Strategy of Escherichia coli for crossing the blood-brain barrier

A live attenuated vaccine to prevent severe neonatal Escherichia coli K1 infections

Preterm birth is currently the leading cause of neonatal morbidity and mortality. Genetic, immunological and infectious causes are suspected. Preterm infants have a higher risk of severe bacterial neonatal infections, most of which are caused by Escherichia coli an in particular E. coli K1strains. Women with history of preterm delivery have a high risk of recurrence and therefore constitute a target population for the development of vaccine against E. coli neonatal infections. Here, we characterize the immunological, microbiological and protective properties of a live attenuated vaccine candidate in adult female mice and their pups against after a challenge by K1 and non-K1 strains of E. coli. Our results show that the E. coli K1 E11 ∆aroA vaccine induces strong immunity, driven by polyclonal bactericidal antibodies. In our model of meningitis, mothers immunized prior to mating transfer maternal antibodies to pups, which protect newborn mice against various K1 and non-K1 strains of E. coli. Given the very high mortality rate and the neurological sequalae associated with neonatal E. coli K1 meningitis, our results constitute preclinical proof of concept for the development of a live attenuated vaccine against severe E. coli infections in women at risk of preterm delivery.

Metabolomics and metagenomics reveal the impact of γδ T inhibition on gut microbiota and metabolism in periodontitis-promoting OSCC

During the process of periodontitis-promoting oral squamous cell carcinoma (OSCC), the periodontitis microbiota can facilitate OSCC development by activating γδ T cells. Inhibiting γδ T cells through immunotherapy has been shown to significantly alleviate various types of cancer. However, the underlying mechanism by which inhibiting γδ T cells influenced cancer treatment has not been fully elucidated. In this study, a mouse model of OSCC with periodontitis was established, and γδ T cells were inhibited by antibodies. Gut samples from the mice were collected and analyzed by metabolomics, metagenomics, and 16S rRNA. Integrative analysis of the gut metabolome and microbiome revealed that targeting γδ T resulted in changes in the levels of metabolites associated with cancer in the gut. Although there was no difference in the α diversity of microbiota, β diversity was significantly different, with a more heterogeneous community structure in the mice receiving targeted γδ T immunotherapy. Statistical analysis of the gut microbiota at the species level revealed a significant enrichment of Lactobacillus murinus, which was significantly correlated with γδ T abundance. The functional analysis revealed that inhibiting γδ T could impact the functional gene. A comprehensive analysis revealed that L. murinus is especially associated with changes in adenine, which also had connection with the concentration of IL-17 and the abundance of γδ T.IMPORTANCEThis study revealed the effect of γδ T cells on gut microbial dysbiosis and identify potential links between gut microbiota and metabolism, providing new insights into the role of γδ T during the process of periodontitis-induced OSCC, and identifying relevant biomarkers for future research and clinical monitoring protocol development.

The influence of physiological and pathological perturbations on blood-brain barrier function

The blood-brain barrier (BBB) is located at the interface between the vascular system and the brain parenchyma, and is responsible for communication with systemic circulation and peripheral tissues. During life, the BBB can be subjected to a wide range of perturbations or stresses that may be endogenous or exogenous, pathological or therapeutic, or intended or unintended. The risk factors for many diseases of the brain are multifactorial and involve perturbations that may occur simultaneously (e.g., two-hit model for Alzheimer's disease) and result in different outcomes. Therefore, it is important to understand the influence of individual perturbations on BBB function in isolation. Here we review the effects of eight perturbations: mechanical forces, temperature, electromagnetic radiation, hypoxia, endogenous factors, exogenous factors, chemical factors, and pathogens. While some perturbations may result in acute or chronic BBB disruption, many are also exploited for diagnostic or therapeutic purposes. The resultant outcome on BBB function depends on the dose (or magnitude) and duration of the perturbation. Homeostasis may be restored by self-repair, for example, via processes such as proliferation of affected cells or angiogenesis to create new vasculature. Transient or sustained BBB dysfunction may result in acute or pathological symptoms, for example, microhemorrhages or hypoperfusion. In more extreme cases, perturbations may lead to cytotoxicity and cell death, for example, through exposure to cytotoxic plaques.

World Health Organization critical priority Escherichia coli clone ST648 in magnificent frigatebird (Fregata magnificens) of an uninhabited insular environment

Antimicrobial resistance is an ancient natural phenomenon increasingly pressured by anthropogenic activities. Escherichia coli has been used as markers of environmental contamination and human-related activity. Seabirds may be bioindicators of clinically relevant bacterial pathogens and their antimicrobial resistance genes, including extended-spectrum-beta-lactamase (ESBL) and/or plasmid-encoded AmpC (pAmpC), in anthropized and remote areas. We evaluated cloacal swabs of 20 wild magnificent frigatebirds (Fregata magnificens) of the Alcatrazes Archipelago, the biggest breeding colony of magnificent frigatebirds in the southern Atlantic and a natural protected area with no history of human occupation, located in the anthropized southeastern Brazilian coast. We characterized a highly virulent multidrug-resistant ST648 (O153:H9) pandemic clone, harboring blaCTX–M–2, blaCMY–2, qnrB, tetB, sul1, sul2, aadA1, aac(3)-VIa and mdfA, and virulence genes characteristic of avian pathogenic (APEC) (hlyF, iroN, iss, iutA, and ompT) and other extraintestinal E. coli (ExPEC) (chuA, kpsMII, and papC). To our knowledge, this is the first report of ST648 E. coli co-producing ESBL and pAmpC in wild birds inhabiting insular environments. We suggest this potentially zoonotic and pathogenic lineage was likely acquired through indirect anthropogenic contamination of the marine environment, ingestion of contaminated seafood, or by intra and/or interspecific contact. Our findings reinforce the role of wild birds as anthropization sentinels in insular environments and the importance of wildlife surveillance studies on pathogens of critical priority classified by the World Health Organization.

Phosphopantetheinyl transferase ClbA contributes to the virulence of avian pathogenic Escherichia coli in meningitis infection of mice

Avian pathogenic Escherichia coli (APEC), which has potential zoonotic risk, can cause severe systemic infections such as septicemia and meningitis in poultry. Colibactin is a hybrid non-ribosomal peptide/polyketide secondary metabolite produced by bacteria, which induces double-strand DNA breaks and chromosome instability in eukaryotic cells. ClbA is a 4’-phosphopantetheinyl transferase (PPTase) that is essential for colibactin and plays a role in siderophore synthesis. However, whether ClbA is associated with meningitis development in APEC is unclear. In this study, we abolished the clbA gene in the APEC XM strain, investigated the effect of clbA on colibactin synthesis and evaluated the pathogenic capacity of colibactin on meningitis development. Deletion of clbA reduced DNA damage to cells and hindered the normal synthesis of colibactin. Compared with the mice infected by wild-type APEC XM, the clbA deletion mutant infected mice had significant reduction in a series of characteristics associated with meningitis including clinical symptoms, bacterial loads of blood and brain, disruption of the blood brain barrier and the expression of inflammatory factors in the brain tissue. Complementation of ClbA recovered some APEC XM virulence. We conclude that ClbA is obligatory for the synthesis of colibactin and is responsible for the development of meningitis in mice infected by APEC.

Colibactin in avian pathogenic Escherichia coli contributes to the development of meningitis in a mouse model

Colibactin is synthesized by a 54-kb genomic island, leads to toxicity in eukaryotic cells, and plays a vital role in many diseases, including neonatal sepsis and meningitis. Avian pathogenic Escherichia coli (APEC) is speculated to be an armory of extraintestinal pathogenic Escherichia coli and can be a potential zoonotic bacterium that threatens human and animal health. In this study, the APEC XM meningitis mouse model was successfully established to investigate the effect of colibactin in in vivo infection. The clbH-deletion mutant strain induced lower γ-H2AX expression, no megalocytosis, and no cell cycle arrest in bEnd.3 cells, which showed that the deletion of clbH decreased the production of colibactin in the APEC XM strain. The deletion of clbH did not affect the APEC XM strain’s ability of adhering to and invading bEnd.3 cells. In vitro, the non-colibactin-producing strain displayed significantly lower serum resistance and it also induced a lower level of cytokine mRNA and few disruptions of tight junction proteins in infected bEnd.3 cells. Meningitis did not occur in APEC ΔclbH-infected mice in vivo, who showed fewer clinical symptoms and fewer lesions on radiological and histopathological analyses. Compared with the APEX XM strain, APEC ΔclbH induced lower bacterial colonization in tissues, lower mRNA expression of cytokines in brain tissues, and slight destruction of the brain blood barrier. These results indicate that clbH is a necessary component for the synthesis of genotoxic colibactin, and colibactin is related to the development of meningitis induced by APEC XM.

The Perfect Condition for the Rising of Superbugs: Person-to-Person Contact and Antibiotic Use Are the Key Factors Responsible for the Positive Correlation between Antibiotic Resistance Gene Diversity and Virulence Gene Diversity in Human Metagenomes

Human metagenomes with a high diversity of virulence genes tend to have a high diversity of antibiotic-resistance genes and vice-versa. To understand this positive correlation, we simulated the transfer of these genes and bacterial pathogens in a community of interacting people that take antibiotics when infected by pathogens. Simulations show that people with higher diversity of virulence and resistance genes took antibiotics long ago, not recently. On the other extreme, we find people with low diversity of both gene types because they took antibiotics recently-while antibiotics select specific resistance genes, they also decrease gene diversity by eliminating bacteria. In general, the diversity of virulence and resistance genes becomes positively correlated whenever the transmission probability between people is higher than the probability of losing resistance genes. The positive correlation holds even under changes of several variables, such as the relative or total diversity of virulence and resistance genes, the contamination probability between individuals, the loss rate of resistance genes, or the social network type. Because the loss rate of resistance genes may be shallow, we conclude that the transmission between people and antibiotic usage are the leading causes for the positive correlation between virulence and antibiotic-resistance genes.

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.

Molecular and Phenotypic Characterization of Escherichia coli Associated with Granulomatous Colitis of Boxer Dogs

Invasive Escherichia coli is causally associated with granulomatous colitis (GC) of Boxer dogs and French Bulldogs. The virulence determinants of GC E. coli are unclear. E. coli isolated from 16 GC (36 strains) and 17 healthy control (HC: 33 strains) dogs were diverse in phylogeny, genotype, and serotype and lacked diarrheagenic genes. Genes encoding type II (gsp), IV (traC), and VI (hcp) secretion systems, long polar fimbriae (lpfA154/141), and iron acquisition (fyuA, chuA) were frequent in GC and HC. E. coli from 14/15 GC and 10/11 HC invaded Caco-2 better than non-pathogenic E. coli strain DH5α, with invasion correlated with motility and presence of chuA and colV. E. coli from all GC and 10/11 HC survived better than DH5α in J774 macrophages, with adherent-invasive E. coli (AIEC) in 60% GC and 73% HC. AIEC replicated in monocyte derived macrophages from a GC Boxer with CD48/SLAM risk haplotype but not the HC. Fluroquinolone resistant E. coli were less motile and invasive than fluoroquinolone sensitive (p < 0.05), and only 1/8 resistant strains met criteria for AIEC. In conclusion GC E. coli are diverse, resemble extraintestinal pathogenic E. coli (ExPEC), including AIEC, and can replicate in GC-susceptible macrophages. They are likely resident pathosymbionts that can opportunistically persist within macrophages of a GC-susceptible dog.

Transcriptome profiling of avian pathogenic Escherichia coli and the mouse microvascular endothelial cell line bEnd.3 during interaction

Background

Avian pathogenic Escherichia coli (APEC), an important extraintestinal pathogenic E. coli, causes colibacillosis, an acute and mostly systemic disease involving multiple organ lesions such as meningitis. Meningitis-causing APEC can invade the host central nervous system by crossing the blood–brain barrier (BBB), which is a critical step in the development of meningitis. However, the bacteria-host interaction mechanism in this process remains unclear.

Methods

In this study, we examined E. coli and bEnd.3 cells transcriptomes during infection and mock infection to investigate the global transcriptional changes in both organisms using RNA sequencing approach.

Results

When APEC infected the bEnd.3 cells, several significant changes in the expression of genes related to cell junctional complexes, extracellular matrix degradation, actin cytoskeleton rearrangement, immune activation and the inflammatory response in bEnd.3 cells were observed as compared to the mock infection group. Thus, the immune activation of bEnd.3 cells indicated that APEC infection activated host defenses. Furthermore, APEC may exploit cell junction degradation to invade the BBB. In addition, amino acid metabolism and energy metabolism related genes were downregulated and the protein export pathway related genes were upregulated in APEC cultured with bEnd.3 cells, compared to that in control. Thus, APEC may encounter starvation and express virulence factors during incubation with bEnd.3 cells.

Conclusion

This study provides a comprehensive overview of transcriptomic changes that occur during APEC infection of bEnd.3 cells, and offers insights into the bacterial invasion strategies and the subsequent host defense mechanism.

Characterization of Non-O157 Escherichia coli from Cattle Faecal Samples in the North-West Province of South Africa

Escherichia coli are commensal bacteria in the gastrointestinal tract of mammals, but some strains have acquired Shiga-toxins and can cause enterohemorrhagic diarrhoea and kidney failure in humans. Shiga-toxigenic E. coli (STEC) strains such as E. coli O157:H7 and some non-O157 strains also contain other virulence traits, some of which contribute to their ability to form biofilms. This study characterized non-O157 E. coli from South African cattle faecal samples for their virulence potential, antimicrobial resistance (AMR), biofilm-forming ability, and genetic relatedness using culture-based methods, pulsed-field gel electrophoresis (PFGE), and whole genome sequencing (WGS). Of 80 isolates screened, 77.5% (62/80) possessed Shiga-toxins genes. Of 18 antimicrobials tested, phenotypic resistance was detected against seven antimicrobials. Resistance ranged from 1.3% (1/80) for ampicillin-sulbactam to 20% (16/80) for tetracycline. Antimicrobial resistance genes were infrequently detected except for tetA, which was found in 31.3% (25/80) and tetB detected in 11.3% (9/80) of isolates. Eight biofilm-forming associated genes were detected in STEC isolates (n = 62) and two non-STEC strains. Prevalence of biofilm genes ranged from 31.3% (20/64) for ehaA^β passenger to 100% for curli structural subunit (csgA) and curli regulators (csgA and crl). Of the 64 STEC and multi-drug resistant isolates, 70.3% (45/64) and 37.5% (24/64) formed strong biofilms on polystyrene at 22 and 37 °C, respectively. Of 59 isolates screened by PFGE, 37 showed unique patterns and the remaining isolates were grouped into five clusters with a ≥90% relatedness. In silico serotyping following WGS on a subset of 24 non-O157 STEC isolates predicted 20 serotypes comprising three novel serotypes, indicating their diversity as potential pathogens. These findings show that North West South African cattle harbour genetically diverse, virulent, antimicrobial-resistant and biofilm-forming non-O157 E. coli. Biofilm-forming ability may increase the likelihood of persistence of these pathogens in the environment and facilitate their dissemination, increasing the risk of cross contamination or establishment of infections in hosts.

Effect of O antigen ligase gene mutation on oxidative stress resistance and pathogenicity of NMEC strain RS218

Escherichia coli is one of the primary causes of bacterial sepsis and meningitis in newborns. E. coli RS218, a prototype strain of neonatal meningitis E. coli (NMEC), is often used in research on the pathogenesis of NMEC. Phagocytes are crucial sentinels of immunity, and their antibacterial ability is largely determined by the capability to produce large amounts of ROS. The capacity of bacteria to endure oxidative pressure affects their colonization in the host. Here, we systematically screened the genes that plays key roles in the tolerance of the model of E. coli RS218 to peroxygen environment using a Tn5 mutant library. As a result, a gene encoding O antigen polymerase (O antigen ligase) that contains the Wzy_C superfamily domain (herein designated as Ocw) was identified in E. coli RS218. Furthermore, we constructed an isogenic deletion mutant of ocw gene and its complementary strain in E. coli. Our results revealed that ocw affects the lipopolysaccharide synthesis, ROS tolerance, and survival of E. coli in the host environment. The discovery of ocw provides important clues for better understanding the function of O-antigen.

Antigenic epitopes on the outer membrane protein A of Escherichia coli identified with single-chain variable fragment (scFv) antibodies

Bacterial meningitis is a severe disease that is fatal to one-third of patients. The major cause of meningitis in neonates is Escherichia coli (E. coli) K1. This bacterium synthesizes an outer membrane protein A (OmpA) that is responsible for the adhesion to (and invasion of) endothelial cells. Thus, the OmpA protein represents a potential target for developing diagnostic and therapeutic agents for meningitis. In this study, we expressed recombinant OmpA proteins with various molecular weights in E. coli. The sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) was performed to check the molecular size of OmpA's full length (FL) and truncated proteins. OmpA-FL protein was purified for immunizing chickens to produce immunoglobulin yolk (IgY) antibodies. We applied phage display technology to construct antibody libraries (OmpA-FL scFv-S 1.1 × 10⁷ and OmpA-FL scFv-L 5.01 × 10⁶) to select specific anti-OmpA-FL scFv antibodies; these were characterized by their binding ability to recombinant or endogenous OmpA using ELISA, immunofluorescent staining, and confirmed with immunoblotting. We found 12 monoclonal antibodies that react to OmpA fragments; seven scFvs recognize fragments spanning amino acid (aa) residues 1-346, aa 1-287, aa 1-167, and aa 60-192, while five scFvs recognize fragments spanning aa 1-346 and aa 1-287 only. Two fragments (aa 246-346 and aa 287-346) were not recognized with any of the 12 scFvs. Together, the data suggest three antigenic epitopes (60 aa-160 aa, 161 aa-167 aa, 193 aa-245 aa) recognized by monoclonal antibodies. These scFv antibodies show strong reactivity against OmpA proteins. We believe that antibodies show promising diagnostic agents for E. coli K1 meningitis.

Transactivated Epidermal Growth Factor Receptor Recruitment of α-actinin-4 From F-actin Contributes to Invasion of Brain Microvascular Endothelial Cells by Meningitic Escherichia coli

Bacterial penetration of the blood-brain barrier requires its successful invasion of brain microvascular endothelial cells (BMECs), and host actin cytoskeleton rearrangement in these cells is a key prerequisite for this process. We have reported previously that meningitic Escherichia coli can induce the activation of host's epidermal growth factor receptor (EGFR) to facilitate its invasion of BMECs. However, it is unknown how EGFR specifically functions during this invasion process. Here, we identified an important EGFR-interacting protein, α-actinin-4 (ACTN4), which is involved in maintaining and regulating the actin cytoskeleton. We observed that transactivated-EGFR competitively recruited ACTN4 from intracellular F-actin fibers to disrupt the cytoskeleton, thus facilitating bacterial invasion of BMECs. Strikingly, this mechanism operated not only for meningitic E. coli, but also for infections with Streptococcus suis, a Gram-positive meningitis-causing bacterial pathogen, thus revealing a common mechanism hijacked by these meningitic pathogens where EGFR competitively recruits ACTN4. Ever rising levels of antibiotic-resistant bacteria and the emergence of their extended-spectrum antimicrobial-resistant counterparts remind us that EGFR could act as an alternative non-antibiotic target to better prevent and control bacterial meningitis.

High-Throughput Chip Assay for Investigating Escherichia coli Interaction with the Blood-Brain Barrier Using Microbial and Human Proteome Microarrays (Dual-Microarray Technology)

Bacterial meningitis in neonates and infants is an acute lethal disease and occurs in response to microbial exploitation of the blood-brain barrier (BBB), resulting in the intracranial inflammation. Several pathogens, such as Escherichia coli ( E. coli), can cause this devastating disease; however, the underlying molecular mechanisms by which these pathogens exploit the BBB remain incompletely understood. To identify important players on both the pathogen and host sides that govern the E. coli-BBB cell interactions, we took advantage of the E. coli and human proteome microarrays (i.e., HuProt) as an unbiased, proteome-wide tool for identification of important players on both sides. Using the E. coli proteome microarrays, we developed a unique high throughput chip-based cell probing assay to probe with fluorescent live human brain microvascular endothelial cells (HBMEC, which constitute the BBB). We identified several transmembrane proteins, which effectively bound to live HBMEC. We focused on YojI protein for further study. By probing the HuProt arrays with YojI, interferon-alpha receptor (IFNAR2) was identified as one of its binding proteins. The importance of YojI and IFNAR2 involved in E. coli-HBMEC interactions was characterized using the YojI knockout bacteria and IFNAR2-knock down HBMEC and further confirmed by E. coli binding assay in HBMEC. This study represents a new paradigm (dual-microarray technology) that enables rapid, unbiased discovery of both pathogen and host players that are involved in pathogen-host interactions for human infectious diseases in a high throughput manner.

Brucella abortus Traverses Brain Microvascular Endothelial Cells Using Infected Monocytes as a Trojan Horse

Neurobrucellosis is an inflammatory disease caused by the invasion of Brucella spp. to the central nervous system (CNS). The pathogenesis of the disease is not well characterized; however, for Brucella to gain access to the brain parenchyma, traversing of the blood-brain barrier (BBB) must take place. To understand the CNS determinants of the pathogenesis of B. abortus, we have used the in vitro BBB model of human brain microvascular endothelial cells (HBMEC) to study the interactions between B. abortus and brain endothelial cells. In this study, we showed that B. abortus is able to adhere and invade HBMEC which was dependent on microtubules, microfilaments, endosome acidification and de novo protein synthesis. After infection, B. abortus rapidly escapes the endosomal compartment of HBMEC and forms a replicative Brucella-containing vacuole that involves interactions with the endoplasmic reticulum. Despite the ability of B. abortus to invade and replicate in HBMEC, the bacterium was unable by itself to traverse HBMEC, but could traverse polarized HBMEC monolayers within infected monocytes. Importantly, infected monocytes that traversed the HBMEC monolayer were a bacterial source for de novo infection of glial cells. This is the first demonstration of the mechanism whereby B. abortus is able to traverse the BBB and infect cells of the CNS. These results may have important implications in our understanding of the pathogenesis of neurobrucellosis.

Activin A increases phagocytosis of Escherichia coli K1 by primary murine microglial cells activated by toll-like receptor agonists

Background

Bacterial meningitis is associated with high mortality and long-term neurological sequelae. Increasing the phagocytic activity of microglia could improve the resistance of the CNS against infections. We studied the influence of activin A, a member of the TGF-β family with known immunoregulatory and neuroprotective effects, on the functions of microglial cells in vitro.

Methods

Primary murine microglial cells were treated with activin A (0.13 ng/ml–13 μg/ml) alone or in combination with agonists of TLR2, 4, and 9. Phagocytosis of Escherichia coli K1 as well as release of TNF-α, IL-6, CXCL1, and NO was assessed.

Results

Activin A dose-dependently enhanced the phagocytosis of Escherichia coli K1 by microglial cells activated by agonists of TLR2, 4, and 9 without further increasing NO and proinflammatory cytokine release. Cell viability of microglial cells was not affected by activin A.

Conclusions

Priming of microglial cells with activin A could increase the elimination of bacteria in bacterial CNS infections. This preventive strategy could improve the resistance of the brain to infections, particularly in elderly and immunocompromised patients.

Screening of a Drug Library Identifies Inhibitors of Cell Intoxication by CNF1

Cytotoxic necrotizing factor 1 (CNF1) is a toxin produced by pathogenic strains of Escherichia coli responsible for extra-intestinal infections. CNF1 deamidates Rac1, thereby triggering its permanent activation and worsening inflammatory reactions. Activated Rac1 is prone to proteasomal degradation. There is no targeted therapy against CNF1, despite its clinical relevance. In this work we developed a fluorescent cell-based immunoassay to screen for inhibitors of CNF1-induced Rac1 degradation among 1120 mostly approved drugs. Eleven compounds were found to prevent CNF1-induced Rac1 degradation, and five also showed a protective effect against CNF1-induced multinucleation. Finally, lasalocid, monensin, bepridil, and amodiaquine protected cells from both diphtheria toxin and CNF1 challenges. These data highlight the potential for drug repurposing to fight several bacterial infections and Rac1-based diseases.

M60-like metalloprotease domain of the Escherichia coli YghJ protein forms amyloid fibrils

Amyloids are protein fibrils with a characteristic spatial structure. Amyloids were long perceived as the pathogens involved in a set of lethal diseases in humans and animals. In recent decades, it has become clear that amyloids represent a quaternary protein structure that is not only pathological but also functionally important and is widely used by different organisms, ranging from archaea to animals, to implement diverse biological functions. The greatest biological variety of amyloids is found in prokaryotes, where they control the formation of biofilms and cell wall sheaths, facilitate the overcoming of surface tension, and regulate the metabolism of toxins. Several amyloid proteins were identified in the important model, biotechnological and pathogenic bacterium Escherichia coli. In previous studies, using a method for the proteomic screening and identification of amyloids, we identified 61 potentially amyloidogenic proteins in the proteome of E. coli. Among these proteins, YghJ was the most enriched with bioinformatically predicted amyloidogenic regions. YghJ is a lipoprotein with a zinc metalloprotease M60-like domain that is involved in mucin degradation in the intestine as well as in proinflammatory responses. In this study, we analyzed the amyloid properties of the YghJ M60-like domain and demonstrated that it forms amyloid-like fibrils in vitro and in vivo.

Human Meningitis-Associated Escherichia coli

Escherichia coli is the most common Gram-negative bacillary organism causing meningitis, and E. coli meningitis continues to be an important cause of mortality and morbidity throughout the world. Our incomplete knowledge of its pathogenesis contributes to such mortality and morbidity. Recent reports of E. coli strains producing CTX-M-type or TEM-type extended-spectrum β-lactamases create a challenge. Studies using in vitro and in vivo models of the blood-brain barrier have shown that E. coli meningitis follows a high degree of bacteremia and invasion of the blood-brain barrier. E. coli invasion of the blood-brain barrier, the essential step in the development of E. coli meningitis, requires specific microbial and host factors as well as microbe- and host-specific signaling molecules. Blockade of such microbial and host factors contributing to E. coli invasion of the blood-brain barrier is shown to be efficient in preventing E. coli penetration into the brain. The basis for requiring a high degree of bacteremia for E. coli penetration of the blood-brain barrier, however, remains unclear. Continued investigation on the microbial and host factors contributing to a high degree of bacteremia and E. coli invasion of the blood-brain barrier is likely to identify new targets for prevention and therapy of E. coli meningitis.

Outer membrane protein A: An immunogenic protein induces highly protective efficacy against Vibrio ichthyoenteri

Vibrio ichthyoenteri was an important causative agent of bacterial enteritis in flounder (Paralichthys olivaceus). Outer membrane protein A (OmpA) of Gram-negative pathogen was a major cell surface antigen. In the present study, OmpA of V. ichthyoenteri was recombinantly expressed in Escherichia coli, and the immunogenicity of OmpA was identified by western blotting using flounder anti-rOmpA and anti-V. ichthyoenteri antibodies. The vaccine potential of rOmpA was tested in a flounder model, and a high relative percentage of survival rate was obtained with 73.1% after challenge with V. ichthyoenteri. Meanwhile, the immune response of flounder induced by rOmpA was also investigated, and the results showed that the sIg + lymphocytes in blood, spleen, and pronephros significantly proliferated, and the peak levels occurred at week 4 after immunization. Moreover, rOmpA could induce higher levels of specific serum antibodies than the control group after immunization, and the peak level occurred at week 5 after immunization. Meanwhile, qRT-PCR analysis showed that the expressions of CD4-1, CD8α, IL-1β, IFN-γ, MHCIα and MHCIIα genes were significantly up-regulated after immunization with rOmpA. Taking together, these results demonstrated that rOmpA could evoke highly protective effects against V. ichthyoenteri challenge and induce strong immune response of flounder, which indicated that OmpA was a promising vaccine candidate.

Pertussis Toxin Exploits Host Cell Signaling Pathways Induced by Meningitis-Causing E. coli K1-RS218 and Enhances Adherence of Monocytic THP-1 Cells to Human Cerebral Endothelial Cells

Pertussis toxin (PTx), the major virulence factor of the whooping cough-causing bacterial pathogen Bordetella pertussis, permeabilizes the blood–brain barrier (BBB) in vitro and in vivo. Breaking barriers might promote translocation of meningitis-causing bacteria across the BBB, thereby facilitating infection. PTx activates several host cell signaling pathways exploited by the neonatal meningitis-causing Escherichia coli K1-RS218 for invasion and translocation across the BBB. Here, we investigated whether PTx and E. coli K1-RS218 exert similar effects on MAPK p38, NF-κB activation and transcription of downstream targets in human cerebral endothelial TY10 cells using qRT-PCR, Western blotting, and ELISA in combination with specific inhibitors. PTx and E. coli K1-RS218 activate MAPK p38, but only E. coli K1-RS218 activates the NF-κB pathway. mRNA and protein levels of p38 and NF-κB downstream targets including IL-6, IL-8, CxCL-1, CxCL-2 and ICAM-1 were increased. The p38 specific inhibitor SB203590 blocked PTx-enhanced activity, whereas E. coli K1-RS218’s effects were inhibited by the NF-κB inhibitor Bay 11-7082. Further, we found that PTx enhances the adherence of human monocytic THP-1 cells to human cerebral endothelial TY10 cells, thereby contributing to enhanced translocation. These modulations of host cell signaling pathways by PTx and meningitis-causing E. coli support their contributions to pathogen and monocytic THP-1 cells translocation across the BBB.

SILAC and LC-MS/MS identification of Streptococcus equi ssp. zooepidemicus proteins that contribute to mouse brain microvascular endothelial cell infection

Streptococcus equi ssp. zooepidemicus (SEZ) causes meningitis in both humans and animals. Some dissociative proteins of SEZ are cytotoxic to mouse brain microvascular endothelial cells (mBMECs) and may contribute to the penetration of SEZ across the blood-brain barrier (BBB). In this study, the ability of SEZ to penetrate across an in vitro BBB model was confirmed. We used stable isotope labeling with amino acids in cell culture (SILAC) to label SEZ proteins with heavy or light isotope-tagged amino acids, along with LC-MS/MS to determine which SEZ proteins were involved in interactions with mBMECs. The efficiency of SEZ protein isotope labeling was 94.7 %, which was sufficient for further analysis. Forty-nine labeled peptides were identified as binding to mBMECs, which matched to 25 SEZ proteins. Bioinformatic analysis indicated that most of these proteins were cytoplasmic. These proteins may have functions in breaching the host BBB, and some of them are known virulence factors in other bacteria. Indirect immunofluorescence results indicated that SEZ enolase had binding activity toward mBMECs. Protective test results showed that enolase was a protective antigen against SEZ infection. This research is the first application of SILAC combined with LC-MS/MS to identify SEZ proteins that may contribute to the infection of mBMECs and potentially show functions related to breaching the BBB. The outcomes provide many future avenues for research into the mechanism of SEZ-induced meningitis.

Pertussis Toxin Exploits Specific Host Cell Signaling Pathways for Promoting Invasion and Translocation of Escherichia coli K1 RS218 in Human Brain-derived Microvascular Endothelial Cells

Pertussis toxin (PTx), an AB5 toxin and major virulence factor of the whooping cough-causing pathogen Bordetella pertussis, has been shown to affect the blood-brain barrier. Dysfunction of the blood-brain barrier may facilitate penetration of bacterial pathogens into the brain, such as Escherichia coli K1 (RS218). In this study, we investigated the influence of PTx on blood-brain barrier permissiveness to E. coli infection using human brain-derived endothelial HBMEC and TY10 cells as in vitro models. Our results indicate that PTx acts at several key points of host cell intracellular signaling pathways, which are also affected by E. coli K1 RS218 infection. Application of PTx increased the expression of the pathogen binding receptor gp96. Further, we found an activation of STAT3 and of the small GTPase Rac1, which have been described as being essential for bacterial invasion involving host cell actin cytoskeleton rearrangements at the bacterial entry site. In addition, we showed that PTx induces a remarkable relocation of VE-cadherin and β-catenin from intercellular junctions. The observed changes in host cell signaling molecules were accompanied by differences in intracellular calcium levels, which might act as a second messenger system for PTx. In summary, PTx not only facilitates invasion of E. coli K1 RS218 by activating essential signaling cascades; it also affects intercellular barriers to increase paracellular translocation.

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 choroid plexus-a multi-role player during infectious diseases of the CNS

The choroid plexus (CP) is the source of cerebrospinal fluid (CSF) production and location of the blood-CSF barrier (BCSFB), which is constituted by the epithelial cells of the CP. Several infectious pathogens including viruses, bacteria, fungi and parasites cross the BCSFB to enter the central nervous system (CNS), ultimately leading to inflammatory infectious diseases like meningitis and meningoencephalitis. The CP responds to this challenge by the production of chemokines and cytokines as well as alterations of the barrier function of the BCSFB. During the course of CNS infectious disease host immune cells enter the CNS, eventually contributing to the cellular damage caused by the disease. Additional complications, which are in certain cases caused by choroid plexitis, can arise due to the response of the CP to the pathogens. In this review we will give an overview on the multiple functions of the CP during brain infections highlighting the CP as a multi-role player during infectious diseases of the CNS. In this context the importance of tools for investigation of these CP functions and a possible suitability of the CP as therapeutic target will be discussed.

Vitamin D deficiency decreases survival of bacterial meningoencephalitis in mice

Background

Meningoencephalitis caused by Escherichia coli is associated with high rates of mortality and risk of neurological sequelae in newborns and infants and in older or immunocompromised adults. A high prevalence of neurological disorders has been observed in geriatric populations at risk of hypovitaminosis D.

Methods

In vivo, we studied the effects of vitamin D3 on survival and the host’s immune response in experimental bacterial meningoencephalitis in mice after intracerebral E. coli infection. To produce different systemic vitamin D3 concentrations, mice received a low, standard, or high dietary vitamin D3 supplementation. Bacterial titers in blood, spleen, and brain homogenates were determined. Leukocyte infiltration was assessed by histological scores, and tissue cytokine or chemokine concentrations were measured.

Results

Mice fed a diet with low vitamin D3 concentration died earlier than control animals after intracerebral infection. Vitamin D deficiency did not inhibit leukocyte recruitment into the subarachnoid space and did not lead to an increased density of bacteria in blood, spleen, or brain homogenates. The release of proinflammatory interleukin (IL)-6 was decreased and the release of anti-inflammatory IL-10 was increased in mice fed a diet with high vitamin D3 supplementation.

Conclusion

Our observations suggest a detrimental role of vitamin D deficiency in bacterial central nervous system infections. Vitamin D may exert immune regulatory functions.

Complete nucleotide sequence of pRS218, a large virulence plasmid, that augments pathogenic potential of meningitis-associated Escherichia coli strain RS218

BACKGROUND

Escherichia coli is the most predominant Gram-negative bacterial pathogen associated with neonatal meningitis. Previous studies indicated that the prototypic neonatal meningitis E. coli (NMEC) strain RS218 (O18:K1:H7) harbors one large plasmid. Objectives of the present study were to analyze the complete nucleotide sequence of this large plasmid (pRS218) and its contribution to NMEC pathogenesis using in vitro and in vivo models of neonatal meningitis.

RESULTS

The plasmid is 114,231 bp in size, belongs to the incompatibility group FIB/IIA (IncFIB/IIA), and contains a genetic load region that encodes several virulence and fitness traits such as enterotoxicity, iron acquisition and copper tolerance. The nucleotide sequence of pRS218 showed a 41- 46% similarity to other neonatal meningitis-causing E. coli (NMEC) plasmids and remarkable nucleotide sequence similarity (up to 100%) to large virulence plasmids of E. coli associated with acute cystitis. Some genes located on pRS218 were overly represented by NMEC strains compared to fecal E. coli isolated from healthy individuals. The plasmid-cured strain was significantly attenuated relative to the RS218 wild-type strain as determined in vitro by invasion potential to human cerebral microvascular endothelial cells and in vivo by mortalities, histopathological lesions in the brain tissue, and bacterial recovery from the cerebrospinal fluid of infected rat pups.

CONCLUSIONS

The pRS218 is an IncFIB/IIA plasmid which shares a remarkable nucleotide sequence similarity to large plasmids of E. coli associated with cystitis. Both in vitro and in vivo experiments indicated that pRS218 plays an important role in NMEC pathogenesis.

Zyxin modulates the transmigration of Haemophilus influenzae to the central nervous system

The mechanism by which Haemophilus influenzae causes meningitis is unclear. Previously, we established murine meningitis by intranasal instillation of H. influenzae as a cell-bound organism (CBO). In this study, we aimed to identify the molecules associated with inhibiting the transmigration of cells across the blood-brain barrier (BBB). Two-dimensional difference gel electrophoresis and protein identification by mass spectrometry were used for proteomic analysis. Analysis of the membranous extract from a tumor necrosis factor (TNF)-α-treated human brain microvascular endothelial cell (HBMEC) monolayer revealed 41 differentially expressed proteins. Zyxin, which is thought to be essential for tight cell-to-cell junctions, decreased 1.8-fold in TNF-α-treated HBMECs. In addition, zyxin transcript levels decreased 1.5-fold in cells derived from TNF-α-treated HBMECs. Intranasal instillation of CBOs in zyxin-deficient mice resulted in a significant higher mortality rate than in wild-type mice. Transmigration of CBOs across a HBMEC monolayer pretreated with TNF-α (1 ng/mL), interleukin (IL)-1β (10 ng/mL), or lipopolysaccharide (LPS; 10 ng/mL) was assayed by counting CBOs that migrated from an upper chamber into a lower chamber. HBMEC pretreated with TNF-α exhibited significantly greater migration (P<0.01) than did control cells or cells treated with IL-1β or LPS. Our findings highlight that zyxin is an important protein protecting the tight junction of the BBB against cell transmigration across the BBB. Finally, TNF-α produced in respiratory infection when the primary infection reached the BBB caused decreased zyxin levels in BBB cell membranes. Furthermore, H. influenzae reaching the BBB as CBOs could transmigrate into cerebrospinal fluid across the zyxin-decreased BBB.

Two functional type VI secretion systems in avian pathogenic Escherichia coli are involved in different pathogenic pathways

Type VI secretion systems (T6SSs) are involved in the pathogenicity of several Gram-negative bacteria. The VgrG protein, a core component and effector of T6SS, has been demonstrated to perform diverse functions. The N-terminal domain of VgrG protein is a homologue of tail fiber protein gp27 of phage T4, which performs a receptor binding function and determines the host specificity. Based on sequence analysis, we found that two putative T6SS loci exist in the genome of the avian pathogenic Escherichia coli (APEC) strain TW-XM. To assess the contribution of these two T6SSs to TW-XM pathogenesis, the crucial clpV clusters of these two T6SS loci and their vgrG genes were deleted to generate a series of mutants. Consequently, T6SS1-associated mutants presented diminished adherence to and invasion of several host cell lines cultured in vitro, decreased pathogenicity in duck and mouse infection models in vivo, and decreased biofilm formation and bacterial competitive advantage. In contrast, T6SS2-associated mutants presented a significant decrease only in the adherence to and invasion of mouse brain microvascular endothelial cell (BMEC) line bEnd.3 and brain tissue of the duck infection model. These results suggested that T6SS1 was involved in the proliferation of APEC in systemic infection, whereas VgrG-T6SS2 was responsible only for cerebral infection. Further study demonstrated that VgrG-T6SS2 was able to bind to the surface of bEnd.3 cells, whereas it did not bind to DF-1 (chicken embryo fibroblast) cells, which further proved the interaction of VgrG-T6SS2 with the surface of BMECs.

Fatal fungemia due to Paracoccidioides lutzii

We report the first case of fungemia caused by Paracoccidioides lutzii in a 51-year-old male farm worker from the central-west region of Brazil. The fungus was isolated from blood cultures and the species was confirmed by phylogenetic identification. Despite specific treatment and intensive care, the patient died 39 days after admission.

Intraperitoneal prophylaxis with CpG oligodeoxynucleotides protects neutropenic mice against intracerebral Escherichia coli K1 infection

Background

Prophylaxis with unmethylated cytosine phosphate guanidine (CpG) oligodeoxynucleotides (ODN) protects against several systemic experimental infections. Escherichia coli is a major cause of Gram-negative neonatal bacterial meningitis and also causes meningitis and meningoencephalitis in older and immunocompromised patients.

Methods

Wild-type (wt) and Toll-like receptor 9 (TLR9)-deficient mice were rendered neutropenic by intraperitoneal administration of the anti-Ly-6G monoclonal antibody. Immunocompetent and neutropenic mice received intraperitoneal CpG ODN or vehicle 72 h prior to induction of E. coli K1 meningoencephalitis.

Results

Pre-treatment with CpG ODN significantly increased survival of neutropenic wt mice from 33% to 75% (P = 0.0003) but did not protect neutropenic TLR9^-/- mice. The protective effect of CpG ODN was associated with an enhanced production of interleukin (IL)-12/IL-23p40 with sustained increased levels in serum and spleen at least for 17 days after conditioning compared to buffer-treated animals. CpG-treated neutropenic wt mice showed reduced bacterial concentrations and increased recruitment of Ly6C^highCCR2⁺ monocytes in brain and spleen 42 h after infection. The levels of macrophage inflammatory protein 1α (MIP-1α) and interferon gamma (IFN-γ) in spleen were higher 42 h after infection in CpG-treated compared to buffer-treated neutropenic animals. In immunocompetent mice, prophylaxis with CpG ODN did not significantly increase survival compared to the buffer group (60% vs. 45%, P = 0.2).

Conclusions

These findings suggest that systemic administration of CpG ODN may help to prevent bacterial CNS infections in immunocompromised individuals.

Efficacy of Ceftaroline Fosamil against Escherichia coli and Klebsiella pneumoniae strains in a rabbit meningitis model

In this study, the efficacy of ceftaroline fosamil was compared with that of cefepime in an experimental rabbit meningitis model against two Gram-negative strains (Escherichia coli QK-9 and Klebsiella pneumoniae 1173687). The penetration of ceftaroline into inflamed and uninflamed meninges was also investigated. Both regimens were bactericidal, but ceftaroline fosamil was significantly superior to cefepime against K. pneumoniae and E. coli in this experimental rabbit meningitis model (P < 0.0007 against K. pneumoniae and P < 0.0016 against E. coli). The penetration of ceftaroline was approximately 15% into inflamed meninges and approximately 3% into uninflamed meninges.

Cytotoxic necrotizing factor 1 contributes to Escherichia coli meningitis

E. coli is the most common Gram-negative bacteria causing neonatal meningitis, and E. coli meningitis continues to be an important cause of mortality and morbidity throughout the world. Recent reports of E. coli meningitis caused by antimicrobial resistant strains are a particular concern. These findings indicate that a novel strategy is needed to identify new targets for prevention and therapy of E. coli meningitis. Cytotoxic necrotizing factor 1 (CNF1) is a bacterial virulence factor associated principally with E. coli strains causing urinary tract infection and meningitis. We have shown that CNF1 contributes to E. coli invasion of the blood-brain barrier and penetration into the brain, the essential step in the development of E. coli meningitis, and identified the host receptor for CNF1, 37-kDa laminin receptor precursor (37LRP). CNF1, however, is a cytoplasmic protein and its contribution to E. coli invasion of the blood-brain barrier requires its secretion from the bacterial cytoplasm. No signal peptide is found in the CNF1 sequence. CNF1 secretion is, therefore, a strategy utilized by meningitis-causing E. coli to invade the blood-brain barrier. Elucidation of the mechanisms involved in CNF1 secretion, as shown in this report with the involvement of Fdx and YgfZ provides the novel information on potential targets for prevention and therapy of E. coli meningitis by virtue of targeting the secretion of CNF1.

[Virulence factors and pathophysiology of extraintestinal pathogenic Escherichia coli]

Extraintestinal pathogenic Escherichia coli (ExPEC) causing urinary tract infections, bacteraemia or meningitis are characterized by a particular genetic background (phylogenetic group B2 and D) and the presence, within genetic pathogenicity islands (PAI) or plasmids, of genes encoding virulence factors involved in adhesion to epithelia, crossing of the body barriers (digestive, kidney, bloodbrain), iron uptake and resistance to the immune system. Among the many virulence factors described, two are particularly linked with a pathophysiological process: type P pili PapGII adhesin is linked with acute pyelonephritis, in the absence of abnormal flow of urine, and the K1 capsule is linked with neonatal meningitis. However, if the adhesin PapGII appears as the key factor of pyelonephritis, such that its absence in strain causing the infection is predictive of malformation or a vesico-ureteral reflux, the meningeal virulence of E. coli can not be reduced to a single virulence factor, but results from a combination of factors unique to each clone, and an imbalance between the immune defenses of the host and bacterial virulence.

In vivo antimicrobial evaluation of an alanine-rich peptide derived from Pleuronectes americanus

In several organisms, the first barrier against microbial infections consists of antimicrobial peptides (AMPs) which are molecules that act as components of the innate immune system. Recent studies have demonstrated that AMPs can perform various functions in different tissues or physiological conditions. In this view, this study was carried out in order to evaluate the multifunctional activity in vivo of an alanine-rich peptide, known as Pa-MAP, derived from the polar fish Pleuronectes americanus. Pa-MAP was evaluated in intraperitoneally infected mice with a sub-lethal concentration of Escherichia coli at standard concentrations of 1 and 5 mg kg(-1). At both concentrations, Pa-MAPs exhibited an ability to prevent E. coli infection and increase mice survival, similar to the result observed in mice treated with ampicillin at 2 mg kg(-1). In addition, mice were monitored for weight loss. The results showed that mice treated with Pa-MAPs at 1 mg kg(-1) gained 0.8% of body weight during the 72 h of experiment. The same was observed with Pa-MAP at 5 mg kg(-1), which had a gain of 0.5% in body weight during the treatment. Mice treated with ampicillin at 2 mg kg(-1) show a significant weight loss of 5.6% of body weight. The untreated group exhibited a 5.5% loss of body weight. The immunomodulatory effects were also evaluated by the quantification of IL-10, IL-12, TNF-α, IFN-γ and nitric oxide cytokines in serum, but no immunomodulatory activity was observed. Data presented here suggest that Pa-MAP should be used as a novel antibiotic against infection control.

Resistance of the brain to Escherichia coli K1 infection depends on MyD88 signaling and the contribution of neutrophils and monocytes

Escherichia coli is the leading cause of Gram-negative neonatal bacterial meningitis and also causes meningitis and meningoencephalitis in older and immunocompromised patients. Here, we determined the contribution of granulocytes, monocytes, and TLR signaling cascades in the resistance of adult mice to Escherichia coli K1 brain infection. Deficiency in MyD88 (myd88(-/-)) but not in TRIF (trif(lps2)) adaptor proteins dramatically reduced the survival of animals. Depletion of CD11b(+) Ly-6G(+) Ly-6C(int) neutrophils by application of the anti-Ly-6G (1A8) monoclonal antibody (MAb) led to higher bacterial loads in cerebellum and spleen tissue and resulted in increased mortality compared to those of isotype-treated controls. Depletion of CD11b(+) Ly-6G(+) Ly-6C(int) neutrophils and CD11b(+) Ly-6G(-) Ly-6C(high) monocytes by administration of the anti-Gr-1 (RB6-8C5) MAb rendered mice even more susceptible to the infection, with higher central nervous system (CNS) and spleen bacterial burdens than anti-Ly-6G-treated animals. Depletion of ∼50% of CD11b(+) Ly-6G(-) Ly-6C(high) monocytes by injection of the anti-CCR2 (MC-21) MAb resulted in a trend toward higher mortality compared to that with isotype treatment. Production of interleukin 1β (IL-1β), IL-6, KC, and MIP-2 in the CNS strongly depended on the bacterial load: increased levels of these cytokines/chemokines were found after depletion of CD11b(+) Ly-6G(+) Ly-6C(int) neutrophils alone or together with CD11b(+) Ly-6G(-) Ly-6C(high) monocytes. These findings identify Toll-like receptor (TLR)-MyD88 signaling and neutrophil and monocyte activity as critical elements in the early host defense against E. coli meningitis.

Prevalence of genes encoding virulence factors among Escherichia coli with K1 antigen and non-K1 E. coli strains

Multiplex PCR was used to detect genes encoding selected virulence determinants associated with strains of Escherichia coli with K1 antigen (K1(+)) and non-K1 E. coli (K1(-)). The prevalence of the fimA, fimH, sfa/foc, ibeA, iutA and hlyF genes was studied for 134 (67 K1(+) and 67 K1(-)) E. coli strains isolated from pregnant women and neonates. The fimA gene was present in 83.6 % of E. coli K1(+) and in 86.6 % of E. coli K1(-) strains. The fimH gene was present in all tested E. coli K1(+) strains and in 97.0 % of non-K1 strains. E. coli K1(+) strains were significantly more likely to possess the following genes than E. coli K1(-) strains: sfa/foc (37.3 vs 16.4 %, P = 0.006), ibeA (35.8 vs 4.5 %, P<0.001), iutA (82.1 vs 35.8 %, P<0.001) and hlyF (28.4 vs 6.0 %, P<0.001). In conclusion, E. coli K1(+) seems to be more virulent than E. coli K1(-) strains in developing severe infections, thereby increasing possible sepsis or neonatal bacterial meningitis.

IbeA and OmpA of Escherichia coli K1 exploit Rac1 activation for invasion of human brain microvascular endothelial cells

Meningitis-causing Escherichia coli K1 internalization of the blood-brain barrier is required for penetration into the brain, but the host-microbial interactions involved in E. coli entry of the blood-brain barrier remain incompletely understood. We show here that a meningitis-causing E. coli K1 strain RS218 activates Rac1 (GTP-Rac1) of human brain microvascular endothelial cells (HBMEC) in a time-dependent manner. Both activation and bacterial invasion were significantly inhibited in the presence of a Rac1 inhibitor. We further showed that the guanine nucleotide exchange factor Vav2, not β-Pix, was involved in E. coli K1-mediated Rac1 activation. Since activated STAT3 is known to bind GTP-Rac1, the relationship between STAT3 and Rac1 was examined in E. coli K1 invasion of HBMEC. Downregulation of STAT3 resulted in significantly decreased E. coli invasion compared to control HBMEC, as well as a corresponding decrease in GTP-Rac1, suggesting that Rac1 activation in response to E. coli is under the control of STAT3. More importantly, two E. coli determinants contributing to HBMEC invasion, IbeA and OmpA, were shown to affect both Rac1 activation and their association with STAT3. These findings demonstrate for the first time that specific E. coli determinants regulate a novel mechanism of STAT3 cross talk with Rac1 in E. coli K1 invasion of HBMEC.

Toxoplasma gondii and the blood-brain barrier

Infection with the protozoan parasite Toxoplasma gondii is characterized by asymptomatic latent infection in the central nervous system and skeletal muscle tissue in the majority of immunocompentent individuals. Life-threatening reactivation of the infection in immunocompromized patients originates from rupture of Toxoplasma cysts in the brain. While major progress has been made in our understanding of the immunopathogenesis of infection the mechanism(s) of neuroinvasion of the parasite remains poorly understood. The present review presents the current understanding of blood-brain barrier (patho)physiology and the interaction of Toxoplasma gondii with cells of the blood-brain barrier.

Loss of outer membrane protein C in Escherichia coli contributes to both antibiotic resistance and escaping antibody-dependent bactericidal activity

Outer membrane proteins (OMPs) serve as the permeability channels for nutrients, toxins, and antibiotics. In Escherichia coli, OmpA has been shown to be involved in bacterial virulence, and OmpC is related to multidrug resistance. However, it is unclear whether OmpC also has a role in the virulence of E. coli. The aims of this study were to characterize the role of OmpC in antimicrobial resistance and bacterial virulence in E. coli. The ompC deletion mutant showed significantly decreased susceptibility to carbapenems and cefepime. To investigate the survival of E. coli exposed to the innate immune system, a human blood bactericidal assay showed that the ompC mutant increased survival in blood and serum but not in complement-inactivated serum. These effects were also demonstrated in the natural selection of OmpC mutants. Also, C1q interacted with E. coli through a complex of antibodies bound to OmpC as a major target. Bacterial survival was increased in the wild-type strain in a dose-dependent manner by adding free recombinant OmpC protein or anti-C1q antibody to human serum. These results demonstrated that the interaction of OmpC-specific antibody and C1q was the key step in initiating the antibody-dependent classical pathway for the clearance of OmpC-expressing E. coli. Anti-OmpC antibody was detected in human sera, indicating that OmpC is an immunogen. These data indicate that the loss of OmpC in E. coli is resistant to not only antibiotics, but also the serum bactericidal effect, which is mediated from the C1q and anti-OmpC antibody-dependent classical pathway.

Contribution of lethal toxin and edema toxin to the pathogenesis of anthrax meningitis

Bacillus anthracis is a Gram-positive spore-forming bacterium that causes anthrax disease in humans and animals. Systemic infection is characterized by septicemia, toxemia, and meningitis, the main neurological complication associated with high mortality. We have shown previously that B. anthracis Sterne is capable of blood-brain barrier (BBB) penetration, establishing the classic signs of meningitis, and that infection is dependent on the expression of both major anthrax toxins, lethal toxin (LT) and edema toxin (ET). Here we further investigate the contribution of the individual toxins to BBB disruption using isogenic toxin mutants deficient in lethal factor, ΔLF, and edema factor, ΔEF. Acute infection with B. anthracis Sterne and the ΔLF mutant resulted in disruption of human brain microvascular endothelial cell (hBMEC) monolayer integrity and tight junction protein zona occludens-1, while the result for cells infected with the ΔEF mutant was similar to that for the noninfected control. A significant decrease in bacterial invasion of BBB endothelium in vitro was observed during infection with the ΔLF strain, suggesting a prominent role for LT in promoting BBB interaction. Further, treatment of hBMECs with purified LT or chemicals that mimic LT action on host signaling pathways rescued the hypoinvasive phenotype of the ΔLF mutant and resulted in increased bacterial uptake. We also observed that toxin expression reduced bacterial intracellular survival by inducing the bulk degradative autophagy pathway in host cells. Finally, in a murine model of anthrax meningitis, mice infected with the ΔLF mutant exhibited no mortality, brain bacterial load, or evidence of meningitis compared to mice infected with the parental or ΔEF strains.

Intracellular transport of Toxoplasma gondii through the blood-brain barrier

Toxoplasma gondii establishes latent infection in the central nervous system of immunocompentent hosts. Toxoplasmic encephalitis is a life threatening reactivation of latent infection in the brain of immunocompromised patients. To further understand the mechanisms of entry into the brain of T. gondii we investigated host molecules and cells involved in the passage of the parasite through the blood-brain barrier. First, using microarrays brain endothelial cells were found to upregulate, among others, chemokines and adhesion molecules following infection with tachyzoites. Using flow cytometry we observed upregulated ICAM-1 expression on the surface of brain endothelial cells following infection; ICAM-1 expression was further increased after pre-incubation with IFN-γ. Compared to RH tachyzoites, ME49 tachyzoites induced a stronger upregulation of ICAM-1 and an earlier and stronger IL-6 and MCP-1 secretion by brain endothelial cells. Using an in vitro coculture model of the BBB (primary glia cells and brain endothelial cells) we found a stronger migration of infected antigen-presenting cells compared to lymphocytes (4.63% vs. 0.6% of all cells) across the BBB. Among all antigen-presenting cells CD11b(+)/CD11c(+) cells showed the highest infection rate, whereas the majority of infected cells that migrated through the blood-brain barrier were CD11b(+)/CD11c(-) cells. Infection of PBMCs with type I or type II Toxoplasma strains resulted in similar patterns of cell migration across the in vitro BBB model. In conclusion, these results suggest that T. gondii modulates gene expression of brain endothelial cells to promote its own migration through the blood-brain barrier in a 'Trojan horse' manner. Cells expressing CD11b either with or without CD11c are likely candidate cells for the intracellular transport of T. gondii across the BBB. T. gondii type I and type II strains induced similar migration patterns of antigen-presenting cells across the in vitro BBB.