PSF is an IbeA-binding protein contributing to meningitic Escherichia coli K1 invasion of human brain microvascular endothelial cells

The IbeA protein from adherent invasive Escherichia coli is a flavoprotein sharing structural homology with FAD-dependent oxidoreductases

Invasion of brain endothelium protein A (IbeA) is a virulence factor specific to pathogenic Escherichia coli. Originally identified in the K1 strain causing neonatal meningitis, it was more recently found in avian pathogenic Escherichia coli (APEC) and adherent invasive Escherichia coli (AIEC). In these bacteria, IbeA facilitates host cell invasion and intracellular survival, in particular, under harsh conditions like oxidative stress. Furthermore, IbeA from AIEC contributes to intramacrophage survival and replication, thus enhancing the inflammatory response within the intestine. Therefore, this factor is a promising drug target for anti-AIEC strategies in the context of Crohn's disease. Despite such an important role, the biological function of IbeA remains largely unknown. In particular, its exact nature and cellular localization, i.e., membrane-bound invasin versus cytosolic factor, are still of debate. Here, we developed an efficient protocol for recombinant expression of IbeA under native conditions and demonstrated that IbeA from AIEC is a soluble, homodimeric flavoprotein. Using mass spectrometry and tryptophan fluorescence measurements, we further showed that IbeA preferentially binds flavin adenine dinucleotide (FAD), with an affinity in the one-hundred nanomolar range and optimal binding under reducing conditions. 3D-modeling with AlphaFold revealed that IbeA shares strong structural homology with FAD-dependent oxidoreductases. Finally, we used ligand docking, mutational analyses, and molecular dynamics simulations to identify the FAD binding pocket within IbeA and characterize possible conformational changes occurring upon ligand binding. Overall, we suggest that the role of IbeA in the survival of AIEC within host cells, notably macrophages, is linked to modulation of redox processes.

Extraintestinal Pathogenic Escherichia coli: Virulence Factors and Antibiotic Resistance

The One Health approach emphasizes the importance of antimicrobial resistance (AMR) as a major concern both in public health and in food animal production systems. As a general classification, E. coli can be distinguished based on the ability to cause infection of the gastrointestinal system (IPEC) or outside of it (ExPEC). Among the different pathogens, E. coli are becoming of great importance, and it has been suggested that ExPEC may harbor resistance genes that may be transferred to pathogenic or opportunistic bacteria. ExPEC strains are versatile bacteria that can cause urinary tract, bloodstream, prostate, and other infections at non-intestinal sites. In this context of rapidly increasing multidrug-resistance worldwide and a diminishingly effective antimicrobial arsenal to tackle resistant strains. ExPEC infections are now a serious public health threat worldwide. However, the clinical and economic impact of these infections and their optimal management are challenging, and consequently, there is an increasing awareness of the importance of ExPECs amongst healthcare professionals and the general public alike. This review aims to describe pathotype characteristics of ExPEC to increase our knowledge of these bacteria and, consequently, to increase our chances to control them and reduce the risk for AMR, following a One Health approach.

Salmonella and Antimicrobial Resistance in Wild Rodents-True or False Threat?

Transmission of pathogenic and resistant bacteria from wildlife to the bacterial gene pool in nature affects the ecosystem. Hence, we studied intestine content of five wild rodent species: the yellow-necked wood mouse (Apodemus flavicollis, n = 121), striped field mouse (Apodemus agrarius, n = 75), common vole (Microtus arvalis, n = 37), bank vole (Myodes glareolus, n = 3), and house mouse (Mus musculus, n = 1) to assess their potential role as an antimicrobial resistance (AMR) and Salmonella vector. The methods adopted from official AMR monitoring of slaughtered animals were applied and supplemented with colistin resistance screening. Whole-genome sequencing of obtained bacteria elucidated their epidemiological relationships and zoonotic potential. The study revealed no indications of public health relevance of wild rodents from the sampled area in Salmonella spread and their limited role in AMR dissemination. Of 263 recovered E. coli, the vast majority was pan-susceptible, and as few as 5 E. coli showed any resistance. In four colistin-resistant strains neither the known mcr genes nor known mutations in pmr genes were found. One of these strains was tetracycline-resistant due to tet(B). High diversity of virulence factors (n = 43) noted in tested strains including ibeA, cdtB, air, eilA, astA, vat, pic reported in clinically relevant types of enteric E. coli indicate that rodents may be involved in the ecological cycle of these bacteria. Most of the strains represented unique sequence types and ST10805, ST10806, ST10810, ST10824 were revealed for the first time, showing genomic heterogeneity of the strains. The study broadened the knowledge on phylogenetic diversity and structure of the E. coli population in wild rodents.

The role of major virulence factors and pathogenicity of adherent-invasive Escherichia coli in patients with Crohn's disease

Inflammatory bowel disease (IBD) is a term that describes Crohn's disease (CD) and ulcerative colitis (UC), and these two conditions are characterised by chronic inflammation of the gastrointestinal tract. Dysbiosis of intestinal microbiota has been consistently linked to patients with IBD. In the last two decades, the progressive implication of adherent-invasive Escherichia coli (AIEC) pathogenesis in patients with CD has been increasing. Here we discuss recent findings that indicate the role and mechanisms of AIEC in IBD. We also highlight AIEC virulence factor genes and mechanisms that suggest an important role in the severity of inflammation in CD patients. Finally, we emphasise data on the prevalence of AIEC in CD patients.

Inhibitor discovery for the E. coli meningitis virulence factor IbeA from homology modeling and virtual screening

Escherichia coli (E. coli) K1 is the most common Gram-negative bacteria cause of neonatal meningitis. The penetration of E. coli through the blood-brain barrier is a key step of the meningitis pathogenesis. A host receptor protein, Caspr1, interacts with the E. coli virulence factor IbeA and thus facilitates bacterial penetration through the blood-brain barrier. Based on this result, we have now predicted the binding pattern between Caspr1 and IbeA by an integrated computational protocol. Based on the predicted model, we have identified a putative molecular binding pocket in IbeA, that directly bind with Caspr1. This evidence indicates that the IbeA (229-343aa) region might play a key role in mediating the bacteria invasion. Virtual screening with the molecular model was conducted to search for potential inhibitors from 213,279 commercially available chemical compounds. From the top 50 identified compounds, 9 demonstrated a direct binding ability to the residues within the Caspr1 binding site on IbeA. By using human brain microvascular endothelial cells (hBMEC) with E. coli strain RS218, four molecules were characterized that significantly attenuated the bacteria invasions at concentrations devoid of cell toxicity. Our study provides useful structural information for understanding the pathogenesis of neonatal meningitis, and have identified drug-like compounds that could be used to develop effective anti-meningitis agents.

Vimentin, a Novel NF-κB Regulator, Is Required for Meningitic Escherichia coli K1-Induced Pathogen Invasion and PMN Transmigration across the Blood-Brain Barrier

BACKGROUND

NF-κB activation, pathogen invasion, polymorphonuclear leukocytes (PMN) transmigration (PMNT) across the blood-brain barrier (BBB) are the pathogenic triad hallmark features of bacterial meningitis, but the mechanisms underlying these events remain largely unknown. Vimentin, which is a novel NF-κB regulator, is the primary receptor for the major Escherichia coli K1 virulence factor IbeA that contributes to the pathogenesis of neonatal bacterial sepsis and meningitis (NSM). We have previously shown that IbeA-induced NF-κB signaling through its primary receptor vimentin as well as its co-receptor PTB-associated splicing factor (PSF) is required for pathogen penetration and leukocyte transmigration across the BBB. This is the first in vivo study to demonstrate how vimentin and related factors contributed to the pathogenic triad of bacterial meningitis.

METHODOLOGY/PRINCIPAL FINDINGS

The role of vimentin in IbeA+ E. coli K1-induced NF-κB activation, pathogen invasion, leukocyte transmigration across the BBB has now been demonstrated by using vimentin knockout (KO) mice. In the in vivo studies presented here, IbeA-induced NF-κB activation, E. coli K1 invasion and polymorphonuclear neutrophil (PMN) transmigration across the BBB were significantly reduced in Vim-/- mice. Decreased neuronal injury in the hippocampal dentate gyrus was observed in Vim-/- mice with meningitis. The major inflammatory regulator α7 nAChR and several signaling molecules contributing to NF-κB activation (p65 and p-CamKII) were significantly reduced in the brain tissues of the Vim-/- mice with E. coli meningitis. Furthermore, Vim KO resulted in significant reduction in neuronal injury and in α7 nAChR-mediated calcium signaling.

CONCLUSION/SIGNIFICANCE

Vimentin, a novel NF-κB regulator, plays a detrimental role in the host defense against meningitic infection by modulating the NF-κB signaling pathway to increase pathogen invasion, PMN recruitment, BBB permeability and neuronal inflammation. Our findings provide the first evidence for Vim-dependent mechanisms underlying the pathogenic triad of bacterial meningitis.

The DBHS proteins SFPQ, NONO and PSPC1: a multipurpose molecular scaffold

Nuclear proteins are often given a concise title that captures their function, such as 'transcription factor,' 'polymerase' or 'nuclear-receptor.' However, for members of the Drosophila behavior/human splicing (DBHS) protein family, no such clean-cut title exists. DBHS proteins are frequently identified engaging in almost every step of gene regulation, including but not limited to, transcriptional regulation, RNA processing and transport, and DNA repair. Herein, we present a coherent picture of DBHS proteins, integrating recent structural insights on dimerization, nucleic acid binding modalities and oligomerization propensity with biological function. The emerging paradigm describes a family of dynamic proteins mediating a wide range of protein-protein and protein-nucleic acid interactions, on the whole acting as a multipurpose molecular scaffold. Overall, significant steps toward appreciating the role of DBHS proteins have been made, but we are only beginning to understand the complexity and broader importance of this family in cellular biology.

The IbeA invasin of adherent-invasive Escherichia coli mediates interaction with intestinal epithelia and macrophages

Adherent-invasive Escherichia coli (AIEC) pathogroup isolates are a group of isolates from the intestinal mucosa of Crohn's disease patients that can invade intestinal epithelial cells (IECs) or macrophages and survive and/or replicate within. We have identified the ibeA gene in the genome of AIEC strain NRG857c and report the contribution of IbeA to the interaction of AIEC with IECs and macrophages and colonization of the mouse intestine. An ibeA deletion mutant strain (NRG857cΔibeA) was constructed, and the in vitro effect on AIEC adhesion and invasion of nonpolarized and polarized Caco-2 cells, the adhesion and transcytosis of M-like cells, the intracellular survival in THP-1 macrophages, and the contribution to intestinal colonization of the CD-1 murine model of infection were evaluated. A significant reduction in invasion was observed with the ibeA mutant in Caco-2 and M-like cells, whereas adhesion was not affected. Complementation of the mutant reestablished Caco-2 invasive phenotype to wild-type levels. Reduction in invasion did not significantly affect transcytosis through M-like cells at early time points. The absence of ibeA significantly affected AIEC intramacrophage survival up to 24 h postinfection. No significant changes associated with IbeA were found in AIEC colonization across the murine gastrointestinal tract, but a slight reduction of gamma interferon was observed in the ceca of mice infected with the ibeA mutant. In addition, a decrease in the pathology scores was observed in the ilea and ceca of mice infected with the ibeA mutant. Our data support the function of IbeA in the AIEC invasion process, macrophage survival, and inflammatory response in the murine intestine.

Pathogens penetrating the central nervous system: infection pathways and the cellular and molecular mechanisms of invasion

The brain is well protected against microbial invasion by cellular barriers, such as the blood-brain barrier (BBB) and the blood-cerebrospinal fluid barrier (BCSFB). In addition, cells within the central nervous system (CNS) are capable of producing an immune response against invading pathogens. Nonetheless, a range of pathogenic microbes make their way to the CNS, and the resulting infections can cause significant morbidity and mortality. Bacteria, amoebae, fungi, and viruses are capable of CNS invasion, with the latter using axonal transport as a common route of infection. In this review, we compare the mechanisms by which bacterial pathogens reach the CNS and infect the brain. In particular, we focus on recent data regarding mechanisms of bacterial translocation from the nasal mucosa to the brain, which represents a little explored pathway of bacterial invasion but has been proposed as being particularly important in explaining how infection with Burkholderia pseudomallei can result in melioidosis encephalomyelitis.

The RNA/DNA-binding protein PSF relocates to cell membrane and contributes cells' sensitivity to antitumor drug, doxorubicin

Cell surface proteins play an important role in multidrug resistance (MDR). However, the identification involving chemoresistant features for cell surface proteins is a challenge. To identify potential cell membrane markers in hematologic cancer MDR, we used a cell- and antibody-based strategy of subtractive immunization coupled with cell surface comparative screening of leukemia cell lines from sensitive HL60 and resistant HL60/DOX cells. Fifty one antibodies that recognized the cell surface proteins expressed differently between the two cell lines were generated. One of them, the McAb-5D12 not only recognizes its antigen but also block its function. Comparative analysis of immunofluorescence, flow cytometry, and mass spectrum analysis validated that the membrane antigen of McAb-5D12 is a nucleoprotein-polypyrimidine tract binding protein associated splicing factor, PSF. Our results identified that PSF overexpressed on the membrane of sensitive cells compared with resistant cells and its relocation from the nuclear to the cell surface was common in hematological malignancy cell lines and marrow of leukemia patients. Furthermore, we found that cell surface PSF contributed to cell sensitivity by inhibiting cell proliferation. The results represent a novel and potentially useful biomarker for MDR prediction. The strategy enables the correlation of expression levels and functions of cell surface protein with some cell-drug response traits by using antibodies.

New role for the ibeA gene in H2O2 stress resistance of Escherichia coli

ibeA is a virulence factor found in some extraintestinal pathogenic Escherichia coli (ExPEC) strains from the B2 phylogenetic group and particularly in newborn meningitic and avian pathogenic strains. It was shown to be involved in the invasion process of the newborn meningitic strain RS218. In a previous work, we showed that in the avian pathogenic E. coli (APEC) strain BEN2908, isolated from a colibacillosis case, ibeA was rather involved in adhesion to eukaryotic cells by modulating type 1 fimbria synthesis (M. A. Cortes et al., Infect. Immun. 76:4129-4136, 2008). In this study, we demonstrate a new role for ibeA in oxidative stress resistance. We showed that an ibeA mutant of E. coli BEN2908 was more sensitive than its wild-type counterpart to H(2)O(2) killing. This phenotype was also observed in a mutant deleted for the whole GimA genomic region carrying ibeA and might be linked to alterations in the expression of a subset of genes involved in the oxidative stress response. We also showed that RpoS expression was not altered by the ibeA deletion. Moreover, the transfer of an ibeA-expressing plasmid into an E. coli K-12 strain, expressing or not expressing type 1 fimbriae, rendered it more resistant to an H(2)O(2) challenge. Altogether, these results show that ibeA by itself is able to confer increased H(2)O(2) resistance to E. coli. This feature could partly explain the role played by ibeA in the virulence of pathogenic strains.

Vimentin and PSF act in concert to regulate IbeA+ E. coli K1 induced activation and nuclear translocation of NF-κB in human brain endothelial cells

BACKGROUND

IbeA-induced NF-κB signaling through its primary receptor vimentin as well as its co-receptor PSF is required for meningitic E. coli K1 penetration and leukocyte transmigration across the blood-brain barrier (BBB), which are the hallmarks of bacterial meningitis. However, it is unknown how vimentin and PSF cooperatively contribute to IbeA-induced cytoplasmic activation and nuclear translocation of NF-κB, which are required for bacteria-mediated pathogenicities.

METHODOLOGY/PRINCIPAL FINDINGS

IbeA-induced E. coli K1 invasion, polymorphonuclear leukocyte (PMN) transmigration and IKK/NF-κB activation are blocked by Caffeic acid phenethyl ester (CAPE), an inhibitor of NF-κB. IKKα/β phosphorylation is blocked by ERK inhibitors. Co-immunoprecipitation analysis shows that vimentin forms a complex with IκB, NF-κB and tubulins in the resting cells. A dissociation of this complex and a simultaneous association of PSF with NF-κB could be induced by IbeA in a time-dependent manner. The head domain of vimentin is required for the complex formation. Two cytoskeletal components, vimentin filaments and microtubules, contribute to the regulation of NF-κB. SiRNA-mediated knockdown studies demonstrate that IKKα/β phosphorylation is completely abolished in HBMECs lacking vimentin and PSF. Phosphorylation of ERK and nuclear translocation of NF-κB are entirely dependent on PSF. These findings suggest that vimentin and PSF cooperatively contribute to IbeA-induced cytoplasmic activation and nuclear translocation of NF-κB activation. PSF is essential for translocation of NF-κB and ERK to the nucleus.

CONCLUSION/SIGNIFICANCE

These findings reveal previously unappreciated facets of the IbeA-binding proteins. Cooperative contributions of vimentin and PSF to IbeA-induced cytoplasmic activation and nuclear translocation of NF-κB may represent a new paradigm in pathogen-induced signal transduction and lead to the development of novel strategies for the prevention and treatment of bacterial meningitis.

Involvement of IbeA in meningitic Escherichia coli K1-induced polymorphonuclear leukocyte transmigration across brain endothelial cells

Transmigration of neutrophil [polymorphonuclear neutrophil (PMN)] across the blood-brain barrier (BBB) is a critical event in the pathogenesis of bacterial meningitis. We have shown that IbeA is able to induce meningitic Escherichia coli invasion of brain microvascular endothelial cells (BMECs), which constitutes the BBB. In this report, we provide evidence that IbeA and its receptor, vimentin, play a key role in E. coli-induced PMN transmigration across BMEC. In vitro and in vivo studies indicated that the ibeA-deletion mutant ZD1 was significantly less active in stimulating PMN transmigration than the parent strain E44. ZD1 was fully complemented by the ibeA gene and its product. E. coli-induced PMN transmigration was markedly inhibited by withaferin A, a dual inhibitor of vimentin and proteasome. These cellular effects were significantly stimulated and blocked by overexpression of vimentin and its head domain deletion mutant in human BMEC, respectively. Our studies further demonstrated that IbeA-induced PMN migration was blocked by bortezomib, a proteasomal inhibitor and correlated with upregulation of endothelial ICAM-1 and CD44 expression through proteasomal regulation of NFκB activity. Taken together, our data suggested that IbeA and vimentin contribute to E. coli K1-stimulated PMN transendothelial migration that is correlated with upregulation of adhesion molecule expression at the BBB.

Effects of ibeA deletion on virulence and biofilm formation of avian pathogenic Escherichia coli

The ibeA gene is located on a genomic island, GimA, which is involved in the pathogenesis of neonatal meningitis Escherichia coli (NMEC) and avian pathogenic E. coli (APEC). The prevalence of ibeA in the APEC collection in China was investigated, and 20 of 467 strains (4.3%) were positive. In addition, analysis of the association of the E. coli reference (ECOR) groups with positive strains revealed that ibeA was linked to group B2. The ibeA gene in DE205B was analyzed and compared to those of APEC and NMEC, which indicated that the specificity of ibeA was not consistent along pathotypes. The invasion of chicken embryo fibroblast DF-1 cells by APEC DE205B and RS218 was observed, which suggested that DF-1 cells could be a model to study the mechanism of APEC invasion. The inactivation of ibeA in APEC DE205B led to the reduced capacity to invade DF-1 cells, defective virulence in vivo, and decreased biofilm formation compared to the wild-type strain. In addition, strain AAEC189 expressing ibeA exhibited enhanced invasion capacity and biofilm formation. The results of the quantitative real-time reverse transcription-PCR (qRT-PCR) analysis and animal system infection experiments indicated that the loss of ibeA decreased the colonization and proliferation capacities of APEC in the brain during system infection.

Complete genome sequence of Crohn's disease-associated adherent-invasive E. coli strain LF82

BACKGROUND

Ileal lesions of Crohn's disease (CD) patients are abnormally colonized by pathogenic adherent-invasive Escherichia coli (AIEC) able to invade and to replicate within intestinal epithelial cells and macrophages.

PRINCIPAL FINDINGS

We report here the complete genome sequence of E. coli LF82, the reference strain of adherent-invasive E. coli associated with ileal Crohn's disease. The LF82 genome of 4,881,487 bp total size contains a circular chromosome with a size of 4,773,108 bp and a plasmid of 108,379 bp. The analysis of predicted coding sequences (CDSs) within the LF82 flexible genome indicated that this genome is close to the avian pathogenic strain APEC_01, meningitis-associated strain S88 and urinary-isolated strain UTI89 with regards to flexible genome and single nucleotide polymorphisms in various virulence factors. Interestingly, we observed that strains LF82 and UTI89 adhered at a similar level to Intestine-407 cells and that like LF82, APEC_01 and UTI89 were highly invasive. However, A1EC strain LF82 had an intermediate killer phenotype compared to APEC-01 and UTI89 and the LF82 genome does not harbour most of specific virulence genes from ExPEC. LF82 genome has evolved from those of ExPEC B2 strains by the acquisition of Salmonella and Yersinia isolated or clustered genes or CDSs located on pLF82 plasmid and at various loci on the chromosome.

CONCLUSION

LF82 genome analysis indicated that a number of genes, gene clusters and pathoadaptative mutations which have been acquired may play a role in virulence of AIEC strain LF82.

Vimentin-mediated signalling is required for IbeA+ E. coli K1 invasion of human brain microvascular endothelial cells

IbeA in meningitic Escherichia coli K1 strains has been described previously for its role in invasion of BMECs (brain microvascular endothelial cells). Vimentin was identified as an IbeA-binding protein on the surface of HBMECs (human BMECs). In the present study, we demonstrated that vimentin is a primary receptor required for IbeA+ E. coli K1-induced signalling and invasion of HBMECs, on the basis of the following observations. First, E44 (IbeA+ E. coli K1 strain) invasion was blocked by vimentin inhibitors (withaferin A and acrylamide), a recombinant protein containing the vimentin head domain and an antibody against the head domain respectively. Secondly, overexpression of GFP (green fluorescent protein)-vimentin and GFP-VDM (vimentin head domain deletion mutant) significantly increased and decreased bacterial invasion respectively. Thirdly, bacterial invasion was positively correlated with phosphorylation of vimentin at Ser82 by CaMKII (Ca2+/calmodulin-dependent protein kinase II) and IbeA+ E. coli-induced phosphorylation of ERK (extracellular-signal-regulated kinase). Blockage of CaMKII by KN93 and inhibition of ERK1/2 phosphorylation by PD098059 resulted in reduced IbeA+ E. coli invasion. Fourthly, IbeA+ E. coli and IbeA-coated beads induced the clustering of vimentin that was correlated with increased entry of bacteria and beads. Lastly, IbeA+ E. coli K1 invasion was inhibited by lipid-raft-disrupting agents (filipin and nystatin) and caveolin-1 siRNA (small interfering RNA), suggesting that caveolae/lipid rafts are signalling platforms for inducing IbeA-vimentin-mediated E. coli invasion of HBMECs. Taken together, the present studies suggest that a dynamic and function-related interaction between IbeA and its primary receptor vimentin at HBMEC membrane rafts leads to vimentin phosphorylation and ERK-mediated signalling, which modulate meningitic E. coli K1 invasion.

The gut immune barrier and the blood-brain barrier: are they so different?

In order to protect itself from a diverse set of environmental pathogens and toxins, the body has developed a number of barrier mechanisms to limit the entry of potential hazards. Here, we compare two such barriers: the gut immune barrier, which is the primary barrier against pathogens and toxins ingested in food, and the blood-brain barrier, which protects the central nervous system from pathogens and toxins in the blood. Although each barrier provides defense in very different environments, there are many similarities in their mechanisms of action. In both cases, there is a physical barrier formed by a cellular layer that tightly regulates the movement of ions, molecules, and cells between two tissue spaces. These barrier cells interact with different cell types, which dynamically regulate their function, and with a different array of immune cells that survey the physical barrier and provide innate and adaptive immunity.

Inactivation of ibeA and ibeT results in decreased expression of type 1 fimbriae in extraintestinal pathogenic Escherichia coli strain BEN2908

IbeA in extraintestinal pathogenic Escherichia coli (ExPEC) strains was previously described for its role in invasion. Here we investigated the role of IbeA and IbeT, encoded by a gene located downstream of ibeA, in the adhesion of the avian ExPEC strain BEN2908 to human brain microvascular endothelial cells (HBMEC). The DeltaibeA mutant was less adhesive to HBMEC than the wild-type strain BEN2908 was. Because strain BEN2908 also expresses type 1 fimbriae, we measured the adhesion specifically due to IbeA by comparing the adhesive properties of a Deltafim derivative of strain BEN2908 to those of a double Deltafim DeltaibeA mutant. No differences were observed, indicating that the reduction of adhesion in BEN2908 DeltaibeA could be due to a decrease in type 1 fimbria expression. We indeed showed that the decreased adhesion of BEN2908 DeltaibeA was correlated with a decrease in type 1 fimbria expression. Accordingly, more bacteria had a fim promoter orientated in the off position in a culture of BEN2908 DeltaibeA than in a culture of BEN2908. Expression of fimB and fimE, two genes encoding recombinases participating in controlling the orientation of the fim promoter, was decreased in BEN2908 DeltaibeA. A reduction of type 1 fimbria expression due to a preferential orientation of the fim promoter in the off position was also seen in an ibeT mutant of strain BEN2908. We finally suggest a role for IbeA and IbeT in modulating the expression of type 1 fimbriae through an as yet unknown mechanism.

Differential expression of iutA and ibeA in the early stages of infection by extra-intestinal pathogenic E. coli

Extraintestinal pathogenic Escherichia coli strains are responsible for a number of infections in humans and animals. Several ExPEC virulence genes have already been described such as iutA involved in iron acquisition and ibeA required for invasion of eukaryotic cells. In this study we used the chicken model to study the expression of iutA and ibeA by two ExPEC strains during growth of bacteria in LB medium and during the infection. Expression of iutA and ibeA were shown to be higher in stationary phase than in exponential phase in vitro. During infection, iutA expression was increased at least 50-fold in the airsac and in the lung 3, 6 and 24h. p.i. compared to in vitro grown bacteria. Expression of ibeA was increased 2.5-9-fold in the airsac in the early stages of the infection only. This is the first report analyzing quantitatively the expression of ExPEC virulence genes during the course of the infection. The model described could be useful to study the expression of other ExPEC virulence genes.

Involvement of Escherichia coli K1 ibeT in bacterial adhesion that is associated with the entry into human brain microvascular endothelial cells

IbeT is a downstream gene of the invasion determinant ibeA in the chromosome of a clinical isolate of Escherichia coli K1 strain RS218 (serotype 018:K1:H7). Both ibeT and ibeA are in the same operon. Our previous mutagenesis and complementation studies suggested that ibeT may coordinately contribute to E. coli K1 invasion with ibeA. An isogenic in-frame deletion mutant of ibeT has been made by chromosomal gene replacement with a recombinant suicide vector carrying a fragment with an ibeT internal deletion. The characteristics of the mutant in meningitic E. coli infection were examined in vitro [cell culture of human brain microvascular endothelial cells (HBMEC)] and in vivo (infant rat model of E. coli meningitis) in comparison with the parent strain. The ibeT deletion mutant was significantly less adhesive and invasive than its parent strain E. coli E44 in vitro, and the adhesion- and invasion-deficient phenotypes of the mutant can be complemented by the ibeT gene. Recombinant IbeT protein is able to block E. coli E44 invasion of HBMEC. Furthermore, the ibeT deletion mutant is less capable of colonizing intestine and less virulent in bacterial translocation across the blood-brain barrier (BBB) than its parent E. coli E44 in vivo. These data suggest that ibeT-mediated E. coli K1 adhesion is associated with the bacterial invasion process.