Further characterization of Escherichia coli brain microvascular endothelial cell invasion gene ibeA by deletion, complementation, and protein expression

Advancing Understanding of Escherichia coli Pathogenicity in Preterm Neonatal Sepsis

Neonatal sepsis is a major cause of mortality in preterm infants, with Escherichia coli as one of the leading pathogens. Few studies have examined the interplay between virulence factors, resistance profiles, phylogroups, and clinical outcomes in this population. We analyzed 52 E. coli strains isolated from 49 preterm neonates diagnosed with sepsis at a tertiary-level hospital in Mexico. Strains underwent phylogenetic classification, virulence gene profiling, and antimicrobial resistance testing. PFGE was used to assess genetic relatedness and outbreak clusters. Clinical data were correlated with molecular findings. Phylogroups A and B2 accounted for 46% of strains. Phylogroup A exhibited notable virulence, with high prevalence of the pathogenicity island described in virulent extra-intestinal E. coli strains (PAI), aerobactin siderophore receptor AerJ (iutA), and yersiniabactin siderophore receptor (fyuA) genes, alongside significant resistance profiles. PFGE identified two dominating branches. Branch A, comprising phylogroups A and B2, displayed high resistance and was prevalent in the neonatal intensive care unit. Branch C, with phylogroups A and D, showed less multidrug resistance but was significantly associated with maternal chorioamnionitis. This study redefines E. coli pathogenicity in neonatal sepsis, highlighting the virulence of traditionally non-pathogenic phylogroups. High virulence strains were associated with more severe outcomes. These findings underscore the need for enhanced strategies in targeted prevention, improved diagnostics, and tailored treatments for high-risk preterm populations.

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.

Insight on Bacterial Newborn Meningitis Using a Neurovascular-Unit-on-a-Chip

Understanding the pathogenesis of bacterial infections is critical for combatting them. For some infections, animal models are inadequate and functional genomic studies are not possible. One example is bacterial meningitis, a life-threatening infection with high mortality and morbidity. Here, we used the newly developed, physiologically relevant, organ-on-a-chip platform integrating the endothelium with neurons, closely mimicking in vivo conditions. Using high-magnification microscopy, permeability measurements, electrophysiological recordings, and immunofluorescence staining, we studied the dynamic by which the pathogens cross the blood-brain barrier and damage the neurons. Our work opens up possibilities for performing large-scale screens with bacterial mutant libraries for identifying the virulence genes involved in meningitis and determining the role of these genes, including various capsule types, in the infection process. These data are essential for understanding and therapy of bacterial meningitis. Moreover, our system offers possibilities for the study of additional infections-bacterial, fungal, and viral. IMPORTANCE The interactions of newborn meningitis (NBM) with the neurovascular unit are very complex and are hard to study. This work presents a new platform to study NBM in a system that enables monitoring of multicellular interactions and identifies processes that were not observed before.

OmpA is involved in the invasion of duck brain microvascular endothelial cells by Riemerella anatipestifer

Bacterial meningitis is a major cause of morbidity and mortality. Despite advances in antimicrobial chemotherapy, the disease remains detrimental to humans, livestock, and poultry. Riemerella anatipestifer is a gram-negative bacterium causing duckling serositis and meningitis. However, the virulence factors contributing to its binding and invasion of duck brain microvascular endothelial cells (DBMECs) and penetration of the blood-brain barrier (BBB) have never been reported. In this study, immortalized DBMECs were successfully generated and used as an in vitro-model of duck BBB. Furthermore, ompA gene deletion mutant of the pathogen and multiple complemented strains carrying the complete ompA gene and its truncated forms were constructed. Bacterial growth, invasion, and adhesion assays and animal experiments were performed. The results show that the OmpA protein of R. anatipestifer had no effect on bacterial growth and adhesion ability to DBMECs. The role of OmpA in the invasion of R. anatipestifer into DBMECs and duckling BBB was confirmed. The amino acids 230-242 of OmpA represents a key domain involved in R. anatipestifer invasion. In addition, another OmpA1164 protein constituted by the amino acids 102-488 within OmpA could function as a complete OmpA. The signal peptide sequence from amino acids 1-21 had no significant effect on OmpA functions. In conclusion, this study illustrated that OmpA is an important virulence factor mediating R. anatipestifer invasion of DBMECs and penetration of the duckling BBB.

Pan-genome wide association study of Glaesserella parasuis highlights genes associated with virulence and biofilm formation

Glaesserella parasuis is a gram-negative bacterium that causes fibrotic polyserositis and arthritis in pig, significantly affecting the pig industry. The pan-genome of G. parasuis is open. As the number of genes increases, the core and accessory genomes may show more pronounced differences. The genes associated with virulence and biofilm formation are also still unclear due to the diversity of G. parasuis. Therefore, we have applied a pan-genome-wide association study (Pan-GWAS) to 121 strains G. parasuis. Our analysis revealed that the core genome consists of 1,133 genes associated with the cytoskeleton, virulence, and basic biological processes. The accessory genome is highly variable and is a major cause of genetic diversity in G. parasuis. Furthermore, two biologically important traits (virulence, biofilm formation) of G. parasuis were studied via pan-GWAS to search for genes associated with the traits. A total of 142 genes were associated with strong virulence traits. By affecting metabolic pathways and capturing the host nutrients, these genes are involved in signal pathways and virulence factors, which are beneficial for bacterial survival and biofilm formation. This research lays the foundation for further studies on virulence and biofilm formation and provides potential new drug and vaccine targets against G. parasuis.

Clonal Lineages and Virulence Factors of Carbapenem Resistant E. coli in Alameda County, California, 2017-2019

The prevalence of carbapenem-resistant Enterobacterales (CRE) has been increasing since the year 2000 and is considered a serious public health threat according to the Centers for Disease Control and Prevention. Limited studies have genotyped Carbapenem-resistant Escherichia coli using whole genome sequencing to characterize the most common lineages and resistance and virulence genes. The aim of this study was to characterize sequence data from carbapenem-resistant E. coli isolates (n = 82) collected longitudinally by the Alameda County Public Health Laboratory (ACPHL) between 2017 and 2019. E. coli genomes were screened for antibiotic resistance genes (ARGs) and extraintestinal pathogenic E. coli virulence factor genes (VFGs). The carbapenem-resistant E. coli lineages were diverse, with 24 distinct sequence types (STs) represented, including clinically important STs: ST131, ST69, ST95, and ST73. All Ambler classes of Carbapenemases were present, with NDM-5 being most the frequently detected. Nearly all isolates (90%) contained genes encoding resistance to third-generation cephalosporins; bla_CTX-M genes were most common. The number of virulence genes present within pandemic STs was significantly higher than the number in non-pandemic lineages (p = 0.035). Virulence genes fimA (92%), trat (71%), kpsM (54%), and iutA (46%) were the most prevalent within the isolates. Considering the public health risk associated with CRE, these data enhance our understanding of the diversity of clinically important E. coli that are circulating in Alameda County, California.

Alpha7 Nicotinic Acetylcholine Receptor Antagonists Prevent Meningitic Escherichia coli-Induced Blood–Brain Barrier Disruptions by Targeting the CISH/JAK2/STAT5b Axis

Despite the availability of antibiotics over the last several decades, excessive antibiotic treatments for bacterial sepsis and meningitis (BSM) in children may result in several adverse outcomes. Hematogenous pathogens may directly induce permeability increases in human brain microvascular endothelial cells (HBMECs) and blood–brain barrier (BBB) dysfunctions. Our preliminary studies demonstrated that the alpha7 nicotinic acetylcholine receptor (α7nAChR) played an important role in the pathogenesis of BSM, accompanied by increasing cytokine-inducible SH2-containing protein (CISH) at the transcriptome level, but it has remained unclear how α7nAChR-CISH works mechanistically. The study aims to explore the underlying mechanism of α7nAChR and CISH during E. coli-induced BSM in vitro (HBMECs) and in vivo (α7nAChR-KO mouse). We found that in the stage of E. coli K1-induced BBB disruptions, α7nAChR functioned as the key regulator that affects the integrity of HBMECs by activating the JAK2–STAT5 signaling pathway, while CISH inhibited JAK2–STAT5 activation and exhibited protective effects against E. coli infection. Notably, we first validated that the expression of CISH could be regulated by α7nAChR in HBMECs. In addition, we determined the protective effects of MLA (methyllycaconitine citrate) and MEM (memantine hydrochloride) (functioning as α7nAChR antagonists) on infected HBMECs and suggested that the α7nAChR–CISH axis could explain the protective effects of the two small-molecule compounds on E. coli-induced HBMECs injuries and BBB disruptions. In conclusion, we dissected the α7nAChR/CISH/JAK2/STAT5 axis as critical for the pathogenesis of E. coli-induced brain microvascular leakage and BBB disruptions and provided novel evidence for the development of α7nAChR antagonists in the prevention of pediatric E. coli BSM.

Evaluation of the Pathogenic Potential of Escherichia coli Strains Isolated from Eye Infections

While primarily Gram-positive bacteria cause bacterial eye infections, several Gram-negative species also pose eye health risks. Currently, few studies have tried to understand the pathogenic mechanisms involved in E. coli eye infections. Therefore, this study aimed to establish the pathogenic potential of E. coli strains isolated from eye infections. Twenty-two strains isolated between 2005 and 2019 from patients with keratitis or conjunctivitis were included and submitted to traditional polymerase chain reactions (PCR) to define their virulence profile, phylogeny, clonal relationship, and sequence type (ST). Phenotypic assays were employed to determine hemolytic activity, antimicrobial susceptibility, and adhesion to human primary corneal epithelial cells (PCS-700-010). The phylogenetic results indicated that groups B2 and ST131 were the most frequent. Twenty-five virulence genes were found among our strains, with ecp, sitA, fimA, and fyuA being the most prevalent. Two strains presented a hemolytic phenotype, and resistance to ciprofloxacin and ertapenem was found in six strains and one strain, respectively. Regarding adherence, all but one strains adhered in vitro to corneal cells. Our results indicate significant genetic and virulence variation among ocular strains and point to an ocular pathogenic potential related to multiple virulence mechanisms.

Whole-genome sequencing-based phylogeny, antibiotic resistance, and invasive phenotype of Escherichia coli strains colonizing the cervix of women in preterm labor

BACKGROUND

Escherichia coli is a major neonatal pathogen and the leading cause of early-onset sepsis in preterm newborns. Maternal E. coli strains are transmitted to the newborn causing invasive neonatal disease. However, there is a lack of data regarding the phenotypic and genotypic characterization of E. coli strains colonizing pregnant women during labor.

METHODS

This prospective study performed at the University of Oklahoma Medical Center (OUHSC) from March 2014 to December 2015, aimed to investigate the colonization rate, and the phylogeny, antibiotic resistance traits, and invasive properties of E. coli strains colonizing the cervix of fifty pregnant women diagnosed with preterm labor (PTL). Molecular analyses including bacterial whole-genome sequencing (WGS), were performed to examine phylogenetic relationships among the colonizing strains and compare them with WGS data of representative invasive neonatal E. coli isolates. Phenotypic and genotypic antibiotic resistance traits were investigated. The bacteria's ability to invade epithelial cells in vitro was determined.

RESULTS

We recruited fifty women in PTL. Cervical samples yielded E. coli in 12 % (n=6). The mean gestational age was 32.5 (SD±3.19) weeks. None delivered an infant with E. coli disease. Phenotypic and genotypic antibiotic resistance testing did not overall demonstrate extensive drug resistance traits among the cervical E. coli isolates, however, one isolate was multi-drug resistant. The isolates belonged to five different phylogroups, and WGS analyses assigned each to individual multi-locus sequence types. Single nucleotide polymorphism-based comparisons of cervical E. coli strains with six representative neonatal E. coli bacteremia isolates demonstrated that only half of the cervical E. coli isolates were phylogenetically related to these neonatal invasive strains. Moreover, WGS comparisons showed that each cervical E. coli isolate had distinct genomic regions that were not shared with neonatal E. coli isolates. Cervical and neonatal E. coli isolates that were most closely related at the phylogenetic level had similar invasion capacity into intestinal epithelial cells. In contrast, phylogenetically dissimilar cervical E. coli strains were the least invasive among all isolates.

CONCLUSIONS

This pilot study showed that a minority of women in PTL were colonized in the cervix with E. coli, and colonizing strains were not phylogenetically uniformly representative of E. coli strains that commonly cause invasive disease in newborns. Larger studies are needed to determine the molecular characteristics of E. coli strains colonizing pregnant women associated with an increased risk of neonatal septicemia.

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.

Thickening of the walls of deep brain abscesses is associated with macrophage infiltration

The present study aimed to compare the thickness of brain abscesses in the deep and the superficial brain and to investigate the factors that influence the capsule of brain abscesses. The thickness of the brain abscess wall was evaluated on imaging. Bacteriological examination was performed on the abscess pus and wall, and immunohistochemical staining was used to count the number of macrophages. Kaplan-Meier curves were used to analyze overall survival. The results indicated that the wall of deep-brain abscesses was thicker than that of superficial abscesses. There was a difference in the extent of macrophage infiltration of deep- and superficial-brain abscess walls, and differences in the extent of macrophage infiltration in the wall of brain abscesses caused by various microorganisms were statistically significant. Of note, among the brain abscesses caused by Staphylococcus, the extent of macrophage/microglia infiltration and the thickness of the wall of the deep-brain abscesses were greater than those of superficial-brain abscesses and there was a positive correlation between the number of macrophages and the thickness of the abscess wall. The overall survival (OS) of patients with deep-brain abscess was not significantly shorter than that of patients with superficial-brain abscess. Furthermore, OS was not significantly different among groups of patients receiving different types of treatment. In conclusion, the wall of deep-brain abscesses is thicker than that of superficial abscesses and the infiltration of macrophages is abundant. The thick wall of abscesses in the deep brain may be associated with macrophage infiltration.

The prevalence of the iutA and ibeA genes in Escherichia coli isolates from severe and non-severe patients with bacteremic acute biliary tract infection is significantly different

Background

Although Escherichia coli is the most frequently isolated microorganism in acute biliary tract infections with bacteremia, data regarding its virulence are limited.

Results

Information on cases of bacteremia in acute biliary tract infection in a retrospective study was collected from 2013 to 2015 at a tertiary care hospital in Japan. Factors related to the severity of infection were investigated, including patient background, phylogenetic typing, and virulence factors of E. coli, such as adhesion, invasion, toxins, and iron acquisition.

In total, 72 E. coli strains were identified in 71 cases, most of which primarily belonged to the B2 phylogroup (68.1%). The presence of the iutA gene (77.3% in the non-severe group, 46.4% in the severe group, P = 0.011) and the ibeA gene (9.1% in the non-severe group, and 35.7% in the severe group, P = 0.012) was significantly associated with the severity of infection. Among the patient characteristics, diabetes mellitus with organ involvement and alkaline phosphatase were different in the severe and non-severe groups.

Conclusions

We showed that bacteremic E. coli strains from acute biliary tract infections belonged to the virulent (B2) phylogroup. The prevalence of the iutA and ibeA genes between the two groups of bacteremia severity was significantly different.

Role of fliC on biofilm formation, adhesion, and cell motility in Cronobacter malonaticus and regulation of luxS

Cronobacter malonaticus is one of the important foodborne pathogens causing infections mainly in adults. Biofilm formation, adhesion, and motility in Cronobacter have been documented, but the implying molecular mechanism has received little attention. Here, a comparison in biofilm formation, adhesion ability, and cell motility among wild type (WT), △luxS, and △fliC strains were analyzed using scanning electron microscope (SEM) and confocal laser scanning microscopy (CLSM). The thickest biofilm was formed by WT, followed by △luxS and △fliC. Furthermore, the deletion of fliC caused the loss of cell motility and the failure to flagella biosynthesis and mature biofilm formation. Besides, the adhesion abilities of △luxS and △fliC to biotic cells (LoVo and IEC-6) and abiotic surface (glass) were significantly decreased compared to WT, revealing that fliC might have an important role in the organism's invasion properties. We further demonstrated that the expression of negative regulator (flgM) of flagellin in △luxS was higher than that in WT, which indicated that luxS indirectly contributed to fliC expression. Our findings provided a novel perspective for precaution and control of C. malonaticus through intercepting fliC-mediated adhesion to biotic cells and abiotic surface.

Pathogenicity Factors of Genomic Islands in Intestinal and Extraintestinal Escherichia coli

Escherichia coli is a versatile bacterial species that includes both harmless commensal strains and pathogenic strains found in the gastrointestinal tract in humans and warm-blooded animals. The growing amount of DNA sequence information generated in the era of "genomics" has helped to increase our understanding of the factors and mechanisms involved in the diversification of this bacterial species. The pathogenic side of E. coli that is afforded through horizontal transfers of genes encoding virulence factors enables this bacterium to become a highly diverse and adapted pathogen that is responsible for intestinal or extraintestinal diseases in humans and animals. Many of the accessory genes acquired by horizontal transfers form syntenic blocks and are recognized as genomic islands (GIs). These genomic regions contribute to the rapid evolution, diversification and adaptation of E. coli variants because they are frequently subject to rearrangements, excision and transfer, as well as to further acquisition of additional DNA. Here, we review a subgroup of GIs from E. coli termed pathogenicity islands (PAIs), a concept defined in the late 1980s by Jörg Hacker and colleagues in Werner Goebel's group at the University of Würzburg, Würzburg, Germany. As with other GIs, the PAIs comprise large genomic regions that differ from the rest of the genome by their G + C content, by their typical insertion within transfer RNA genes, and by their harboring of direct repeats (at their ends), integrase determinants, or other mobility loci. The hallmark of PAIs is their contribution to the emergence of virulent bacteria and to the development of intestinal and extraintestinal diseases. This review summarizes the current knowledge on the structure and functional features of PAIs, on PAI-encoded E. coli pathogenicity factors and on the role of PAIs in host-pathogen interactions.

Memantine Displays Antimicrobial Activity by Enhancing Escherichia coli Pathogen-Induced Formation of Neutrophil Extracellular Traps

Bacterial infection remains one of the leading causes of death worldwide due to the continuous rise of multiple antibiotic-resistant bacteria. Focusing solely on bacteria as the drug targets is a major limitation inherent in the conventional antibiotic therapy. Recently, host-directed therapies have become such an innovative approach to modulate the host defense system and the interplay of innate and adaptive immunity. Our previous studies showed that memantine (MEM), an α7 nAChR antagonist, could efficiently block multi-drug resistant Escherichia coli-caused bacteremia and meningitis in a mouse model. However, the underlying mechanisms that govern the antibacterial effects of MEM are still unknown. In this study, we demonstrated that MEM is able to significantly suppress E. coli infection by enhancing E. coli-induced formation and release of NETs in vitro and in vivo. MEM could promote the trapping and bactericidal activities of the polymorphonuclear neutrophils (PMNs) in a manner dependent on α7 nAChR, since knockdown of this receptor noticeably reduces the survival ability of bacteria in PMNs while MEM no longer affects the survival of bacteria in PMNs. Our results also showed that when the expression of S100A9, an antiseptic protein, is inhibited, pathogen survival rates in PMNs increase significantly. MEM reverses this effect in a concentration-dependent manner. MEM stimulates the production of MPO, S100A9, and DNA in PMNs and accelerates the release of depolymerized chromatin fibers into the extracellular space, suggesting the formation of NETs. Taken together, our data suggest that MEM effectively blocks bacterial infection through the promotion of the antibacterial function of NETs induced by E. coli.

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.

Virulence Factors of Meningitis-Causing Bacteria: Enabling Brain Entry across the Blood-Brain Barrier

Infections of the central nervous system (CNS) are still a major cause of morbidity and mortality worldwide. Traversal of the barriers protecting the brain by pathogens is a prerequisite for the development of meningitis. Bacteria have developed a variety of different strategies to cross these barriers and reach the CNS. To this end, they use a variety of different virulence factors that enable them to attach to and traverse these barriers. These virulence factors mediate adhesion to and invasion into host cells, intracellular survival, induction of host cell signaling and inflammatory response, and affect barrier function. While some of these mechanisms differ, others are shared by multiple pathogens. Further understanding of these processes, with special emphasis on the difference between the blood-brain barrier and the blood-cerebrospinal fluid barrier, as well as virulence factors used by the pathogens, is still needed.

Virulence factor-dependent basolateral invasion of choroid plexus epithelial cells by pathogenic Escherichia coli in vitro

Escherichia coli is the most common Gram-negative causative agent of neonatal meningitis and E. coli meningitis is associated with high morbidity and mortality. Previous research has been carried out with regard to the blood-brain barrier and thereby unveiled an assortment of virulence factors involved in E. coli meningitis. Little, however, is known about the role of the blood-cerebrospinal fluid (CSF) barrier (BCSFB), in spite of several studies suggesting that the choroid plexus (CP) is a possible entry point for E. coli into the CSF spaces. Here, we used a human CP papilloma (HIBCPP) cell line that was previously established as valid model for the study of the BCSFB. We show that E. coli invades HIBCPP cells in a polar fashion preferentially from the physiologically relevant basolateral side. Moreover, we demonstrate that deletion of outer membrane protein A, ibeA or neuDB genes results in decreased cell infection, while absence of fimH enhances invasion, although causing reduced adhesion to the apical side of HIBCPP cells. Our findings suggest that the BCSFB might constitute an entry point for E. coli into the central nervous system, and HIBCPP cells are a valuable tool for investigating E. coli entry of the BCSFB.

High frequency of hybrid Escherichia coli strains with combined Intestinal Pathogenic Escherichia coli (IPEC) and Extraintestinal Pathogenic Escherichia coli (ExPEC) virulence factors isolated from human faecal samples

BACKGROUND

Classification of pathogenic Escherichia coli (E. coli) has traditionally relied on detecting specific virulence associated genes (VAGs) or combinations thereof. For E. coli isolated from faecal samples, the presence of specific genes associated with different intestinal pathogenic pathovars will determine their classification and further course of action. However, the E. coli genome is not a static entity, and hybrid strains are emerging that cross the pathovar definitions. Hybrid strains may show gene contents previously associated with several distinct pathovars making the correct diagnostic classification difficult. We extended the analysis of routinely submitted faecal isolates to include known virulence associated genes that are usually not examined in faecal isolates to detect the frequency of possible hybrid strains.

METHODS

From September 2012 to February 2013, 168 faecal isolates of E. coli routinely submitted to the Norwegian Institute of Public Health (NIPH) from clinical microbiological laboratories throughout Norway were analysed for 33 VAGs using multiplex-PCR, including factors associated with extraintestinal pathogenic E. coli (ExPEC) strains. The strains were further typed by Multiple Locus Variable-Number Tandem-Repeat Analysis (MLVA), and the phylogenetic grouping was determined. One isolate from the study was selected for whole genome sequencing (WGS) with a combination of Oxford Nanopore's MinION and Illumina's MiSeq.

RESULTS

The analysis showed a surprisingly high number of strains carrying ExPEC associated VAGs and strains carrying a combination of both intestinal pathogenic E. coli (IPEC) and ExPEC VAGs. In particular, 93.5% (101/108) of isolates classified as belonging to an IPEC pathovar additionally carried ExPEC VAGs. WGS analysis of a selected hybrid strain revealed that it could, with present classification criteria, be classified as belonging to all of the Enteropathogenic Escherichia coli (EPEC), Uropathogenic Escherichia coli (UPEC), Neonatal meningitis Escherichia coli (NMEC) and Avian pathogenic Escherichia coli (APEC) pathovars.

CONCLUSION

Hybrid ExPEC/IPEC E. coli strains were found at a very high frequency in faecal samples and were in fact the predominant species present. A sequenced hybrid isolate was confirmed to be a cross-pathovar strain possessing recognised hallmarks of several pathovars, and a genome heavily influenced by horizontal gene transfer.

Caspr1 is a host receptor for meningitis-causing Escherichia coli

Escherichia coli is the leading cause of neonatal Gram-negative bacterial meningitis, but the pathogenesis of E. coli meningitis remains elusive. E. coli penetration of the blood–brain barrier (BBB) is the critical step for development of meningitis. Here, we identify Caspr1, a single-pass transmembrane protein, as a host receptor for E. coli virulence factor IbeA to facilitate BBB penetration. Genetic ablation of endothelial Caspr1 and blocking IbeA–Caspr1 interaction effectively prevent E. coli penetration into the brain during meningitis in rodents. IbeA interacts with extracellular domain of Caspr1 to activate focal adhesion kinase signaling causing E. coli internalization into the brain endothelial cells of BBB. E. coli can invade hippocampal neurons causing apoptosis dependent on IbeA–Caspr1 interaction. Our results indicate that E. coli exploits Caspr1 as a host receptor for penetration of BBB resulting in meningitis, and that Caspr1 might be a useful target for prevention or therapy of E. coli meningitis.

Penetration of the blood–brain barrier (BBB) is crucial for development of E. coli-caused meningitis. Here, the authors show that a host membrane protein, Caspr1, acts as a receptor for a bacterial virulence factor to facilitate BBB penetration and entry of E. coli into brain neurons.

The serine/threonine protein kinase of Streptococcus suis serotype 2 affects the ability of the pathogen to penetrate the blood-brain barrier

Streptococcus suis serotype 2 (SS2) is a zoonotic agent that causes meningitis in humans and pigs. However, the mechanism whereby SS2 crosses the microvasculature endothelium of the brain is not understood. In this study, transposon (TnYLB-1) mutagenesis was used to identify virulence factors potentially associated with invasive ability in pathogenic SS2. A poorly invasive mutant was identified and was found to contain a TnYLB-1 insertion in the serine/threonine kinase (stk) gene. Transwell chambers containing hBMECs were used to model the blood-brain barrier (BBB). We observed that the SS2 wild-type ZY05719 strain crossed the BBB model more readily than the mutant strain. Hence, we speculated that STK is associated with the ability of crossing blood-brain barrier in SS2. In vitro, compared with ZY05719, the ability of the stk-deficient strain (Δstk) to adhere to and invade both hBMECs and bEnd.3 cells, as well as to cross the BBB, was significantly attenuated. Immunocytochemistry using antibodies against claudin-5 in bEnd.3 cells showed that infection by ZY05719 disrupted BBB tight junction proteins to a greater extent than in infection by Δstk. The studies revealed that SS2 initially binds at or near intercellular junctions and crosses the BBB via paracellular traversal. Claudin-5 mRNA levels were indistinguishable in ZY05719- and Δstk-infected cells. This result indicated that the decrease of claudin-5 was maybe induced by protein degradation. Cells infected by ZY05719 exhibited higher ubiquitination levels than cells infected by Δstk. This result indicated that ubiquitination was involved in the degradation of claudin-5. Differential proteomic analysis showed that E3 ubiquitin protein ligase HECTD1 decreased by 1.5-fold in Δstk-infected bEnd.3 cells relative to ZY05719-infected cells. Together, the results suggested that STK may affect the expression of E3 ubiquitin ligase HECTD1 and subsequently increase the degradation of claudin-5, thus enabling SS2 to traverse the BBB.

Molecular Epidemiology of Extraintestinal Pathogenic Escherichia coli

Extraintestinal pathogenic Escherichia coli (ExPEC) are important pathogens in humans and certain animals. Molecular epidemiological analyses of ExPEC are based on structured observations of E. coli strains as they occur in the wild. By assessing real-world phenomena as they occur in authentic contexts and hosts, they provide an important complement to experimental assessment. Fundamental to the success of molecular epidemiological studies are the careful selection of subjects and the use of appropriate typing methods and statistical analysis. To date, molecular epidemiological studies have yielded numerous important insights into putative virulence factors, host-pathogen relationships, phylogenetic background, reservoirs, antimicrobial-resistant strains, clinical diagnostics, and transmission pathways of ExPEC, and have delineated areas in which further study is needed. The rapid pace of discovery of new putative virulence factors and the increasing awareness of the importance of virulence factor regulation, expression, and molecular variation should stimulate many future molecular epidemiological investigations. The growing sophistication and availability of molecular typing methodologies, and of the new computational and statistical approaches that are being developed to address the huge amounts of data that whole genome sequencing generates, provide improved tools for such studies and allow new questions to be addressed.

The complete genome sequence of Cronobacter sakazakii ATCC 29544T, a food-borne pathogen, isolated from a child's throat

Background

Cronobacter sakazakii is an emerging opportunistic pathogen that is associated with rare but life-threatening cases of severe diseases: meningitis, necrotizing enterocolitis, and sepsis in premature and full-term infants. However, the pathogenesis mechanism of this pathogen remains largely unknown. To determine its pathogenesis at the genomic level, the genome of C. sakazakii ATCC 29544^T was completely sequenced and analyzed.

Results

The genomic DNA, containing a circular chromosome and three plasmids, is composed of 4,511,265 bp with a GC content of 56.71%, containing 4380 predicted open reading frames (ORFs), 22 rRNA genes, and 83 tRNA genes. The plasmids, designated pCSK29544_p1, pCSK29544_p2, and pCSK29544_p3, were 93,905-bp, 4938-bp, and 53,457-bp with GC contents of 57.02, 54.88, and 50.07%, respectively. They were also predicted to have 72, 6, and 57 ORFs without RNA genes.

Conclusions

The strain ATCC 29544^T genome has ompA and ibeB-homologous cusC genes, probably associated with the invasion of human brain microvascular endothelial cells (BMECs). In addition, gene clusters for siderophore production (iucABCD/iutA) and the related transport system (eitCBAD) were detected in pCSK29544_p1 plasmid, indicating better iron uptake ability for survival. Furthermore, to survive under extremely dry condition like milk powder, this genome has gene clusters for biosynthesis of capsular proteins (CSK29544_00281-00284) and cellulose (CSK29544_01124-01127) for biofilm formation and a gene cluster for utilization of sialic acid in the milk (nanKTAR). The genome information of C. sakazakii ATCC 29544^T would provide further understanding of its pathogenesis at the molecular level for the regulation of pathogenicity and the development of a rapid detection method using biomarkers.

Electronic supplementary material

The online version of this article (doi:10.1186/s13099-016-0150-0) contains supplementary material, which is available to authorized users.

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.

Chromosomal rearrangements and protein globularity changes in Mycobacterium tuberculosis isolates from cerebrospinal fluid

Background

Meningitis is a major cause of mortality in tuberculosis (TB). It is not clear what factors promote central nervous system invasion and pathology but it has been reported that certain strains of Mycobacterium tuberculosis (Mtb) might have genetic traits associated with neurotropism.

Methods

In this study, we generated whole genome sequences of eight clinical strains of Mtb that were isolated from the cerebrospinal fluid (CSF) of patients presenting with tuberculous meningitis (TBM) in Malaysia, and compared them to the genomes of H37Rv and other respiratory Mtb genomes either downloaded from public databases or extracted from local sputum isolates. We aimed to find genomic features that might be distinctly different between CSF-derived and respiratory Mtb.

Results

Genome-wide comparisons revealed rearrangements (translocations, inversions, insertions and deletions) and non-synonymous SNPs in our CSF-derived strains that were not observed in the respiratory Mtb genomes used for comparison. These rearranged segments were rich in genes for PE (proline-glutamate)/PPE (proline-proline-glutamate), transcriptional and membrane proteins. Similarly, most of the ns SNPs common in CSF strains were noted in genes encoding PE/PPE proteins. Protein globularity differences were observed among mycobacteria from CSF and respiratory sources and in proteins previously reported to be associated with TB meningitis. Transcription factors and other transcription regulators featured prominently in these proteins. Homologs of proteins associated with Streptococcus pneumoniae meningitis and Neisseria meningitidis virulence were identified in neuropathogenic as well as respiratory mycobacterial spp. examined in this study.

Discussion

The occurrence of in silico genetic differences in CSF-derived but not respiratory Mtb suggests their possible involvement in the pathogenesis of TBM. However, overall findings in this comparative analysis support the postulation that TB meningeal infection is more likely to be related to the expression of multiple virulence factors on interaction with host defences than to CNS tropism associated with specific genetic traits.

CD44-mediated monocyte transmigration across Cryptococcus neoformans-infected brain microvascular endothelial cells is enhanced by HIV-1 gp41-I90 ectodomain

Background

Cryptococcus neoformans (Cn) is an important opportunistic pathogen in the immunocompromised people, including AIDS patients, which leads to fatal cryptococcal meningitis with high mortality rate. Previous researches have shown that HIV-1 gp41-I90 ectodomain can enhance Cn adhesion to and invasion of brain microvascular endothelial cell (BMEC), which constitutes the blood brain barrier (BBB). However, little is known about the role of HIV-1 gp41-I90 in the monocyte transmigration across Cn-infected BBB. In the present study, we provide evidence that HIV-1 gp41-I90 and Cn synergistically enhance monocytes transmigration across the BBB in vitro and in vivo. The underlying mechanisms for this phenomenon require further study.

Methods

In this study, the enhancing role of HIV-1 gp41-I90 in monocyte transmigration across Cn-infected BBB was demonstrated by performed transmigration assays in vitro and in vivo.

Results

Our results showed that the transmigration rate of monocytes are positively associated with Cn and/or HIV-1 gp41-I90, the co-exposure (HIV-1 gp41-I90 + Cn) group showed a higher THP-1 transmigration rate (P < 0.01). Using CD44 knock-down HBMEC or CD44 inhibitor Bikunin in the assay, the facilitation of transmigration rates of monocyte enhanced by HIV-1 gp41-I90 was significantly suppressed. Western blotting analysis and biotin/avidin enzyme-linked immunosorbent assays (BA-ELISAs) showed that Cn and HIV-1 gp41-I90 could increase the expression of CD44 and ICAM-1 on the HBMEC. Moreover, Cn and/or HIV-1 gp41-I90 could also induce CD44 redistribution to the membrane lipid rafts. By establishing the mouse cryptococcal meningitis model, we found that HIV-1 gp41-I90 and Cn could synergistically enhance the monocytes transmigration, increase the BBB permeability and injury in vivo.

Conclusions

Collectively, our findings suggested that HIV-1 gp41-I90 ectodomain can enhance the transmigration of THP-1 through Cn-infected BBB, which may be mediated by CD44. This novel study enlightens the future prospects to elaborate the inflammatory responses induced by HIV-1 gp41-I90 ectodomain and to effectively eliminate the opportunistic infections in AIDS patients.

Pathogenic Triad in Bacterial Meningitis: Pathogen Invasion, NF-κB Activation, and Leukocyte Transmigration that Occur at the Blood-Brain Barrier

Bacterial meningitis remains the leading cause of disabilities worldwide. This life-threatening disease has a high mortality rate despite the availability of antibiotics and improved critical care. The interactions between bacterial surface components and host defense systems that initiate bacterial meningitis have been studied in molecular and cellular detail over the past several decades. Bacterial meningitis commonly exhibits triad hallmark features (THFs): pathogen penetration, nuclear factor-kappaB (NF-κB) activation in coordination with type 1 interferon (IFN) signaling and leukocyte transmigration that occur at the blood-brain barrier (BBB), which consists mainly of brain microvascular endothelial cells (BMEC). This review outlines the progression of these early inter-correlated events contributing to the central nervous system (CNS) inflammation and injury during the pathogenesis of bacterial meningitis. A better understanding of these issues is not only imperative to elucidating the pathogenic mechanism of bacterial meningitis, but may also provide the in-depth insight into the development of novel therapeutic interventions against this disease.

Molecular Epidemiology of Extraintestinal Pathogenic Escherichia coli

Extraintestinal pathogenic Escherichia coli (ExPEC), the specialized E. coli strains that possess the ability to overcome or subvert host defenses and cause extraintestinal disease, are important pathogens in humans and certain animals. Molecular epidemiological analysis has led to an appreciation of ExPEC as being distinct from other E. coli (including intestinal pathogenic and commensal variants) and has offered insights into the ecology, evolution, reservoirs, transmission pathways, host-pathogen interactions, and pathogenetic mechanisms of ExPEC. Molecular epidemiological analysis also provides an essential complement to experimental assessment of virulence mechanisms. This chapter first reviews the basic conceptual and methodological underpinnings of the molecular epidemiological approach and then summarizes the main aspects of ExPEC that have been investigated using this approach.

Virulence Gene Regulation in Escherichia coli

Escherichia colicauses three types of illnesses in humans: diarrhea, urinary tract infections, and meningitis in newborns. The acquisition of virulence-associated genes and the ability to properly regulate these, often horizontally transferred, loci distinguishes pathogens from the normally harmless commensal E. coli found within the human intestine. This review addresses our current understanding of virulence gene regulation in several important diarrhea-causing pathotypes, including enteropathogenic, enterohemorrhagic,enterotoxigenic, and enteroaggregativeE. coli-EPEC, EHEC, ETEC and EAEC, respectively. The intensely studied regulatory circuitry controlling virulence of uropathogenicE. coli, or UPEC, is also reviewed, as is that of MNEC, a common cause of meningitis in neonates. Specific topics covered include the regulation of initial attachment events necessary for infection, environmental cues affecting virulence gene expression, control of attaching and effacing lesionformation, and control of effector molecule expression and secretion via the type III secretion systems by EPEC and EHEC. How phage control virulence and the expression of the Stx toxins of EHEC, phase variation, quorum sensing, and posttranscriptional regulation of virulence determinants are also addressed. A number of important virulence regulators are described, including the AraC-like molecules PerA of EPEC, CfaR and Rns of ETEC, and AggR of EAEC;the Ler protein of EPEC and EHEC;RfaH of UPEC;and the H-NS molecule that acts to silence gene expression. The regulatory circuitry controlling virulence of these greatly varied E. colipathotypes is complex, but common themes offerinsight into the signals and regulators necessary forE. coli disease progression.

How Cryptococcus interacts with the blood-brain barrier

Cryptococcus demonstrates predilection for invasion of the brain, but the mechanism by which Cryptococcus crosses the blood-brain barrier (BBB) to cause brain invasion is largely unknown. In order for Cryptococcus to cross the BBB, there must be a way to either cross human brain microvascular endothelial cells, which are the main constitute of the BBB, or go in between tight junctions. Recent evidence of human brain microvascular endothelial cell responses to transcellular brain invasions includes membrane rearrangements, intracellular signaling pathways and cytoskeletal activations. Several Cryptococcal genes related to the traversal of BBB have been identified, including CPS1, ITR1a, ITR3c, PLB1, MPR1, FNX1 and RUB1. In addition, Cryptococcus neoformans-derived microvesicles may contribute to cryptococcal brain invasion. Paracellularly, Cryptococcus may traverse across BBB using either routes utilizing plasmin, ammonia or macrophages in a Trojan horse mechanism.

Insight into neonatal septicaemic Escherichia coli from India with respect to phylogroups, serotypes, virulence, extended-spectrum-β-lactamases and association of ST131 clonal group

The study characterizes a collection of 67 neonatal septicaemic Escherichia coli isolates on the basis of phylogroup, serotype, virulence, antibiotic resistance and also the association of CTX-M-producing E. coli and the ST131 clone in a developing country. Phylogroups B2 and D were predominant (33% and 19%, respectively). The most prevalent virulence factors (VFs) were traT (69%) and iucC (68%) and most VFs were concentrated in the B2 isolates. High levels of resistance (⩾70%) to cefotaxime, ciprofloxacin and trimethoprim/sulfamethoxazole was recorded but meropenem remained the most active antimicrobial. Six (9%) of the study isolates belonged to the ST131 clone, five of which were from the same hospital, and were either indistinguishable or closely related by pulsed-field gel electrophoresis. Although the prevalence of CTX-M-15-producing isolates was high (81%), the ST131 clone was relatively infrequent (11%) in extended spectrum β-lactamase (ESBL)-producers. The ST131 clone was characterized by the presence of bla CTX-M-15, qnrS, aac(6')-Ib-cr, IncF plasmids and virulence determinants such as iucC, papC, traT, usp, hlyA, iroN E.coli , cnf, and sat. We conclude that clonal spread of ST131 did not contribute directly to the high prevalence of CTX-M-15 in our settings.

IbeR facilitates stress-resistance, invasion and pathogenicity of avian pathogenic Escherichia coli

Systemic infections by avian pathogenic Escherichia coli (APEC) are economically devastating to poultry industries worldwide. IbeR, located on genomic island GimA, was shown to serve as an RpoS-like regulator in rpoS gene mutation neonatal meningitis E. coli (NMEC) RS218. However, the role of IbeR in pathogenicity of APEC carrying active RpoS has not yet been investigated. We showed that the APEC IbeR could elicit antibodies in infected ducks, suggesting that IbeR might be involved in APEC pathogenicity. To investigate the function of IbeR in APEC pathogenesis, mutant and complementation strains were constructed and characterized. Inactivation of ibeR led to attenuated virulence and reduced invasion capacity towards DF-1 cells, brains and cerebrospinal fluid (CSF) in vitro and in vivo. Bactericidal assays demonstrated that the mutant strain had impaired resistance to environmental stress and specific pathogen-free (SPF) chicken serum. These virulence-related phenotypes were restored by genetic complementation. Quantitative real-time reverse transcription PCR revealed that IbeR controlled expression of stress-resistance genes and virulence genes, which might led to the associated virulence phenotype.

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.

Composition of Escherichia coli population in the neonatal gut: phylogroups and virulence determinants

The composition of Escherichia coli in the neonatal gut has rarely been studied in developing countries. To gain insight into the composition of E. coli in the neonatal gut and to assess factors that could influence colonization by E. coli, analysis of the phylogenetic groups and virulence determinants of E. coli isolated from the guts of neonates in a tertiary care hospital was carried out. The distribution of the phylogroups of 124 E. coli isolates recovered showed that phylogroups A (23 %) and B1 (49 %) accounted for 72 % of the isolates. Isolates of the phylogenetic group B2 were rare (8 %). Virulence factors were also rare with the exception of aerobactin (iucC), which was detected in 45 % of the isolates and was significantly associated with phylogroup B1. Multinomial logistic regression established that colonization with phylogroup B1 was associated with a stay in the neonatal intensive care unit; phylogroup A was associated with a stay on the ward; and phylogroups B2 and D were associated with neonates delivered vaginally. Evaluation of the effect of different E. coli phylogroups, with and without identified virulence determinants, on the gut of neonatal mice showed histopathological changes in the mucosa. The severity of the changes could be correlated with the presence of virulence determinants, irrespective of the phylogroup.

Escherichia coli K1-induced cytopathogenicity of human brain microvascular endothelial cells

Pathophysiology of Escherichia coli sepsis is complex involving circulating bacterial products, cytokine release, and sustained bacteremia resulting in the damage of vascular endothelium. Here, it is shown that E. coli K1 produced cytopathogenicity of human brain microvascular endothelial cells (HBMEC), that constitute the blood-brain barrier. Whole bacteria or their conditioned medium produced severe HBMEC damage suggesting E. coli K1-cytopathogenicity is a contact-independent process. Using lipopolysaccharide (LPS) inhibitor, polymyxin B, purified LPS extracted from E. coli K1 as well as LPS mutant derived from E. coli K1, we showed that LPS is not the sole determinant of E. coli K1-mediated HBMEC death. Bacterial product(s) for HBMEC cytopathogenicity was heat-labile suggesting LPS-associated proteins. Several isogenic gene-deletion mutants (ΔompA, ΔibeA, ΔibeB, Δcnf1) exhibited HBMEC cytopathogenicity similar to that produced by wild type E. coli K1. E. coli K1-mediated HBMEC death was independent of phosphatidylinositol 3-kinase (PI3K) but dependent partially on focal adhesion kinase (FAK) using HBMEC expressing dominant negative FAK and PI3K.

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.

Escherichia coli isolates from extraintestinal organs of livestock animals harbour diverse virulence genes and belong to multiple genetic lineages

Escherichia coli, the most common cause of bacteraemia in humans in the UK, can also cause serious diseases in animals. However the population structure, virulence and antimicrobial resistance genes of those from extraintestinal organs of livestock animals are poorly characterised. The aims of this study were to investigate the diversity of these isolates from livestock animals and to understand if there was any correlation between the virulence and antimicrobial resistance genes and the genetic backbone of the bacteria and if these isolates were similar to those isolated from humans. Here 39 E. coli isolates from liver (n=31), spleen (n=5) and blood (n=3) of cattle (n=34), sheep (n=3), chicken (n=1) and pig (n=1) were assigned to 19 serogroups with O8 being the most common (n=7), followed by O101, O20 (both n=3) and O153 (n=2). They belong to 29 multi-locus sequence types, 20 clonal complexes with ST23 (n=7), ST10 (n=6), ST117 and ST155 (both n=3) being most common and were distributed among phylogenetic group A (n=16), B1 (n=12), B2 (n=2) and D (n=9). The pattern of a subset of putative virulence genes was different in almost all isolates. No correlation between serogroups, animal hosts, MLST types, virulence and antimicrobial resistance genes was identified. The distributions of clonal complexes and virulence genes were similar to other extraintestinal or commensal E. coli from humans and other animals, suggesting a zoonotic potential. The diverse and various combinations of virulence genes implied that the infections were caused by different mechanisms and infection control will be challenging.

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.

Cronobacter species (formerly known as Enterobacter sakazakii) in powdered infant formula: a review of our current understanding of the biology of this bacterium

Cronobacter species (formerly known as Enterobacter sakazakii) are opportunistic pathogens that can cause necrotizing enterocolitis, bacteraemia and meningitis, predominantly in neonates. Infection in these vulnerable infants has been linked to the consumption of contaminated powdered infant formula (PIF). Considerable research has been undertaken on this organism in the past number of years which has enhanced our understanding of this neonatal pathogen leading to improvements in its control within the PIF production environment. The taxonomy of the organism resulted in the recognition of a new genus, Cronobacter, which consists of seven species. This paper presents an up-to-date review of our current knowledge of Cronobacter species. Taxonomy, genome sequencing, current detection protocols and epidemiology are all discussed. In addition, consideration is given to the control of this organism in the manufacturing environment, as a first step towards reducing the occurrence of this pathogen in PIF.

Polyphosphate kinase 1 is required for the pathogenesis process of meningitic Escherichia coli K1 (RS218)

Aim: Polyphosphate kinase 1 (PPK1), encoded by the ppk1 gene, is one of the major enzymes to reversibly catalyze the synthesis of polyphosphate (poly P) from the terminal phosphate of ATP. Poly P confers resistance to stress in a number of bacterial species but its role in the virulence of meningitic bacterial pathogens is unknown. The aim of this study was to determine the role of PPK1 in the pathogenesis of Escherichia coli meningitis. Materials & methods: An isogenic in-frame ppk1 deletion mutant (PD44) of E. coli K1 strain E44 was constructed and characterized. Human brain microvascular endothelial cells and neonatal rats were used as the in vitro and in vivo models, respectively, to evaluate bacterial adhesion/invasion and the abilities of bacteria crossing the blood–brain barrier (BBB) to cause meningitis. The survival of PD44 and E44 under osmotic and acid stress conditions were also examined. Results: Poly P levels in E44 were clearly higher than those in PD44, especially at the stationary phase (SP). The ppk1 deletion mutant PD44 also showed poor survival rates during osmotic shock and acidic challenge, which the bacteria would face during pathogenesis. In vitro and in vivo assays revealed that PD44 was defective in bacterial adhesion and translocation across the BBB. By using the Evans blue method, we found that E44-induced permeability of the BBB in neonatal rats was significantly higher than that of the animals infected with PD44. Cytokine ELISA results showed that the TNF-α and IL-1β levels in the serum and brain tissues of the neonatal rats infected with PD44 were lower than that of the E44 group. A more obvious meningeal inflammation could be observed in the brain tissues of the rats infected with E44 when compared with that of the PD44 group by histopathological examination. Furthermore, the mRNA expression of IbeR, which is an RpoS-like regulator contributing to the SP regulation in E44, was found to be decreased in PD44 when compared with the parent strain. PD44 was also deficient in mRNA expression of the invasin IbeA, the adhesin FimH and the outer member protein A, which contributes to E44 penetration across BBB and resistance to the stimulations of low pH and high osmolarity. Conclusion: These results indicate that ppk1 plays an important role in stress adaption and virulence in meningitic E. coli K1 strain E44, and controls the relevant phenotypes by modulating the expression of the SP regulatory gene ibeR and the virulence genes ibeA, fimH and ompA.

Virulence of Escherichia coli clinical isolates in a murine sepsis model in relation to sequence type ST131 status, fluoroquinolone resistance, and virulence genotype

Escherichia coli sequence type ST131 (O25b:H4) has emerged over the past decade as a globally disseminated, multidrug-resistant pathogen. Unlike traditional antimicrobial-resistant E. coli, ST131 derives from virulence-associated phylogenetic group B2 and exhibits extraintestinal virulence factors. This, plus preliminary evidence of virulence in experimental animals, has suggested that ST131's epidemic emergence may be due to high virulence potential, compared with other E. coli types. To test this hypothesis, we compared a large number of matched ST131 and non-ST131 E. coli clinical isolates, both fluoroquinolone resistant and susceptible, plus isolates from classic extraintestinal pathogenic E. coli (ExPEC) sequence types (STs) and case report ST131 household transmission isolates, for virulence in a mouse subcutaneous sepsis model. Overall, in mice, the study isolates produced a wide range of lethality and clinical illness. However, neither ST131 status nor fluoroquinolone phenotype correlated with this diversity of illness severity, which occurred within each of the 6 study groups. In contrast, multiple known or suspected ExPEC virulence genes, including pap (P fimbriae), vat (vacuolating toxin), kpsM II (group 2 capsule), ibeA (invasion of brain endothelium), and clbB/N (colibactin synthesis), plus molecularly defined ExPEC status, were significantly associated with virulence. These findings point away from ST131 isolates as having higher virulence potential compared with other E. coli types in causing invasive extraintestinal infections and suggest instead that ST131's epidemiological success may reflect enhanced fitness for upstream steps in pathogenesis or in colonization and transmission. Additionally, the extensive within-ST virulence diversity suggests an opportunity to compare closely related strains to identify the responsible genetic determinants.

Comparative genomics of Escherichia coli strains causing urinary tract infections

The virulence determinants of uropathogenic Escherichia coli have been studied extensively over the years, but relatively little is known about what differentiates isolates causing various types of urinary tract infections. In this study, we compared the genomic profiles of 45 strains from a range of different clinical backgrounds, i.e., urosepsis, pyelonephritis, cystitis, and asymptomatic bacteriuria (ABU), using comparative genomic hybridization analysis. A microarray based on 31 complete E. coli sequences was used. It emerged that there is little correlation between the genotypes of the strains and their disease categories but strong correlation between the genotype and the phylogenetic group association. Also, very few genetic differences may exist between isolates causing symptomatic and asymptomatic infections. Only relatively few genes that could potentially differentiate between the individual disease categories were identified. Among these were two genomic islands, namely, pathogenicity island (PAI)-CFT073-serU and PAI-CFT073-pheU, which were significantly more associated with the pyelonephritis and urosepsis isolates than with the ABU and cystitis isolates. These two islands harbor genes encoding virulence factors, such as P fimbriae (pyelonephritis-associated fimbriae) and an important immunomodulatory protein, TcpC. It seems that both urovirulence and growth fitness can be attributed to an assortment of genes rather than to a specific gene set. Taken together, urovirulence and fitness are the results of the interplay of a mixture of factors taken from a rich menu of genes.

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.

The GimA locus of extraintestinal pathogenic E. coli: does reductive evolution correlate with habitat and pathotype?

IbeA (invasion of brain endothelium), which is located on a genomic island termed GimA, is involved in the pathogenesis of several extraintestinal pathogenic E. coli (ExPEC) pathotypes, including newborn meningitic E. coli (NMEC) and avian pathogenic E. coli (APEC). To unravel the phylogeny of GimA and to investigate its island character, the putative insertion locus of GimA was determined via Long Range PCR and DNA-DNA hybridization in 410 E. coli isolates, including APEC, NMEC, uropathogenic (UPEC), septicemia-associated E. coli (SEPEC), and human and animal fecal isolates as well as in 72 strains of the E. coli reference (ECOR) collection. In addition to a complete GimA (∼20.3 kb) and a locus lacking GimA we found a third pattern containing a 342 bp remnant of GimA in this strain collection. The presence of GimA was almost exclusively detected in strains belonging to phylogenetic group B2. In addition, the complete GimA was significantly more frequent in APEC and NMEC strains while the GimA remnant showed a higher association with UPEC strains. A detailed analysis of the ibeA sequences revealed the phylogeny of this gene to be consistent with that obtained by Multi Locus Sequence Typing of the strains. Although common criteria for genomic islands are partially fulfilled, GimA rather seems to be an ancestral part of phylogenetic group B2, and it would therefore be more appropriate to term this genomic region GimA locus instead of genomic island. The existence of two other patterns reflects a genomic rearrangement in a reductive evolution-like manner.

Identification of protective and broadly conserved vaccine antigens from the genome of extraintestinal pathogenic Escherichia coli

Extraintestinal pathogenic Escherichia coli (ExPEC) are a common cause of disease in both mammals and birds. A vaccine to prevent such infections would be desirable given the increasing antibiotic resistance of these bacteria. We have determined the genome sequence of ExPEC IHE3034 (ST95) isolated from a case of neonatal meningitis and compared this to available genome sequences of other ExPEC strains and a few nonpathogenic E. coli. We found 19 genomic islands present in the genome of IHE3034, which are absent in the nonpathogenic E. coli isolates. By using subtractive reverse vaccinology we identified 230 antigens present in ExPEC but absent (or present with low similarity) in nonpathogenic strains. Nine antigens were protective in a mouse challenge model. Some of them were also present in other pathogenic non-ExPEC strains, suggesting that a broadly protective E. coli vaccine may be possible. The gene encoding the most protective antigen was detected in most of the E. coli isolates, highly conserved in sequence and found to be exported by a type II secretion system which seems to be nonfunctional in nonpathogenic strains.