cell adhesion, proliferation, differentiation and tumour suppression. Some CEACAMs such as CEACAM1, CEACAM5 and CEACAM6 are highly associated with cancer and are even recognised as valid clinical markers for certain cancer forms. However, their role in IBD pathogenesis is less understood. The purpose of this review is to provide a comprehensive summary of published literature on CEACAMs and intestinal inflammation (IBD). The interactions between CEACAMs and bacteria adhesion in relation to IBD pathophysiology will be addressed and potential new therapeutic and diagnostic opportunities will be identified.

Inhibition of CEA release from epithelial cells by lipid A of Gram-negative bacteria

A number of bacterial species, both pathogenic and non-pathogenic, use the human CEACAM family members as receptors for internalization into epithelial cells. The GPI-linked CEA and CEACAM6 might play a role in the innate immune defense, protecting the colon from microbial invasion. Previous studies showed that CEA is released from epithelial cells by an endogenous GPI-PLD enzyme. GPI-PLD activity was reported to be inhibited by several synthetic and natural forms of lipid A. We hypothesized that CEA engagement by Gram-negative bacteria might attenuate CEA release from epithelial cells and that this might facilitate bacterial colonization. We tested the hypothesis by examining the effect of Escherichia coli on CEA release from colorectal cancer cells in a co-culture experiment. A subconfluent monolayer culture of colorectal cancer cells (LS-180, Caco-2 and HT29/219) was incubated with E. coli. While there was a significant reduction in CEA secretion from LS-180 and HT29/219 cells, we found only a small reduction of CEA shedding from Caco-2 cells compared to the level from the untreated control cells. Furthermore, lipid A treatment of LS-180 cells inhibited CEA release from the cells in a dosedependent manner. Western blot analysis of total lysates showed that CEA expression levels in cells co-cultured with bacteria did not differ from those in untreated control cells. These results suggest that lipid A of Gram-negative bacteria might play a role in preventing the release of CEA from mucosal surfaces and promote mucosal colonization by bacteria.

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.

Virulence factors of uropathogenic E. coli and their interaction with the host

Urinary tract infections (UTIs) belong to the most common infectious diseases worldwide. The most frequently isolated pathogen from uncomplicated UTIs is Escherichia coli. To establish infection in the urinary tract, E. coli has to overcome several defence strategies of the host, including the urine flow, exfoliation of urothelial cells, endogenous antimicrobial factors and invading neutrophils. Thus, uropathogenic E. coli (UPEC) harbour a number of virulence and fitness factors enabling the bacterium to resist and overcome these different defence mechanisms. There is no particular factor which allows the identification of UPEC among the commensal faecal flora apart from the ability to enter the urinary tract and cause an infection. Many of potential virulence or fitness factors occur moreover with high redundancy. Fimbriae are inevitable for adherence to and invasion into the host cells; the type 1 pilus is an established virulence factor in UPEC and indispensable for successful infection of the urinary tract. Flagella and toxins promote bacterial dissemination, while different iron-acquisition systems allow bacterial survival in the iron-limited environment of the urinary tract. The immune response to UPEC is primarily mediated by toll-like receptors recognising lipopolysaccharide, flagella and other structures on the bacterial surface. UPEC have the capacity to subvert this immune response of the host by means of actively impacting on pro-inflammatory signalling pathways, or by physical masking of immunogenic structures. The large repertoire of bacterial virulence and fitness factors in combination with host-related differences results in a complex interaction between host and pathogen in the urinary tract.

Structural insight into host recognition by aggregative adherence fimbriae of enteroaggregative Escherichia coli

Enteroaggregative Escherichia coli (EAEC) is a leading cause of acute and persistent diarrhea worldwide. A recently emerged Shiga-toxin-producing strain of EAEC resulted in significant mortality and morbidity due to progressive development of hemolytic-uremic syndrome. The attachment of EAEC to the human intestinal mucosa is mediated by aggregative adherence fimbria (AAF). Using X-ray crystallography and NMR structures, we present new atomic resolution insight into the structure of AAF variant I from the strain that caused the deadly outbreak in Germany in 2011, and AAF variant II from archetype strain 042, and propose a mechanism for AAF-mediated adhesion and biofilm formation. Our work shows that major subunits of AAF assemble into linear polymers by donor strand complementation where a single minor subunit is inserted at the tip of the polymer by accepting the donor strand from the terminal major subunit. Whereas the minor subunits of AAF have a distinct conserved structure, AAF major subunits display large structural differences, affecting the overall pilus architecture. These structures suggest a mechanism for AAF-mediated adhesion and biofilm formation. Binding experiments using wild type and mutant subunits (NMR and SPR) and bacteria (ELISA) revealed that despite the structural differences AAF recognize a common receptor, fibronectin, by employing clusters of basic residues at the junction between subunits in the pilus. We show that AAF-fibronectin attachment is based primarily on electrostatic interactions, a mechanism not reported previously for bacterial adhesion to biotic surfaces.

Enteroaggregative Escherichia coli (EAEC) is a major cause of diarrhea worldwide and is commonly present as an infection in symptomatic travelers returning from developing countries. The attachment of EAEC to the human intestine is mediated protein filaments extending from the bacterial surface known as aggregative adherence fimbria (AAF). Here we use X-ray crystallography and nuclear magnetic resonance (NMR) structures to provide an atomic structure of the protein fibers made by the two major variants, AAF/I and AAF/II. The structures of the major subunit proteins show that the AAFs assemble into flexible, linear polymers that are capped by a single minor protein subunit at the tip. Biochemical assays reveal that the AAFs recognize a common receptor, the extracellular matrix protein fibronectin, via clusters of positively-charged amino acid residues running along the length of the fimbriae. Our structures suggest a unique mechanism based on ionic interactions for AAF-mediated receptor binding and biofilm formation.

Colonic mucosa-associated diffusely adherent afaC+ Escherichia coli expressing lpfA and pks are increased in inflammatory bowel disease and colon cancer

OBJECTIVE

Colonic mucosa-associated Escherichia coli are increased in Crohn's disease (CD) and colorectal cancer (CRC). They variously haemagglutinate, invade epithelial cell lines, replicate within macrophages, translocate across M (microfold) cells and damage DNA. We investigated genes responsible for these effects and their co-association in colonic mucosal isolates.

DESIGN

A fosmid library yielding 968 clones was prepared in E coli EPI300-T1 using DNA from a haemagglutinating CRC isolate, and resulting haemagglutinating clones were 454-pyrosequenced. PCR screening was performed on 281 colonic E coli isolates from inflammatory bowel disease (IBD) (35 patients), CRC (21) and controls (24; sporadic polyps or irritable bowel syndrome).

RESULTS

454-Pyrosequencing of fosmids from the haemagglutinating clones (n=8) identified the afimbrial adhesin afa-1 operon. Transfection of afa-1 into E coli K-12 predictably conferred diffuse adherence plus invasion of HEp-2 and I-407 epithelial cells, and upregulation of vascular endothelial growth factor. E coli expressing afaC were common in CRC (14/21, p=0.0009) and CD (9/14, p=0.005) but not ulcerative colitis (UC; 8/21) compared with controls (4/24). E coli expressing both afaC and lpfA (relevant to M-cell translocation) were common in CD (8/14, p=0.0019) and CRC (14/21, p=0.0001), but not UC (6/21) compared with controls (2/24). E coli expressing both afaC and pks (genotoxic) were common in CRC (11/21, p=0.0015) and UC (8/21, p=0.022), but not CD (4/14) compared with controls (2/24). All isolates expressed dsbA and htrA relevant to intra-macrophage replication, and 242/281 expressed fimH encoding type-1 fimbrial adhesin.

CONCLUSIONS

IBD and CRC commonly have colonic mucosal E coli that express genes that confer properties relevant to pathogenesis including M-cell translocation, angiogenesis and genotoxicity.

Signaling by epithelial members of the CEACAM family - mucosal docking sites for pathogenic bacteria

Carcinoembryonic antigen-related cell adhesion molecules (CEACAMs) comprise a group of immunoglobulin-related vertebrate glycoproteins. Several family members, including CEACAM1, CEA, and CEACAM6, are found on epithelial tissues throughout the human body. As they modulate diverse cellular functions, their signaling capacity is in the focus of current research. In this review we will summarize the knowledge about common signaling processes initiated by epithelial CEACAMs and suggest a model of signal transduction by CEACAM family members lacking significant cytoplasmic domains. As pathogenic and non-pathogenic bacteria exploit these receptors during mucosal colonization, we try to highlight the connection between CEACAMs, microbes, and cellular responses. Special emphasis in this context is placed on the functional interplay between CEACAMs and integrins that influences matrix adhesion of epithelial cells. The cooperation between these two receptor families provides an intriguing example of the fine tuning of cellular responses and their manipulation by specialized microorganisms.

Pathogenesis of human enterovirulent bacteria: lessons from cultured, fully differentiated human colon cancer cell lines

Hosts are protected from attack by potentially harmful enteric microorganisms, viruses, and parasites by the polarized fully differentiated epithelial cells that make up the epithelium, providing a physical and functional barrier. Enterovirulent bacteria interact with the epithelial polarized cells lining the intestinal barrier, and some invade the cells. A better understanding of the cross talk between enterovirulent bacteria and the polarized intestinal cells has resulted in the identification of essential enterovirulent bacterial structures and virulence gene products playing pivotal roles in pathogenesis. Cultured animal cell lines and cultured human nonintestinal, undifferentiated epithelial cells have been extensively used for understanding the mechanisms by which some human enterovirulent bacteria induce intestinal disorders. Human colon carcinoma cell lines which are able to express in culture the functional and structural characteristics of mature enterocytes and goblet cells have been established, mimicking structurally and functionally an intestinal epithelial barrier. Moreover, Caco-2-derived M-like cells have been established, mimicking the bacterial capture property of M cells of Peyer's patches. This review intends to analyze the cellular and molecular mechanisms of pathogenesis of human enterovirulent bacteria observed in infected cultured human colon carcinoma enterocyte-like HT-29 subpopulations, enterocyte-like Caco-2 and clone cells, the colonic T84 cell line, HT-29 mucus-secreting cell subpopulations, and Caco-2-derived M-like cells, including cell association, cell entry, intracellular lifestyle, structural lesions at the brush border, functional lesions in enterocytes and goblet cells, functional and structural lesions at the junctional domain, and host cellular defense responses.

Pathogens use structural mimicry of native host ligands as a mechanism for host receptor engagement

A pathogen's ability to engage host receptors is a critical determinant of its host range and interspecies transmissibility, key issues for understanding emerging diseases. However, the identification of host receptors, which are also attractive drug targets, remains a major challenge. Our structural bioinformatics studies reveal that both bacterial and viral pathogens have evolved to structurally mimic native host ligands (ligand mimicry), thus enabling engagement of their cognate host receptors. In contrast to the structural homology, amino acid sequence similarity between pathogen molecules and the mimicked host ligands was low. We illustrate the utility of this concept to identify pathogen receptors by delineating receptor tyrosine kinase Axl as a candidate receptor for the polyomavirus SV40. The SV40-Axl interaction was validated, and its participation in the infection process was verified. Our results suggest that ligand mimicry is widespread, and we present a quick tool to screen for pathogen-host receptor interactions.

Comparison of adhesin genes and antimicrobial susceptibilities between uropathogenic and intestinal commensal Escherichia coli strains

The presence of adhesins is arguably an important determinant of pathogenicity for Uropathogenic Escherichia coli (UPEC). Antimicrobial susceptibilities were tested by agar dilution method, fifteen adhesin genes were detected by polymerase chain reaction, and multilocus sequence typing (MLST) was analyzed in 70 UPEC isolates and 41 commensal E. coli strains. Extended-spectrum β-lactamase (ESBL) was determined with confirmatory test. The prevalence of ESBL-producers in UPEC (53%, 37/70) was higher than the commensal intestinal isolates (7%, 3/41), and 97% (36/37) of the ESBL-producing UPEC harbored bla_CTX-M genes. afa was present in 36% (10/28) UPEC isolates from recurrent lower urinary tract infection (UTI), and none in the acute pyelonephritis, acute uncomplicated cystitis or commensal strains (P<0.0001). papG was detected in 28% (20/70) of UPEC isolates, while 5% (2/41) of the commensal strains were papG positive (P = 0.0025), and the prevalence of papG was significantly higher in acute pyelonephritis group (71%) than the other two UTI groups (P<0.0001). The prevalence of flu, yqi, yadN and ygiL was significantly higher in UPEC isolates than in the commensal strains. ESBL-producing UPEC showed a lower prevalence of adhesin genes compared with non-ESBL-producing strains. The MLST profiles were different between UPEC and commensal strains, with ST131 (19%, 13/70) and ST10 (20%, 8/41) being the most common MLSTs, respectively. This study demonstrated that several adhesin genes were more prevalent in UPEC isolates than in commensal E. coli, and afa may be associated with recurrent lower UTI whereas papG is more frequently associated with acute pyelonephritis.

Moraxella catarrhalis: from interactions with the host immune system to vaccine development

Moraxella catarrhalis is a human-restricted commensal that over the last two decades has developed into an emerging respiratory tract pathogen. The bacterial species is equipped with various adhesins to facilitate its colonization. Successful evasion of the human immune system is a prerequisite for Moraxella infection. This strategy involves induction of an excessive proinflammatory response, intervention of granulocyte recruitment to the infection site, activation of selected pattern recognition receptors and cellular adhesion molecules to counteract the host bacteriolytic attack, as well as, finally, reprogramming of antigen presenting cells. Host immunomodulator molecules are also exploited by Moraxella to aid in resistance against complement killing and host bactericidal molecules. Thus, breaking the basis of Moraxella immune evasion mechanisms is fundamental for future invention of effective therapy in controlling Moraxella infection.

Morphological Changes of Bladder Mucosa in Patients Who Underwent Instillation with Combined Sodium Hyaluronic Acid-Chondroitin Sulphate (Ialuril®)

<b><i>Objective:</i></b> To investigate what changes are endoscopically evident after glycosaminoglycans (GAGs) therapy by hyaluronic acid (HA) and chondroitin sulphate (CS) (Ialuril®) in female patients affected by bladder pain syndrome(BPS)/ interstitial cystitis (IC) or recurrent urinary tract infections (rUTIs). <b><i>Patients and Methods:</i></b> 21 female patients over 18 years affected by rUTIs or BPS/IC received intravesical instillation of HA and CS (4 weekly instillations followed by 2 instillations every 2 weeks and 2 instillation monthly). Post-treatment evaluation included cystoscopy and patient assessment of improvement in symptoms and satisfaction on a visual analogue scale (VAS) from 0 to 10. <b><i>Results:</i></b> The post-treatment endoscopy showed a positive effect on bladder mucosa morphology. In 2 cases, treatment did not change endoscopic findings and clinical symptoms. In the other patients, when macroscopic features of the bladder mucosa normalized, the clinical picture improved. <b><i>Conclusions:</i></b> GAGs therapy by HA and CS (Ialuril) improves the morphology of bladder mucosa in patients with rUTI or BPS/IC.

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.

Role of Src kinases in mobilization of glycosylphosphatidylinositol-anchored decay-accelerating factor by Dr fimbria-positive adhering bacteria

Afa/Dr fimbriae constitute the major virulence factor of diffusely adhering Escherichia coli (Afa/Dr DAEC). After recognizing membrane-bound signaling receptors, they trigger cell responses. One of these receptors is the human decay-accelerating factor (hDAF). It has previously been reported that the binding of Afa/Dr fimbriae to hDAF quickly induces recruitment of hDAF around adhering bacteria. The aim of our study is to analyze the role of Src kinases in the Dr fimbria-induced recruitment of hDAF. Using biochemical methods and confocal microscopy followed by 3-dimensional (3D) analysis, we have shown that the activation and cell membrane targeting of Src kinases are necessary for the recruitment and organization of hDAF around adhering bacteria. We identified c-Src to be the specific kinase involved in this process. Using a set of Src-green fluorescent protein mutants, we showed that the catalytic activity and the Src homology 2 (SH2) and SH3 domains of the Src kinases are necessary for Dr fimbria-induced hDAF mobilization to occur. In addition, using mutated Dr fimbriae and a set of mutated hDAFs in which each of the complement control protein (CCP) domains had successively been deleted, we found that the aspartic acids at position 54 in the Dr fimbriae and in CCP domain 4 of hDAF played pivotal roles in the mobilization of the Src kinases and hDAF, respectively.

Grading the commercial optical biosensor literature-Class of 2008: 'The Mighty Binders'

Optical biosensor technology continues to be the method of choice for label-free, real-time interaction analysis. But when it comes to improving the quality of the biosensor literature, education should be fundamental. Of the 1413 articles published in 2008, less than 30% would pass the requirements for high-school chemistry. To teach by example, we spotlight 10 papers that illustrate how to implement the technology properly. Then we grade every paper published in 2008 on a scale from A to F and outline what features make a biosensor article fabulous, middling or abysmal. To help improve the quality of published data, we focus on a few experimental, analysis and presentation mistakes that are alarmingly common. With the literature as a guide, we want to ensure that no user is left behind.

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.

Bacterial adhesins in host-microbe interactions

Most commensal and pathogenic bacteria interacting with eukaryotic hosts express adhesive molecules on their surfaces that promote interaction with host cell receptors or with soluble macromolecules. Even though bacterial attachment to epithelial cells may be beneficial for bacterial colonization, adhesion may come at a cost because bacterial attachment to immune cells can facilitate phagocytosis and clearing. Many pathogenic bacteria have solved this dilemma by producing an antiphagocytic surface layer usually consisting of polysaccharide and by expressing their adhesins on polymeric structures that extend out from the cell surface. In this review, we will focus on the interaction between bacterial adhesins and the host, with an emphasis on pilus-like structures.

Human decay-accelerating factor and CEACAM receptor-mediated internalization and intracellular lifestyle of Afa/Dr diffusely adhering Escherichia coli in epithelial cells

We used transfected epithelial CHO-B2 cells as a model to identify the mechanism mediating internalization of Afa/Dr diffusely adhering Escherichia coli. We provide evidence that neither the alpha5 or beta1 integrin subunits nor alpha5beta1 integrin functioned as a receptor mediating the adhesion and/or internalization of Dr or Afa-III fimbria-positive bacteria. We also demonstrated that (i) whether or not the AfaD or DraD invasin subunits were present, there was no difference in the cell association and entry of bacteria and that (ii) DraE or AfaE-III adhesin subunits are necessary and sufficient to promote the receptor-mediated bacterial internalization into epithelial cells expressing human decay-accelerating factor (DAF), CEACAM1, CEA, or CEACAM6. Internalization of Dr fimbria-positive E. coli within CHO-DAF, CHO-CEACAM1, CHO-CEA, or CHO-CEACAM6 cells occurs through a microfilament-independent, microtubule-dependent, and lipid raft-dependent mechanism. Wild-type Dr fimbria-positive bacteria survived better within cells expressing DAF than bacteria internalized within CHO-CEACAM1, CHO-CEA, or CHO-CEACAM6 cells. In DAF-positive cells, internalized Dr fimbria-positive bacteria were located in vacuoles that contained more than one bacterium, displaying some of the features of late endosomes, including the presence of Lamp-1 and Lamp-2, and some of the features of CD63 proteins, but not of cathepsin D, and were acidic. No interaction between Dr fimbria-positive-bacterium-containing vacuoles and the autophagic pathway was observed.