Vascular colonization by Neisseria meningitidis

Microbial communities, antibiotic resistance genes, and virulence factors in urinary infectious stone-associated urinary tract infections

Urinary infectious stones are challenging due to bacterial involvement, necessitating a comprehensive understanding of these conditions. Antibiotic-resistant urease-producing bacteria further complicate clinical management. In this study, analysis of urine and stone samples from urinary tract infection (UTI) patients revealed microbial shifts, gene enrichment in stones, and metabolic pathway disparities; antibiotic resistance gene trends were phylum-specific, urease-producing bacteria are at risk of acquiring AMR carried by Enterobacteriaceae under antibiotic, emphasizing potential AMR dissemination between them; Correlations of key pathogenic species in kidney stone and urine microbial communities highlight the need for targeted therapeutic strategies to manage complexities in UTIs; Stones and urine contain a variety of deleterious genes even before antibiotic use, and piperacillin/tazobactam better reduced the abundance of antibiotic resistance genes in stones and urine. The presence of diverse antibiotic resistance and virulence genes underscores challenges in clinical management and emphasizes the need for effective treatment strategies to mitigate risks associated with UTIs and urinary infectious stone formation. Ongoing research is vital for advancing knowledge and developing innovative approaches to address these urological conditions.

Microbiological Analysis and Mortality Risk Factors in Patients with Polymicrobial Bloodstream Infections

Purpose

To study the etiological characteristics and risk factors affecting the prognosis of patients with polymicrobial bloodstream infections.

Patients and Methods

Overall, 141 patients with polymicrobial bloodstream infections in Henan Provincial People's Hospital during 2021 were included. Laboratory test indexes, department of admission, sex, age, intensive care unit (ICU) admission, surgical history, and central venous catheter placement were collected. Patients were divided into surviving and deceased groups based on outcomes at discharge. Mortality risk factors were identified by univariate and multivariable analyses.

Results

Seventy-two of 141 patients survived. Patients were mainly from the ICU and the Departments of Hepatobiliary Surgery and Hematology. Overall, 312 microbial strains were detected: 119 gram-positive, 152 gram-negative, and 13 anaerobic bacteria and 28 fungi. Among the gram-positive bacteria, coagulase-negative staphylococci were most frequent (44/119, 37%), followed by enterococci (35/119, 29.4%). Among coagulase-negative staphylococci, methicillin-resistant coagulase-negative staphylococci incidence was 75% (33/44). Among gram-negative bacteria, Klebsiella pneumoniae was most common (45/152, 29.6%), followed by Escherichia coli (25/152, 16.4%) and Pseudomonas aeruginosa (13/152, 8.6%). Among K. pneumoniae, the incidence of carbapenem-resistant (CR) K. pneumoniae was 45.7% (21/45). On univariate analysis, mortality risk factors included increased white blood cells and C-reactive protein, decreased total protein and albumin, CR strains, ICU admission, central venous catheter, multiple organ failure, sepsis, shock, pulmonary diseases, respiratory failure, central nervous system diseases, cardiovascular diseases, hypoproteinemia, and electrolyte disturbances (P < 0.05). Multivariable analysis showed that ICU admission, shock, electrolyte disorders, and central nervous system diseases were independent mortality risk factors. The survival curve shows that the survival rate of patients with polymicrobial CR bloodstream infections was lower than that of patients with polymicrobial non-CR bloodstream infections (P=0.029).

Conclusion

Patients with polymicrobial bloodstream infections are typically critically ill and harbor multidrug-resistant bacteria. Thus, to minimize mortality rate in critically ill patients, changes in infectious flora should be monitored, antibiotics selected reasonably, and invasive procedures reduced.

Type IV pilus retraction enables sustained bacteremia and plays a key role in the outcome of meningococcal sepsis in a humanized mouse model

Neisseria meningitidis (the meningococcus) remains a major cause of bacterial meningitis and fatal sepsis. This commensal bacterium of the human nasopharynx can cause invasive diseases when it leaves its niche and reaches the bloodstream. Blood-borne meningococci have the ability to adhere to human endothelial cells and rapidly colonize microvessels. This crucial step enables dissemination into tissues and promotes deregulated inflammation and coagulation, leading to extensive necrotic purpura in the most severe cases. Adhesion to blood vessels relies on type IV pili (TFP). These long filamentous structures are highly dynamic as they can rapidly elongate and retract by the antagonistic action of two ATPases, PilF and PilT. However, the consequences of TFP dynamics on the pathophysiology and the outcome of meningococcal sepsis in vivo have been poorly studied. Here, we show that human graft microvessels are replicative niches for meningococci, that seed the bloodstream and promote sustained bacteremia and lethality in a humanized mouse model. Intriguingly, although pilus-retraction deficient N. meningitidis strain (ΔpilT) efficiently colonizes human graft tissue, this mutant did not promote sustained bacteremia nor induce mouse lethality. This effect was not due to a decreased inflammatory response, nor defects in bacterial clearance by the innate immune system. Rather, TFP-retraction was necessary to promote the release of TFP-dependent contacts between bacteria and, in turn, the detachment from colonized microvessels. The resulting sustained bacteremia was directly correlated with lethality. Altogether, these results demonstrate that pilus retraction plays a key role in the occurrence and outcome of meningococcal sepsis by supporting sustained bacteremia. These findings open new perspectives on the role of circulating bacteria in the pathological alterations leading to lethal sepsis.

Super-Resolution Microscopy Reveals Local Accumulation of Plasma Membrane Gangliosides at Neisseria meningitidis Invasion Sites

Neisseria meningitidis (meningococcus) is a Gram-negative bacterium responsible for epidemic meningitis and sepsis worldwide. A critical step in the development of meningitis is the interaction of bacteria with cells forming the blood-cerebrospinal fluid barrier, which requires tight adhesion of the pathogen to highly specialized brain endothelial cells. Two endothelial receptors, CD147 and the β2-adrenergic receptor, have been found to be sequentially recruited by meningococci involving the interaction with type IV pilus. Despite the identification of cellular key players in bacterial adhesion the detailed mechanism of invasion is still poorly understood. Here, we investigated cellular dynamics and mobility of the type IV pilus receptor CD147 upon treatment with pili enriched fractions and specific antibodies directed against two extracellular Ig-like domains in living human brain microvascular endothelial cells. Modulation of CD147 mobility after ligand binding revealed by single-molecule tracking experiments demonstrates receptor activation and indicates plasma membrane rearrangements. Exploiting the binding of Shiga (STxB) and Cholera toxin B (CTxB) subunits to the two native plasma membrane sphingolipids globotriaosylceramide (Gb3) and raft-associated monosialotetrahexosylganglioside GM1, respectively, we investigated their involvement in bacterial invasion by super-resolution microscopy. Structured illumination microscopy (SIM) and direct stochastic optical reconstruction microscopy (dSTORM) unraveled accumulation and coating of meningococci with GM1 upon cellular uptake. Blocking of CTxB binding sites did not impair bacterial adhesion but dramatically reduced bacterial invasion efficiency. In addition, cell cycle arrest in G1 phase induced by serum starvation led to an overall increase of GM1 molecules in the plasma membrane and consequently also in bacterial invasion efficiency. Our results will help to understand downstream signaling events after initial type IV pilus-host cell interactions and thus have general impact on the development of new therapeutics targeting key molecules involved in infection.

Adhesion to nanofibers drives cell membrane remodeling through one-dimensional wetting

The shape of cellular membranes is highly regulated by a set of conserved mechanisms that can be manipulated by bacterial pathogens to infect cells. Remodeling of the plasma membrane of endothelial cells by the bacterium Neisseria meningitidis is thought to be essential during the blood phase of meningococcal infection, but the underlying mechanisms are unclear. Here we show that plasma membrane remodeling occurs independently of F-actin, along meningococcal type IV pili fibers, by a physical mechanism that we term 'one-dimensional' membrane wetting. We provide a theoretical model that describes the physical basis of one-dimensional wetting and show that this mechanism occurs in model membranes interacting with nanofibers, and in human cells interacting with extracellular matrix meshworks. We propose one-dimensional wetting as a new general principle driving the interaction of cells with their environment at the nanoscale that is diverted by meningococci during infection.

Mechanisms of Blood Brain Barrier Disruption by Different Types of Bacteria, and Bacterial-Host Interactions Facilitate the Bacterial Pathogen Invading the Brain

This review aims to elucidate the different mechanisms of blood brain barrier (BBB) disruption that may occur due to invasion by different types of bacteria, as well as to show the bacteria-host interactions that assist the bacterial pathogen in invading the brain. For example, platelet-activating factor receptor (PAFR) is responsible for brain invasion during the adhesion of pneumococci to brain endothelial cells, which might lead to brain invasion. Additionally, the major adhesin of the pneumococcal pilus-1, RrgA is able to bind the BBB endothelial receptors: polymeric immunoglobulin receptor (pIgR) and platelet endothelial cell adhesion molecule (PECAM-1), thus leading to invasion of the brain. Moreover, Streptococcus pneumoniae choline binding protein A (CbpA) targets the common carboxy-terminal domain of the laminin receptor (LR) establishing initial contact with brain endothelium that might result in BBB invasion. Furthermore, BBB disruption may occur by S. pneumoniae penetration through increasing in pro-inflammatory markers and endothelial permeability. In contrast, adhesion, invasion, and translocation through or between endothelial cells can be done by S. pneumoniae without any disruption to the vascular endothelium, upon BBB penetration. Internalins (InlA and InlB) of Listeria monocytogenes interact with its cellular receptors E-cadherin and mesenchymal-epithelial transition (MET) to facilitate invading the brain. L. monocytogenes species activate NF-κB in endothelial cells, encouraging the expression of P- and E-selectin, intercellular adhesion molecule 1 (ICAM-1), and Vascular cell adhesion protein 1 (VCAM-1), as well as IL-6 and IL-8 and monocyte chemoattractant protein-1 (MCP-1), all these markers assist in BBB disruption. Bacillus anthracis species interrupt both adherens junctions (AJs) and tight junctions (TJs), leading to BBB disruption. Brain microvascular endothelial cells (BMECs) permeability and BBB disruption are induced via interendothelial junction proteins reduction as well as up-regulation of IL-1α, IL-1β, IL-6, TNF-α, MCP-1, macrophage inflammatory proteins-1 alpha (MIP1α) markers in Staphylococcus aureus species. Streptococcus agalactiae or Group B Streptococcus toxins (GBS) enhance IL-8 and ICAM-1 as well as nitric oxide (NO) production from endothelial cells via the expression of inducible nitric oxide synthase (iNOS) enhancement, resulting in BBB disruption. While Gram-negative bacteria, Haemophilus influenza OmpP2 is able to target the common carboxy-terminal domain of LR to start initial interaction with brain endothelium, then invade the brain. H. influenza type b (HiB), can induce BBB permeability through TJ disruption. LR and PAFR binding sites have been recognized as common routes of CNS entrance by Neisseria meningitidis. N. meningitidis species also initiate binding to BMECs and induces AJs deformation, as well as inducing specific cleavage of the TJ component occludin through the release of host MMP-8. Escherichia coli bind to BMECs through LR, resulting in IL-6 and IL-8 release and iNOS production, as well as resulting in disassembly of TJs between endothelial cells, facilitating BBB disruption. Therefore, obtaining knowledge of BBB disruption by different types of bacterial species will provide a picture of how the bacteria enter the central nervous system (CNS) which might support the discovery of therapeutic strategies for each bacteria to control and manage infection.

Development of a DNA Aptamer for Screening Neisseria meningitidis Serogroup B by Cell SELEX

Background

Artificial oligonucleotides like DNA or RNA aptamers can be used as biodiagnostic alternatives for antibodies to detect pathogens. Comparing to antibodies, artificial oligonucleotides are produced easily at lower costs and are more stable. Neisseria meningitidis, the causative agent of meningitis, is responsible for about 1% of infections in an epidemic period. Specific DNA aptamers that bind to N. meningitidis serogroup B were identified by whole-cell Systemic Evolution of Ligands by EXponential Enrichment (SELEX).

Methods

The SELEX begins with a library of labeled ssDNA molecules. After six rounds of selection and two rounds of counter-selection, 60 clones were obtained, of which the binding efficiency of 21 aptamers to the aforementioned bacterium was tested by flow cytometry.

Results

The aptamers K3 and K4 showed the highest affinity to N. meningitidis serogroup B and no affinity to N. meningitidis serogroups Y, A, and C, or to other meningitis causing bacteria. The dissociation constant (Kd value) for K3 and K4 were calculated as 28.3±8.9 pM and 39.1±8.6 pM, respectively. K3 aptamer with the lowest Kd was chosen as the main aptamer. K3 could detect N. meningitidis in patients’ cerebrospinal fluid (CSF) samples and in CSF from healthy volunteers inoculated with N. meningitidis serogroup B (ATCC 13090) at 200 and 100 CFU ml-1, respectively.

Conclusion

The findings suggest the application of the developed aptamer in specific detection of N. meningitidis serogroup B amongst a group of meningitis causing bacteria.

Inactivation of human coagulation factor X by a protease of the pathogen Capnocytophaga canimorsus

Essentials Capnocytophaga canimorsus causes severe dog bite related blood stream infections. We investigated if C. canimorsus contributes to bleeding abnormalities during infection. The C. canimorsus protease CcDPP7 causes factor X dysfunction by N-terminal cleavage. CcDPP7 inhibits coagulation in vivo, which could promote immune evasion and trigger hemorrhage.

SUMMARY

Background Capnocytophaga canimorsus is a Gram-negative bacterium that is present in the oral flora of dogs and causes fulminant sepsis in humans who have been bitten, licked, or scratched. In patients, bleeding abnormalities, such as petechiae, purpura fulminans, or disseminated intravascular coagulation (DIC), occur frequently. Objective To investigate whether C. canimorsus could actively contribute to these bleeding abnormalities. Methods Calibrated automated thrombogram and clotting time assays were performed to assess the anticoagulant activity of C. canimorsus 5 (Cc5), a strain isolated from a fatal human infection. Clotting factor activities were measured with factor-deficient plasma. Factor X cleavage was monitored with the radiolabeled zymogen and western blotting. Mutagenesis of Cc5 genes encoding putative serine proteases was performed to identify the protease that cleaves FX. Protein purification was performed with affinity chromatography. Edman degradation allowed the detection of N-terminal cleavage of FX. Tail bleeding times were measured in mice. Results We found that Cc5 inhibited thrombin generation and increased the prothrombin time and the activated partial thromboplastin time of human plasma via FX cleavage. A mutant that was unable to synthesize a type 7 dipeptidyl peptidase (DPP7) of the S46 serine protease family failed to proteolyse FX. The purified protease (CcDPP7) cleaved FX heavy and light chains from the N-terminus, and was active in vivo after intravenous injection. Conclusions This is, to our knowledge, the first study demonstrating a detailed mechanism for FX inactivation by a bacterial protease, and it is the first functional study associating DPP7 proteases with a potentially pathogenic outcome.

Microbial pathogenesis meets biomechanics

Introducing concepts from soft matter physics and mechanics has largely contributed to our understanding of a variety of biological processes. In this review, we argue that this holds true for bacterial pathogenesis. We base this argument on three examples of bacterial pathogens and their interaction with host cells during infection: (i) Shigella flexneri exploits actin-dependent forces to come into close contact with epithelial cells prior to invasion of the epithelium; (ii) Neisseria meningitidis manipulates endothelial cells to resist shear stress during vascular colonization; (iii) bacterial toxins take advantage of the biophysical properties of the host cell plasma membrane to generate transcellular macroapertures in the vascular wall. Together, these examples show that a multidisciplinary approach integrating physics and biology is more necessary than ever to understand complex infectious phenomena. Moreover, this avenue of research will allow the exploration of general processes in cell biology, highlighted by pathogens, in the context of other non-communicable human diseases.

A critical role for ATF2 transcription factor in the regulation of E-selectin expression in response to non-endotoxin components of Neisseria meningitidis

Vascular injury is a serious complication of sepsis due to the gram‐negative bacterium Neisseria meningitidis. One of the critical early steps in initiating this injury is via the interaction of leucocytes, particularly neutrophils, with adhesion molecules expressed on inflamed endothelium. We have previously demonstrated that both lipopolysaccharide (LPS) and non‐LPS components of meningococci can induce very high levels of expression of the vascular endothelial cell adhesion molecule E‐selectin, which is critical for early tethering and capture of neutrophils onto endothelium under flow. Using an LPS‐deficient strain of meningococcus, we showed that very high levels of expression can be induced in primary endothelial cells, even in the context of weak activation of the major host signal transduction factor [nuclear factor‐κB (NF‐κB)]. In this study, we show that the particular propensity for N. meningitidis to induce high levels of expression is regulated at a transcriptional level, and demonstrate a significant role for phosphorylation of the ATF2 transcription factor, likely via mitogen‐activated protein (MAP) kinases, on the activity of the E‐selectin promoter. Furthermore, inhibition of E‐selectin expression in response to the lpxA− strain by a p38 inhibitor indicates a significant role of a p38‐dependent MAPK signalling pathway in ATF2 activation. Collectively, these data highlight the role that LPS and other bacterial components have in modulating endothelial function and their involvement in the pathogenesis of meningococcal sepsis. Better understanding of these multiple mechanisms induced by complex stimuli such as bacteria, and the specific inflammatory pathways they activate, may lead to improved, focused interventions in both meningococcal and potentially bacterial sepsis more generally.

How bacterial pathogens colonize their hosts and invade deeper tissues

Bacterial pathogens have evolved a wide range of strategies to colonize and invade human organs, despite the presence of multiple host defense mechanisms. In this review, we will describe how pathogenic bacteria can adhere and multiply at the surface of host cells, how some bacteria can enter and proliferate inside these cells, and finally how pathogens may cross epithelial or endothelial host barriers and get access to internal tissues, leading to severe diseases in humans.

Inhibition of matrix metalloproteinases attenuates brain damage in experimental meningococcal meningitis

BACKGROUND

Approximately 7% of survivors from meningococcal meningitis (MM) suffer from neurological sequelae due to brain damage in the course of meningitis. The present study focuses on the role of matrix metalloproteinases (MMPs) in a novel mouse model of MM-induced brain damage.

METHODS

The model is based on intracisternal infection of BALB/c mice with a serogroup C Neisseria meningitidis strain. Mice were infected with meningococci and randomised for treatment with the MMP inhibitor batimastat (BB-94) or vehicle. Animal survival, brain injury and host-response biomarkers were assessed 48 h after meningococcal challenge.

RESULTS

Mice that received BB-94 presented significantly diminished MMP-9 levels (p < 0.01), intracerebral bleeding (p < 0.01), and blood-brain barrier (BBB) breakdown (p < 0.05) in comparison with untreated animals. In mice suffering from MM, the amount of MMP-9 measured by zymography significantly correlated with both intracerebral haemorrhage (p < 0.01) and BBB disruption (p < 0.05).

CONCLUSIONS

MMPs significantly contribute to brain damage associated with experimental MM. Inhibition of MMPs reduces intracranial complications in mice suffering from MM, representing a potential adjuvant strategy in MM post-infection sequelae.

Pathogenic Neisseria meningitidis utilizes CD147 for vascular colonization

Neisseria meningitidis is a cause of meningitis epidemics worldwide and of rapidly progressing fatal septic shock. A crucial step in the pathogenesis of invasive meningococcal infections is the adhesion of bloodborne meningococci to both peripheral and brain endothelia, leading to major vascular dysfunction. Initial adhesion of pathogenic strains to endothelial cells relies on meningococcal type IV pili, but the endothelial receptor for bacterial adhesion remains unknown. Here, we report that the immunoglobulin superfamily member CD147 (also called extracellular matrix metalloproteinase inducer (EMMPRIN) or Basigin) is a critical host receptor for the meningococcal pilus components PilE and PilV. Interfering with this interaction potently inhibited the primary attachment of meningococci to human endothelial cells in vitro and prevented colonization of vessels in human brain tissue explants ex vivo and in humanized mice in vivo. These findings establish the molecular events by which meningococci target human endothelia, and they open new perspectives for treatment and prevention of meningococcus-induced vascular dysfunctions.

A combined mass spectrometry strategy for complete posttranslational modification mapping of Neisseria meningitidis major pilin

Herein, we report a new approach, based on the combination of mass profiling and tandem mass spectrometry, to address the issue of localising all post-translational modifications (PTMs) on the major pilin protein PiIE expressed by the pathogenic Neisseria species. PilE is the main component of type IV pili; filamentous organelles expressed at the surface of many bacterial pathogens and important virulence factors. Previous reports have shown that PilE can harbour various combinations of PTMs and have established strong links between PTM and pathogenesis. Complete PTM mapping of proteins involved in bacterial infection is therefore highly desirable. The methodology we propose here allowed us to fully characterise the PilE proteoforms of Neisseria meningitidis strain 8013, definitively identifying all PTMs present on all proteoforms and localising their position on the protein backbone. These modifications include a processed and methylated N-terminus, disulfide bridge, glycosylation and glycerophosphorylation at two different sites. A key element of our approach is high resolution, intact mass measurement of the proteoforms, a piece of information completely lacking in all classical bottom-up proteomics strategies used for PTM analysis and without which it is difficult to ensure complete PTM mapping.

Transmigration of polymorphnuclear neutrophils and monocytes through the human blood-cerebrospinal fluid barrier after bacterial infection in vitro

Background

Bacterial invasion through the blood-cerebrospinal fluid barrier (BCSFB) during bacterial meningitis causes secretion of proinflammatory cytokines/chemokines followed by the recruitment of leukocytes into the CNS. In this study, we analyzed the cellular and molecular mechanisms of polymorphonuclear neutrophil (PMN) and monocyte transepithelial transmigration (TM) across the BCSFB after bacterial infection.

Methods

Using an inverted transwell filter system of human choroid plexus papilloma cells (HIBCPP), we studied leukocyte TM rates, the migration route by immunofluorescence, transmission electron microscopy and focused ion beam/scanning electron microscopy, the secretion of cytokines/chemokines by cytokine bead array and posttranslational modification of the signal regulatory protein (SIRP) α via western blot.

Results

PMNs showed a significantly increased TM across HIBCPP after infection with wild-type Neisseria meningitidis (MC58). In contrast, a significantly decreased monocyte transmigration rate after bacterial infection of HIBCPP could be observed. Interestingly, in co-culture experiments with PMNs and monocytes, TM of monocytes was significantly enhanced. Analysis of paracellular permeability and transepithelial electrical resistance confirmed an intact barrier function during leukocyte TM. With the help of the different imaging techniques we could provide evidence for para- as well as for transcellular migrating leukocytes. Further analysis of secreted cytokines/chemokines showed a distinct pattern after stimulation and transmigration of PMNs and monocytes. Moreover, the transmembrane glycoprotein SIRPα was deglycosylated in monocytes, but not in PMNs, after bacterial infection.

Conclusions

Our findings demonstrate that PMNs and monoctyes differentially migrate in a human BCSFB model after bacterial infection. Cytokines and chemokines as well as transmembrane proteins such as SIRPα may be involved in this process.

Adhesion of Neisseria meningitidis to dermal vessels leads to local vascular damage and purpura in a humanized mouse model

Septic shock caused by Neisseria meningitidis is typically rapidly evolving and often fatal despite antibiotic therapy. Further understanding of the mechanisms underlying the disease is necessary to reduce fatality rates. Postmortem samples from the characteristic purpuric rashes of the infection show bacterial aggregates in close association with microvessel endothelium but the species specificity of N. meningitidis has previously hindered the development of an in vivo model to study the role of adhesion on disease progression. Here we introduced human dermal microvessels into SCID/Beige mice by xenografting human skin. Bacteria injected intravenously exclusively associated with the human vessel endothelium in the skin graft. Infection was accompanied by a potent inflammatory response with the secretion of human inflammatory cytokines and recruitment of inflammatory cells. Importantly, infection also led to local vascular damage with hemostasis, thrombosis, vascular leakage and finally purpura in the grafted skin, replicating the clinical presentation for the first time in an animal model. The adhesive properties of the type IV pili of N. meningitidis were found to be the main mediator of association with the dermal microvessels in vivo. Bacterial mutants with altered type IV pili function also did not trigger inflammation or lead to vascular damage. This work demonstrates that local type IV pili mediated adhesion of N. meningitidis to the vascular wall, as opposed to circulating bacteria, determines vascular dysfunction in meningococcemia.