Synergy between Group 2 capsules and lipopolysaccharide underpins serum resistance in extra-intestinal pathogenic Escherichia coli.

Escherichia coli (E. coli) is a major cause of urinary tract infections, bacteraemia, and sepsis. CFT073 is a prototypic, urosepsis isolate of sequence type (ST) 73. This laboratory, among others, has shown that strain CFT073 is resistant to serum, with capsule and other extracellular polysaccharides imparting resistance. The interplay of such polysaccharides remains under-explored. This study has shown that CFT073 mutants deficient in lipopolysaccharide (LPS) O-antigen and capsule display exquisite serum sensitivity. Additionally, O-antigen and LPS outer core mutants displayed significantly decreased surface K2 capsule, coupled with increased unbound K2 capsule being detected in the supernatant. The R1 core and O6 antigen are involved in the tethering of K2 capsule to the CFT073 cell surface, highlighting the importance of the R1 core in serum resistance. The dependence of capsule on LPS was shown to be post-transcriptional and related to changes in cell surface hydrophobicity. Furthermore, immunofluorescence microscopy suggested that the surface pattern of capsule is altered in such LPS core mutants, which display a punctate capsule pattern. Finally, targeting LPS biosynthesis using sub-inhibitory concentrations of a WaaG inhibitor resulted in increased serum sensitivity and decreased capsule in CFT073. Interestingly, the dependency of capsule on LPS has been observed previously in other Enterobacteria, indicating that the synergy between these polysaccharides is not just strain, serotype or species-specific but may be conserved across several pathogenic Gram-negative species. Therefore, using WaaG inhibitor derivatives to target LPS is a promising therapeutic strategy to reduce morbidity and mortality by reducing or eliminating surface capsule.

Inhibition of Vascular Endothelial Cell Leak Following Escherichia coli Attachment in an Experimental Model of Sepsis.

OBJECTIVES: The vascular endothelium is a major target of sepsis-induced events, and endothelial activation accounts for much of the pathology of sepsis. Urinary tract infections and pneumonia caused by Escherichia coli are among of the most common infections causing sepsis in both community and hospital settings. Currently, there are no approved drugs on the market to treat the underlying pathophysiology of sepsis. The aim of this study is to elucidate the molecular mechanism by which E. coli induces endothelial injury as a result of attachment. DESIGN: Laboratory research using a hemodynamic perfusion ex vivo model. SETTING: Research Laboratories of Royal College of Surgeons in Ireland and Beaumont Hospital. PATIENTS: Ex vivo human vascular endothelial cells. INTERVENTIONS: Addition of αVß3 antagonist, cilengitide. MEASUREMENTS AND MAIN RESULTS: Clinical strains of E. coli isolated from patients with sepsis bound to sheared human endothelial cells under static and hemodynamic shear conditions. Binding was dependent on E. coli cell membrane protein outer membrane protein A attaching directly to endothelial cell integrin αVß3. Attachment resulted in disturbances in endothelial barrier integrity, as determined by loss of tight junction protein staining, permeability changes, and ultimately cell death by apoptosis. Using a low concentration of the αVß3 antagonist cilengitide or using a strain deficient in outer membrane protein A resulted in a significant reduction in endothelial dysfunction following infection. CONCLUSIONS: Inhibition of E. coli binding to endothelial cell αVß3 by cilengitide prevents endothelial dysfunction and may, therefore, present as a novel early therapeutic for the treatment of sepsis.

Isolation and identification of cell-specific microRNAs targeting a messenger RNA using a biotinylated anti-sense oligonucleotide capture affinity technique.

MicroRNAs (miRNAs) are small non-coding RNAs that regulate expression by translational repression or messenger RNA (mRNA) degradation. Although numerous bioinformatic prediction models exist to identify miRNA-mRNA interactions, experimental validation of bona fide interactions can be difficult and laborious. Few methods can comprehensively identify miRNAs that target a single mRNA. We have developed an experimental approach to search for miRNAs targeting any mRNA using a capture affinity assay involving a biotinylated DNA anti-sense oligonucleotide. This method identifies miRNAs targeting the full length of the mRNA. The method was tested using three separate mRNA targets: alpha-1 antitrypsin (AAT) mRNA, interleukin-8 mRNA and secretory leucoprotease inhibitor mRNA. AAT mRNA-specific and total miRNAs from three different cell lines (monocytic THP-1, bronchial epithelial 16HBE14o- and liver HepG2 cells) were profiled, and validation studies revealed that AAT mRNA-specific miRNAs functionally target the AAT mRNA in a cell-specific manner, providing the first evidence of innate miRNAs selectively targeting and modulating AAT mRNA expression. Interleukin-8 and secretory leucoprotease inhibitor mRNAs and their cognate miRNAs were also successfully captured using this approach. This is a simple and an efficient method to potentially identify miRNAs targeting sequences within the full length of a given mRNA transcript.

Long Non-Coding RNA Expression in Alpha-1 Antitrypsin Deficient Monocytes Pre- and Post-AAT Augmentation Therapy.

Long non-coding RNAs (lncRNAs) regulate gene expression. Their expression in alpha-1 antitrypsin (AAT) deficiency has not been investigated. Treatment of AAT deficiency involves infusion of plasma-purified AAT and this augmentation therapy has previously been shown to alter microRNA expression in monocytes of AAT-deficient (ZZ) individuals. Here, we assess the effect of AAT augmentation therapy on the lncRNA expression profile in ZZ monocytes. Peripheral blood monocytes were isolated from ZZ individuals pre (Day 0)- and post (Day 2)-AAT augmentation therapy. Arraystar lncRNA microarray profiling was performed; a total of 17,761 lncRNAs were detectable across all samples. The array identified 7509 lncRNAs with differential expression post-augmentation therapy, 3084 were increased and 4425 were decreased (fold change ≥ 2). Expression of many of these lncRNAs were similarly altered in ZZ monocytes treated ex vivo with 27.5 µM AAT for 4 h. These properties may contribute to the manifold effects of AAT augmentation therapy.

IL-8 dictates glycosaminoglycan binding and stability of IL-18 in cystic fibrosis.

Dysregulation of airway inflammation contributes to lung disease in cystic fibrosis (CF). Inflammation is mediated by inflammatory cytokines, including IL-8, which illustrates an increase in biological half-life and proinflammatory activity when bound to glycosaminoglycans (GAGs). The aim of this project was to compare IL-8 and IL-18 for their relative stability, activity, and interaction with GAGs, including chondroitin sulfate, hyaluronic acid, and heparan sulfate, present in high quantities in the lungs of patients with CF. Bronchoalveolar lavage fluid was collected from patients with CF (n = 28), non-CF controls (n = 14), and patients with chronic obstructive pulmonary disease (n = 12). Increased levels of IL-8 and reduced concentrations of IL-18 were detected in bronchial samples obtained from CF individuals. The low level of IL-18 was not a defect in IL-18 production, as the pro- and mature forms of the molecule were expressed and produced by CF epithelial cells and monocytes. There was, however, a marked competition between IL-8 and IL-18 for binding to GAGs. A pronounced loss of IL-18 binding capacity occurred in the presence of IL-8, which displaced IL-18 from these anionic-matrices, rendering the cytokine susceptible to proteolytic degradation by neutrophil elastase. As a biological consequence of IL-18 degradation, reduced levels of IL-2 were secreted by Jurkat T lymphocytes. In conclusion, a novel mechanism has been identified highlighting the potential of IL-8 to determine the fate of other inflammatory molecules, such as IL-18, within the inflammatory milieu of the CF lung.

A commensal gone bad: complete genome sequence of the prototypical enterotoxigenic Escherichia coli strain H10407.

In most cases, Escherichia coli exists as a harmless commensal organism, but it may on occasion cause intestinal and/or extraintestinal disease. Enterotoxigenic E. coli (ETEC) is the predominant cause of E. coli-mediated diarrhea in the developing world and is responsible for a significant portion of pediatric deaths. In this study, we determined the complete genomic sequence of E. coli H10407, a prototypical strain of enterotoxigenic E. coli, which reproducibly elicits diarrhea in human volunteer studies. We performed genomic and phylogenetic comparisons with other E. coli strains, revealing that the chromosome is closely related to that of the nonpathogenic commensal strain E. coli HS and to those of the laboratory strains E. coli K-12 and C. Furthermore, these analyses demonstrated that there were no chromosomally encoded factors unique to any sequenced ETEC strains. Comparison of the E. coli H10407 plasmids with those from several ETEC strains revealed that the plasmids had a mosaic structure but that several loci were conserved among ETEC strains. This study provides a genetic context for the vast amount of experimental and epidemiological data that have been published.

Mutagenesis of the Rns regulator of enterotoxigenic Escherichia coli reveals roles for a linker sequence and two helix-turn-helix motifs.

The pathogenesis of diarrhoeal disease due to human enterotoxigenic Escherichia coli absolutely requires the expression of fimbriae. The expression of CS1 fimbriae is positively regulated by the AraC-like protein Rns. AraC-like proteins are DNA-binding proteins that typically contain two helix-turn-helix (HTH) motifs. A program of pentapeptide insertion mutagenesis of the Rns protein was performed, and this revealed that both HTH motifs are required by Rns to positively regulate CS1 fimbrial gene expression. Intriguingly, a pentapeptide insertion after amino acid C102 reduced the ability of Rns to transactivate CS1 fimbrial expression. The structure of Rns in this vicinity (NACRS) was predicted to be disordered and thus might act as a flexible linker. This hypothesis was confirmed by deletion of this amino acid sequence from the Rns protein; a truncated protein that lacked this sequence was no longer functional. Strikingly, this sequence could be functionally substituted in vivo and in vitro by a flexible seven amino acid sequence from another E. coli AraC-like protein RhaS. Our data indicate that HTH motifs and a flexible sequence are required by Rns for maximal activation of fimbrial gene expression.

The Estrogen-Induced miR-19 Downregulates Secretory Leucoprotease Inhibitor Expression in Monocytes.

Compared to females, males are more susceptible to acute viral and other respiratory tract infections that display greater severity and higher mortality. In contrast, females tend to fare worse with chronic inflammatory diseases. Circulating 17ß-estradiol (E2) is a female-specific factor that may influence the progression of human lung diseases. Here we hypothesize that E2 modulates the inflammatory response of monocytes through microRNA (miRNA)-based modulation of secretory leucoprotease inhibitor (SLPI), an antiprotease with immunomodulatory effects. Monocytic cells were treated ± E2, and differentially expressed miRNAs were identified using PCR profiling. Cells were transfected with miRNA mimics or antimiRs and SLPI mRNA and protein levels were quantified. Luciferase activity assay using wildtype and ΔmiR-19a/b-SLPI3'UTR reporter constructs and chromatin immunoprecipitation on E2-treated monocytes were performed. E2 downregulated SLPI and upregulated miR-19 expression in monocytes. Transfection with premiR-19b reduced SLPI mRNA and protein levels and this effect was abrogated using antimiRs against miR-19b. miR-19b directly binds the SLPI 3'UTR. The mechanism responsible for E2-mediated upregulation of miR-19 occurs via increased MIR17HG promoter activity mediated by c-MYC. Overall E2 decreases SLPI expression in human monocytic cells, via changes in miRNA expression and highlights the potential for estrogen to modulate the innate immune system.

The hek outer membrane protein of Escherichia coli strain RS218 binds to proteoglycan and utilizes a single extracellular loop for adherence, invasion, and autoaggregation.

Escherichia coli is the principal gram-negative causative agent of sepsis and meningitis in neonates. The pathogenesis of meningitis due to E. coli K1 involves mucosal colonization, transcytosis of epithelial cells, survival in the bloodstream, and eventually invasion of the meninges. The last two aspects have been well characterized at a molecular level. Less is known about the early stages of pathogenesis, i.e., adhesion to and invasion of epithelial cells. We have previously reported that the Hek protein causes autoaggregation and can mediate adherence to and invasion of epithelial cells. Here, we report that Hek-mediated adherence is dependent on binding to glycosoaminoglycan, in particular, heparin. The ability to hemagglutinate, autoaggregate, adhere, and invade is contingent on a putative 25-amino-acid loop that is exposed to the outside of the bacterial cells.

The PagN protein of Salmonella enterica serovar Typhimurium is an adhesin and invasin.

BACKGROUND: The pagN gene of Salmonella enterica serovar Typhimurium is a PhoP-regulated gene that is up-regulated during growth within macrophages and in vivo in murine models of infection. The PagN protein displays similarity to the Hek and Tia invasins/adhesins of Escherichia coli. Thus far no function has been ascribed to the PagN protein. RESULTS: Here we show that the outer membrane located PagN protein mediates agglutination of red blood cells and that this can be masked by LPS. When expressed in Escherichia coli the PagN protein supports adhesion to and invasion of mammalian cells in a manner that is dependent on cytoskeletal rearrangements. S. enterica sv Typhimurium pagN mutants display a reduction in adhesion to and invasion of epithelial cells. Finally, we demonstrate that over-expression of PagN in a SPI-1 mutant can partially compensate for the lack of a functional invasasome. CONCLUSION: PagN is an outer membrane protein that may contribute to the virulence of S. Typhimurium. This protein is a haemagglutinin and contributes to the adherence to mammalian cells. In addition, PagN can mediate high-level invasion of CHO-K1 cells. Previously,pagN mutants have been shown to be less competitive in vivo and thus this may be due to their lessened ability to interact with mammalian cells. Finally PagN can be added to an ever-growing repertoire of factors that contribute to the pathogenesis of Salmonella.

Silver nanoparticles as a medical device in healthcare settings: a five-step approach for candidate screening of coating agents.

Silver nanoparticle-based antimicrobials can promote a long lasting bactericidal effect without detrimental toxic side effects. However, there is not a clear and complete protocol to define and relate the properties of the particles (size, shape, surface charge, ionic content) with their specific activity. In this paper, we propose an effective multi-step approach for the identification of a 'purpose-specific active applicability window' to maximize the antimicrobial activity of medical devices containing silver nanoparticles (Ag NPs) (such as surface coaters), minimizing any consequent risk for human health (safety by design strategy). The antimicrobial activity and the cellular toxicity of four types of Ag NPs, differing in their coating composition and concentration have been quantified. Through the implementation of flow-field flow fractionation, Ag NPs have been characterized in terms of metal release, size and shape. The particles are fractionated in the process while being left unmodified, allowing for the identification of biological particle-specific contribution. Toxicity and inflammatory response in vitro have been assessed on human skin models, while antimicrobial activity has been monitored with both non-pathogenic and pathogenic Escherichia coli. The main benefit associated with such approach is the comprehensive assessment of the maximal effectiveness of candidate nanomaterials, while simultaneously indexing their properties against their safety.

The Hek outer membrane protein of Escherichia coli is an auto-aggregating adhesin and invasin.

Escherichia coli is the principal gram-negative causative agent of sepsis and meningitis in neonates. The pathogenesis of meningitis due to E. coli K1 involves mucosal colonization, transcytosis of epithelial cells, survival in the blood stream and eventually invasion of the meninges. The latter two aspects have been well characterized at a molecular level in the last decade. Less is known about the early stages of pathogenesis, i.e. adhesion to and invasion of gastrointestinal cells. Here, the characterization of the Hek protein is reported, which is expressed by neonatal meningitic E. coli (NMEC) and is localized to the outer membrane. It is demonstrated that this protein can cause agglutination of red blood cells and can mediate autoaggregation. Escherichia coli expressing this protein can adhere to and invade epithelial cells. So far, this is the first outer membrane protein in NMEC to be directly implicated in epithelial cell invasion.

A molecular Swiss army knife: OmpA structure, function and expression.

The OmpA outer membrane protein of Escherichia coli and other enterobacteria is a multifaceted protein. This protein is expressed to very high levels and ompA is tightly regulated at the posttranscriptional level. It can function as an adhesin and invasin, participate in biofilm formation, act as both an immune target and evasin, and serves as a receptor for several bacteriophages. Many of these properties are due to four short protein loops that emanate from the protein to the outside of the cell. Herein it is described how the structure of this protein relates to its many functions.

Identification of a novel sequence type of Escherichia coli as the causative agent of pyelonephritis and bloodstream infection.

INTRODUCTION: Globally, extra-intestinal pathogenic Escherichia coli are one of the predominant causative agents of bacteraemia. CASE PRESENTATION: This case report outlines a presentation of community-acquired pyelonephritis and secondary bloodstream infection in an 81-year-old man. Laboratory investigations revealed that the causative isolate was a multi-drug-resistant E. coli of a novel multi-locus sequence type. This sequence type (ST) was designated ST-458 and was most closely related to the globally prevalent ST-131 lineage. CONCLUSION: This is the first report of a novel E. coli ST, ST-458, which caused pyelonephritis and bacteraemia.

Characterization of Escherichia coli bloodstream isolates associated with mortality.

Extra-intestinal pathogenic Escherichia coli (ExPEC) are the predominant cause of Gramnegative bloodstream infections. In this study, 20 E. coli isolates that were the causative agents of bacteraemia and subsequent mortality were characterized. Whole-genome sequencing was used to define the predominant sequence types (ST) among the isolates and to identify virulence factors associated with pathogenicity of ExPEC. The ability of the isolates to resist killing by both serum and polymorphonuclear leukocytes (PMNLs) was also assessed. In line with global trends, ST131 occurred most frequently among the bloodstream isolates and all isolates of this sequence type were multidrug resistant. Other common STs included ST73 and ST69. All isolates encoded multiple virulence factors across a range of categories, including factors involved in adhesion, immune evasion, iron acquisition and synthesis of toxins. None of these factors could be associated with serum and neutrophil resistance. The majority of isolates were resistant to the bactericidal action of serum and PMNLs, and most of those that were sensitive were isolated from patients with compromised immunity.

miR-CATCH: microRNA capture affinity technology.

Several experimental methods exist to explore the microRNA (miRNA) regulome. These methods almost exclusively focus on multiple targets bound to a single, or perhaps a few miRNAs of interest. Here, we describe a microRNA capture affinity technology (miR-CATCH) which uses an affinity capture oligonucleotide to co-purify a single target messenger RNA (mRNA) together with all its endogenously bound miRNAs. This bench-top method is similar to RNA immunoprecipitation (RIP) and provides an experimental alternative to computational miRNA target prediction.

Snap denaturation reveals dimerization by AraC-like protein Rns.

Here we show that the Rns regulator of Escherichia coli dimerises in vivo and in vitro. Furthermore, we demonstrate that Rns forms aggregates in vitro and describe a methodology to ameliorate aggregation thus permitting the analysis of Rns by cross-linking.

The PagN protein mediates invasion via interaction with proteoglycan.

Heparan sulphate proteoglycans are major components of the mammalian cell membrane. Here we show that PagN of Salmonella enterica serovar Typhimurium utilizes heparinated proteoglycan to successfully invade mammalian cells. Mutants defective in the production of the outer membrane protein PagN displayed similar levels of invasiveness of glycosylation-deficient pgsA-745 cells in comparison with wild-type Salmonella. Furthermore, pgsA-745 cells were invaded c. 400-fold less efficiently than CHO-K1 cells by Escherichia coli expressing PagN. PagN is likely to interact with heparinated proteoglycan as heparin could inhibit PagN-mediated invasion in a dose-dependent manner. Finally, we show, by deletion analysis, that all four extracellular loops of PagN are crucial for invasion of mammalian cells.

DNA supercoiling and the Lrp protein determine the directionality of fim switch DNA inversion in Escherichia coli K-12.

Site-specific recombinases of the integrase family usually require cofactors to impart directionality in the recombination reactions that they catalyze. The FimB integrase inverts the Escherichia coli fim switch (fimS) in the on-to-off and off-to-on directions with approximately equal efficiency. Inhibiting DNA gyrase with novobiocin caused inversion to become biased in the off-to-on direction. This directionality was not due to differential DNA topological distortion of fimS in the on and off phases by the activity of its resident P(fimA) promoter. Instead, the leucine-responsive regulatory (Lrp) protein was found to determine switching outcomes. Knocking out the lrp gene or abolishing Lrp binding sites 1 and 2 within fimS completely reversed the response of the switch to DNA relaxation. Inactivation of either Lrp site alone resulted in mild on-to-off bias, showing that they act together to influence the response of the switch to changes in DNA supercoiling. Thus, Lrp is not merely an architectural element organizing the fim invertasome, it collaborates with DNA supercoiling to determine the directionality of the DNA inversion event.

TLR-induced inflammation in cystic fibrosis and non-cystic fibrosis airway epithelial cells.

Cystic fibrosis (CF) is a genetic disease characterized by severe neutrophil-dominated airway inflammation. An important cause of inflammation in CF is Pseudomonas aeruginosa infection. We have evaluated the importance of a number of P. aeruginosa components, namely lipopeptides, LPS, and unmethylated CpG DNA, as proinflammatory stimuli in CF by characterizing the expression and functional activity of their cognate receptors, TLR2/6 or TLR2/1, TLR4, and TLR9, respectively, in a human tracheal epithelial line, CFTE29o(-), which is homozygous for the DeltaF508 CF transmembrane conductance regulator mutation. We also characterized TLR expression and function in a non-CF airway epithelial cell line 16HBE14o(-). Using RT-PCR, we demonstrated TLR mRNA expression. TLR cell surface expression was assessed by fluorescence microscopy. Lipopeptides, LPS, and unmethylated CpG DNA induced IL-8 and IL-6 protein production in a time- and dose-dependent manner. The CF and non-CF cell lines were largely similar in their TLR expression and relative TLR responses. ICAM-1 expression was also up-regulated in CFTE29o(-) cells following stimulation with each agonist. CF bronchoalveolar lavage fluid, which contains LPS, bacterial DNA, and neutrophil elastase (a neutrophil-derived protease that can activate TLR4), up-regulated an NF-kappaB-linked reporter gene and increased IL-8 protein production in CFTE29o(-) cells. This effect was abrogated by expression of dominant-negative versions of MyD88 or Mal, key signal transducers for TLRs, thereby implicating them as potential anti-inflammatory agents for CF.