Low-phosphate-dependent invasion resembles a general way for Neisseria gonorrhoeae to enter host cells

Gonococcal PorB: a multifaceted modulator of host immune responses

Neisseria gonorrhoeae is a human-specific pathogen responsible for the sexually transmitted infection, gonorrhoea. N. gonorrhoeae promotes its survival by manipulating both innate and adaptive immune responses. The most abundant gonococcal outer-membrane protein is PorB, an essential porin that facilitates ion exchange. Importantly, gonococcal PorB has several immunomodulatory properties. To subvert the innate immune response, PorB suppresses killing mechanisms of macrophages and neutrophils, and recruits negative regulators of complement to the gonococcal cell surface. For manipulation of adaptive immune responses, gonococcal PorB suppresses the capability of dendritic cells to stimulate proliferation of T cells. As gonococcal PorB is highly abundant in outer-membrane vesicles, consideration of the immunomodulatory properties of this porin is critical when designing gonococcal vaccines.

Neisseria gonorrhoeae vaccines: a contemporary overview

Neisseria gonorrhoeae infection is an important public health issue, with an annual global incidence of 87 million. N. gonorrhoeae infection causes significant morbidity and can have serious long-term impacts on reproductive and neonatal health and may rarely cause life-threatening disease. Global rates of N. gonorrhoeae infection have increased over the past 20 years. Importantly, rates of antimicrobial resistance to key antimicrobials also continue to increase, with the United States Centers for Disease Control and Prevention identifying drug-resistant N. gonorrhoeae as an urgent threat to public health. This review summarizes the current evidence for N. gonorrhoeae vaccines, including historical clinical trials, key N. gonorrhoeae vaccine preclinical studies, and studies of the impact of Neisseria meningitidis vaccines on N. gonorrhoeae infection. A comprehensive survey of potential vaccine antigens, including those identified through traditional vaccine immunogenicity approaches, as well as those identified using more contemporary reverse vaccinology approaches, are also described. Finally, the potential epidemiological impacts of a N. gonorrhoeae vaccine and research priorities for further vaccine development are described.

Sexually Transmitted Neisseria gonorrhoeae Infections-Update on Drug Treatment and Vaccine Development

Background: Sexually transmitted gonorrhea, caused by the Gram-negative diplococcus Neisseria gonorrhoeae, continues to be a serious global health challenge despite efforts to eradicate it. Multidrug resistance among clinical N. gonorrhoeae isolates has limited treatment options, and attempts to develop vaccines have not been successful. Methods: A search of published literature was conducted, and information extracted to provide an update on the status of therapeutics and vaccine development for gonorrheal infection. Results: Recommended pharmacological treatment for gonorrhea has changed multiple times due to increasing acquisition of resistance to existing antibiotics by N. gonorrhoeae. Only broad-spectrum cephalosporin-based combination therapies are currently recommended for treatment of uncomplicated urogenital and anorectal gonococcal infections. With the reported emergence of ceftriaxone resistance, successful strategies addressing the global burden of gonorrhea must include vaccination. Century-old efforts at developing an effective vaccine against gonorrhea, leading to only four clinical trials, have not yielded any successful vaccine. Conclusions: While it is important to continue to explore new drugs for the treatment of gonorrhea, the historical trend of resistance acquisition suggests that any long-term strategy should include vaccine development. Advanced technologies in proteomics and in silico approaches to vaccine target identification may provide templates for future success.

Folliculin Controls the Intracellular Survival and Trans-Epithelial Passage of Neisseria gonorrhoeae

Neisseria gonorrhoeae, a Gram-negative obligate human pathogenic bacterium, infects human epithelial cells and causes sexually transmitted diseases. Emerging multi-antibiotic resistant gonococci and increasing numbers of infections complicate the treatment of infected patients. Here, we used an shRNA library screen and next-generation sequencing to identify factors involved in epithelial cell infection. Folliculin (FLCN), a 64 kDa protein with a tumor repressor function was identified as a novel host factor important for N. gonorrhoeae survival after uptake. We further determined that FLCN did not affect N. gonorrhoeae adherence and invasion but was essential for its survival in the cells by modulating autophagy. In addition, FLCN was also required to maintain cell to cell contacts in the epithelial layer. In an infection model with polarized cells, FLCN inhibited the polarized localization of E-cadherin and the transcytosis of gonococci across polarized epithelial cells. In conclusion, we demonstrate here the connection between FLCN and bacterial infection and in particular the role of FLCN in the intracellular survival and transcytosis of gonococci across polarized epithelial cell layers.

A Role of Sphingosine in the Intracellular Survival of Neisseria gonorrhoeae

Obligate human pathogenic Neisseria gonorrhoeae are the second most frequent bacterial cause of sexually transmitted diseases. These bacteria invade different mucosal tissues and occasionally disseminate into the bloodstream. Invasion into epithelial cells requires the activation of host cell receptors by the formation of ceramide-rich platforms. Here, we investigated the role of sphingosine in the invasion and intracellular survival of gonococci. Sphingosine exhibited an anti-gonococcal activity in vitro. We used specific sphingosine analogs and click chemistry to visualize sphingosine in infected cells. Sphingosine localized to the membrane of intracellular gonococci. Inhibitor studies and the application of a sphingosine derivative indicated that increased sphingosine levels reduced the intracellular survival of gonococci. We demonstrate here, that sphingosine can target intracellular bacteria and may therefore exert a direct bactericidal effect inside cells.

Progress Toward a Gonococcal Vaccine: The Way Forward

The concept of immunizing against gonorrhea has received renewed interest because of the recent emergence of strains of Neisseria gonorrhoeae that are resistant to most currently available antibiotics, an occurrence that threatens to render gonorrhea untreatable. However, despite efforts over many decades, no vaccine has yet been successfully developed for human use, leading to pessimism over whether this goal was actually attainable. Several factors have contributed to this situation, including extensive variation of the expression and specificity of many of the gonococcal surface antigens, and the ability of N. gonorrhoeae to resist destruction by complement and other innate immune defense mechanisms. The natural host restriction of N. gonorrhoeae for humans, coupled with the absence of any definable state of immunity arising from an episode of gonorrhea, have also complicated efforts to study gonococcal pathogenesis and the host's immune responses. However, recent findings have elucidated how the gonococcus exploits and manipulates the host's immune system for its own benefit, utilizing human-specific receptors for attachment to and invasion of tissues, and subverting adaptive immune responses that might otherwise be capable of eliminating it. While no single experimental model is capable of providing all the answers, experiments utilizing human cells and tissues in vitro, various in vivo animal models, including genetically modified strains of mice, and both experimental and observational human clinical studies, have combined to yield important new insight into the immuno-pathogenesis of gonococcal infection. In turn, these have now led to novel approaches for the development of a gonococcal vaccine. Ongoing investigations utilizing all available tools are now poised to make the development of an effective human vaccine against gonorrhea an achievable goal within a foreseeable time-frame.

Diverse Facets of Sphingolipid Involvement in Bacterial Infections

Sphingolipids are constituents of the cell membrane that perform various tasks as structural elements and signaling molecules, in addition to regulating many important cellular processes, such as apoptosis and autophagy. In recent years, it has become increasingly clear that sphingolipids and sphingolipid signaling play a vital role in infection processes. In many cases the attachment and uptake of pathogenic bacteria, as well as bacterial development and survival within the host cell depend on sphingolipids. In addition, sphingolipids can serve as antimicrobials, inhibiting bacterial growth and formation of biofilms. This review will give an overview of our current information about these various aspects of sphingolipid involvement in bacterial infections.

Biomimetic Human Tissue Model for Long-Term Study of Neisseria gonorrhoeae Infection

Gonorrhea is the second most common sexually transmitted infection in the world and is caused by Gram-negative diplococcus Neisseria gonorrhoeae. Since N. gonorrhoeae is a human-specific pathogen, animal infection models are only of limited use. Therefore, a suitable in vitro cell culture model for studying the complete infection including adhesion, transmigration and transport to deeper tissue layers is required. In the present study, we generated three independent 3D tissue models based on porcine small intestinal submucosa (SIS) scaffold by co-culturing human dermal fibroblasts with human colorectal carcinoma, endometrial epithelial, and male uroepithelial cells. Functional analyses such as transepithelial electrical resistance (TEER) and FITC-dextran assay indicated the high barrier integrity of the created monolayer. The histological, immunohistochemical, and ultra-structural analyses showed that the 3D SIS scaffold-based models closely mimic the main characteristics of the site of gonococcal infection in human host including the epithelial monolayer, the underlying connective tissue, mucus production, tight junction, and microvilli formation. We infected the established 3D tissue models with different N. gonorrhoeae strains and derivatives presenting various phenotypes regarding adhesion and invasion. The results indicated that the disruption of tight junctions and increase in interleukin production in response to the infection is strain and cell type-dependent. In addition, the models supported bacterial survival and proved to be better suitable for studying infection over the course of several days in comparison to commonly used Transwell® models. This was primarily due to increased resilience of the SIS scaffold models to infection in terms of changes in permeability, cell destruction and bacterial transmigration. In summary, the SIS scaffold-based 3D tissue models of human mucosal tissues represent promising tools for investigating N. gonorrhoeae infections under close-to-natural conditions.

The Role of Meningococcal Porin B in Protein-Protein Interactions with Host Cells

Neisseria meningitidis is a Gram-negative diplococcus responsible for bacterial meningitis and fatal sepsis. Ligand-receptor interactions are one of the main steps in the development of neuroinvasion. Porin B (PorB), neisserial outer membrane protein (ligand), binds to host receptors and triggers many cell signalling cascades allowing the meningococcus to damage the host cells or induce immune cells responses via the TLR2-dependent mechanisms. In this paper, we present a brief review of the structure and function of PorB.

Neisseriae internalization by epithelial cells is enhanced by TLR2 stimulation

Neisseria meningitidis (NM) is an opportunistic gram-negative human pathogen that colonizes the human nasopharyngeal epithelium. Asymptomatic carriage is common, but some meningococcal strains can invade nasopharyngeal epithelial cells and proceed to cause severe and often fatal infections. Invasion is predominantly driven by expression of bacterial virulence factors and host cell cognate receptors for bacterial recognition. Porins are among the Neisserial components involved in host cell activation and bacterial internalization processes. Similar to other virulence factors, porins present antigenic and structure variability among strains. Such sequence variability in the surface-exposed loop regions has been correlated to bacterial invasiveness and to variability in host cell responses via Toll-like receptor 2 (TLR2). Here, we examined whether TLR2 signaling by porins influences recovery of intracellular Neisseriae from epithelial cells in vitro. Our results show that TLR2 stimulation, either by the organism or exogenously, generally enhances Neisseriae internalization by epithelial cells. TLR2-driven intracellular signaling via ERK1/2, JNK and particularly NF-κB plays a role in this process. Based on these results, it is possible that expression of porin sequence variants that strongly induce TLR2 activation may be a mechanism to enhance the invasive features of pathogenic Neisseriae strains.

Typing and surface charges of the variable loop regions of PorB from Neisseria meningitidis

PorB is a pan-Neisserial major outer membrane protein with a trimeric β-barrel structure. Each monomer presents eight periplasmic turns and eight surface exposed loop regions with sequence variability. PorB induces activation of host cell responses via a TLR2-dependent mechanism likely mediated by electrostatic interactions between TLR2 and PorB surface exposed loops. Variability in the loop amino acid sequence is known to influence cell responses to PorB in vitro, particularly for the residues in L5 and L7. In this work, the sequence of the porB gene and the electrostatic surface charges of PorB from 35 invasive meningococcal isolates belonging to the main clonal complexes identified in Italy and from five carriage genomes available on the website http://pubmlst.org/neisseria/ were examined. Analysis of the porB encoding regions from the invasive meningococci has identified four new alleles and a potential association between porB alleles, serogroup, and clonal complexes. Through computer-based modeling and analysis of the electrostatic surface charges of PorB from these strains, loop charge segregation between PorB from invasive serogroups B and C was observed. Specifically, loops 1, 4, and 7 were negatively charged and L2 and L8 were mostly neutral in serogroup B isolates, while an overall homogeneous positive surface charge was present in PorB from invasive serogroup C strains. A higher PorB sequence variability was observed among carriage genomes, and a general prevalence of negative loop surface charges. The surface charge differences in PorB from serogroups B and C invasive and carriage strains may, in part, influence the outcomes of Neisseriae interactions with host cells. © 2016 IUBMB Life, 68(6):488-495, 2016.

Surface Proteoglycans as Mediators in Bacterial Pathogens Infections

Infectious diseases remain an important global health problem. The interaction of a wide range of pathogen bacteria with host cells from many different tissues is frequently mediated by proteoglycans. These compounds are ubiquitous complex molecules which are not only involved in adherence and colonization, but can also participate in other steps of pathogenesis. To overcome the problem of microbial resistance to antibiotics new therapeutic agents could be developed based on the characteristics of the interaction of pathogens with proteoglycans.

Rho GTPases as pathogen targets: Focus on curable sexually transmitted infections

Pathogens have evolved highly specialized mechanisms to infect hosts. Several microorganisms modulate the eukaryotic cell surface to facilitate their engulfment. Once internalized, they hijack the molecular machinery of the infected cell for their own benefit. At different stages of phagocytosis, particularly during invasion, certain pathogens manipulate pathways governed by small GTPases. In this review, we focus on the role of Rho proteins on curable, sexually transmitted infections caused by Chlamydia trachomatis, Neisseria gonorrhoeae, Trichomonas vaginalis and Treponema pallidum. Despite the high, worldwide frequencies of these sexually-transmitted diseases, very little is known about the strategies developed by these microorganisms to usurp key eukaryotic proteins that control intracellular signaling and actin dynamics. Improved knowledge of these molecular mechanisms will contribute to the elucidation of how these clinically important pathogens manipulate intracellular processes and parasitize their hosts.

Neutral sphingomyelinase 2 is a key factor for PorB-dependent invasion of Neisseria gonorrhoeae

Disseminated gonococcal infection (DGI) is a rare but serious complication caused by the spread of Neisseria gonorrhoeae in the human host. Gonococci associated with DGI mainly express the outer membrane protein PorBIA that binds to the scavenger receptor expressed on endothelial cells (SREC-I) and mediates bacterial uptake. We recently demonstrated that this interaction relies on intact membrane rafts that acquire SREC-I upon attachment of gonococci and initiates the signalling cascade that finally leads to the uptake of gonococci in epithelial cells. In this study, we analysed the role of sphingomyelinases and their breakdown product ceramide. Gonococcal infection induced increased levels of ceramide that was enriched at bacterial attachment sites. Interestingly, neutral but not acid sphingomyelinase was mandatory for PorBIA -mediated invasion into host cells. Neutral sphingomyelinase was required to recruit the PI3 kinase to caveolin and thereby activates the PI3 kinase-dependent downstream signalling leading to bacterial uptake. Thus, this study elucidates the initial signalling processes of bacterial invasion during DGI and demonstrates a novel role for neutral sphingomyelinase in the course of bacterial infections.

Saturating mutagenesis of an essential gene: a majority of the Neisseria gonorrhoeae major outer membrane porin (PorB) is mutable

The major outer membrane porin (PorB) of Neisseria gonorrhoeae is an essential protein that mediates ion exchange between the organism and its environment and also plays multiple roles in human host pathogenesis. To facilitate structure-function studies of porin's multiple roles, we performed saturating mutagenesis at the porB locus and used deep sequencing to identify essential versus mutable residues. Random mutations in porB were generated in a plasmid vector, and mutant gene pools were transformed into N. gonorrhoeae to select for alleles that maintained bacterial viability. Deep sequencing of the input plasmid pools and the output N. gonorrhoeae genomic DNA pools identified mutations present in each, and the mutations in both pools were compared to determine which changes could be tolerated by the organism. We examined the mutability of 328 amino acids in the mature PorB protein and found that 308 of them were likely to be mutable and that 20 amino acids were likely to be nonmutable. A subset of these predictions was validated experimentally. This approach to identifying essential amino acids in a protein of interest introduces an additional application for next-generation sequencing technology and provides a template for future studies of both porin and other essential bacterial genes.

Structure-function studies of the Neisseria gonorrhoeae major outer membrane porin

The major outer membrane porin (PorB) expressed by Neisseria gonorrhoeae plays multiple roles during infection, in addition to its function as an outer membrane pore. We have generated a panel of mutants of N. gonorrhoeae strain FA1090 expressing a variety of mutant porB genes that all function as porins. We identified multiple regions of porin that are involved in its binding to the complement regulatory factors C4b-binding protein and factor H and confirmed that the ability to bind at least one factor is required for FA1090 to survive the bactericidal effects of human serum. We tested the ability of these mutants to inhibit both apoptosis and the oxidative burst in polymorphonuclear leukocytes but were unable to identify the porin domains required for either function. This study has identified nonessential porin domains and some potentially essential portions of the protein and has further expanded our understanding of the contribution of the porin domains required for complement regulation.

Pilus phase variation switches gonococcal adherence to invasion by caveolin-1-dependent host cell signaling

Many pathogenic bacteria cause local infections but occasionally invade into the blood stream, often with fatal outcome. Very little is known about the mechanism underlying the switch from local to invasive infection. In the case of Neisseria gonorrhoeae, phase variable type 4 pili (T4P) stabilize local infection by mediating microcolony formation and inducing anti-invasive signals. Outer membrane porin PorB(IA), in contrast, is associated with disseminated infection and facilitates the efficient invasion of gonococci into host cells. Here we demonstrate that loss of pili by natural pilus phase variation is a prerequisite for the transition from local to invasive infection. Unexpectedly, both T4P-mediated inhibition of invasion and PorB(IA)-triggered invasion utilize membrane rafts and signaling pathways that depend on caveolin-1-Y14 phosphorylation (Cav1-pY14). We identified p85 regulatory subunit of PI3 kinase (PI3K) and phospholipase Cγ1 as new, exclusive and essential interaction partners for Cav1-pY14 in the course of PorBIA-induced invasion. Active PI3K induces the uptake of gonococci via a new invasion pathway involving protein kinase D1. Our data describe a novel route of bacterial entry into epithelial cells and offer the first mechanistic insight into the switch from local to invasive gonococcal infection.

Innate recognition by neutrophil granulocytes differs between Neisseria gonorrhoeae strains causing local or disseminating infections

Members of the carcinoembryonic antigen-related cell adhesion molecule (CEACAM) family serve as cellular receptors for Neisseria gonorrhoeae. More specifically, neisserial colony opacity (OpaCEA)) proteins bind to epithelial CEACAMs (CEACAM1, CEA, CEACAM6) to promote bacterial colonization of the mucosa. In contrast, recognition by CEACAM3, expressed by human granulocytes, results in uptake and destruction of Opa(CEA)-expressing bacteria. Therefore, CEACAM3-mediated uptake might limit the spread of gonococci. However, some strains can cause disseminating gonococcal infections (DGIs), and it is currently unknown how these strains escape detection by granulocyte CEACAM3. Therefore, the opa gene loci from N. gonorrhoeae strain VP1, which was derived from a patient with disseminated gonococcal disease, were cloned and constitutively expressed in Escherichia coli. Similar to Opa proteins of the nondisseminating strain MS11, the majority of Opa proteins from strain VP1 bound epithelial CEACAMs and promoted CEACAM-initiated responses by epithelial cells. In sharp contrast to the Opa proteins of strain MS11, the Opa proteins of strain VP1 failed to interact with the human granulocyte receptor CEACAM3. Accordingly, bacteria expressing VP1 Opa proteins were not taken up by primary human granulocytes and did not trigger a strong oxidative burst. Analysis of Opa variants from four additional clinical DGI isolates again demonstrated a lack of CEACAM3 binding. In summary, our results reveal that particular N. gonorrhoeae strains express an Opa protein repertoire allowing engagement of epithelial CEACAMs for successful mucosal colonization, while avoiding recognition and elimination via CEACAM3-mediated phagocytosis. A failure of CEACAM3-mediated innate immune detection might be linked to the ability of gonococci to cause disseminated infections.

Structure and function of the PorB porin from disseminating Neisseria gonorrhoeae

The outer membrane of Gram-negative bacteria contains a large number of channel-forming proteins, porins, for the uptake of small nutrient molecules. Neisseria gonorrhoeae PorBIA (PorB of serotype A) are associated with disseminating diseases and mediate a rapid bacterial invasion into host cells in a phosphate-sensitive manner. To gain insights into this structure-function relationship we analysed PorBIA by X-ray crystallography in the presence of phosphate and ATP. The structure of PorBIA in the complex solved at a resolution of 3.3 Å (1 Å=0.1 nm) displays a surplus of positive charges inside the channel. ATP ligand-binding in the channel is co-ordinated by the positively charged residues of the channel interior. These residues ligate the aromatic, sugar and pyrophosphate moieties of the ligand. Two phosphate ions were observed in the structure, one of which clamped by two arginine residues (Arg92 and Arg124) localized at the extraplasmic channel exit. A short β-bulge in β2-strand together with the long L3 loop narrow the barrel diameter significantly and further support substrate specificity through hydrogen bond interactions. Interestingly the structure also comprised a small peptide as a remnant of a periplasmic protein which physically links porin molecules to the peptidoglycan network. To test the importance of Arg92 on bacterial invasion the residue was mutated. In vivo assays of bacteria carrying a R92S mutation confirmed the importance of this residue for host-cell invasion. Furthermore systematic sequence and structure comparisons of PorBIA from Neisseriaceae indicated Arg92 to be unique in disseminating N. gonorrhoeae thereby possibly distinguishing invasion-promoting porins from other neisserial porins.

Estradiol-Treated Female Mice as Surrogate Hosts for Neisseria gonorrhoeae Genital Tract Infections

Historically, animal modeling of gonorrhea has been hampered by the exclusive adaptation of Neisseria gonorrhoeae to humans. Genital tract infection can be established in female mice that are treated with 17β-estradiol, however, and many features of experimental murine infection mimic human infection. Here we review the colonization kinetics and host response to experimental murine gonococcal infection, including mouse strain differences and evidence that IL-17 responses, toll-like receptor 4, and T regulatory cells play a role in infection. We also discuss the strengths and limitations of the mouse system and the potential of transgenic mice to circumvent host restrictions. Additionally, we review studies with genetically defined mutants that demonstrated a role for sialyltransferase and the MtrC-MtrD-MtrE active efflux pump in evading innate defenses in vivo, but not for factors hypothesized to protect against the phagocytic respiratory burst and H(2)O(2)-producing lactobacilli. Studies using estradiol-treated mice have also revealed the existence of non-host-restricted iron sources in the female genital tract and the influence of hormonal factors on colonization kinetics and selection for opacity (Opa) protein expression. Recent work by others with estradiol-treated mice that are transgenic for human carcinoembryonic adhesion molecules (CEACAMs) supports a role for Opa proteins in enhancing cellular attachment and thus reduced shedding of N. gonorrhoeae. Finally we discuss the use of the mouse model in product testing and a recently developed gonorrhea chlamydia coinfection model.

The Pathobiology of Neisseria gonorrhoeae Lower Female Genital Tract Infection

Infection and disease associated with Neisseria gonorrhoeae, the gonococcus, continue to be a global health problem. Asymptomatic and subclinical gonococcal infections occur at a high frequency in females; thus, the true incidence of N. gonorrhoeae infections are presumed to be severely underestimated. Inherent to this asymptomatic/subclinical diseased state is the continued prevalence of this organism within the general population, as well as the medical, economic, and social burden equated with the observed chronic, disease sequelae. As infections of the lower female genital tract (i.e., the uterine cervix) commonly result in subclinical disease, it follows that the pathobiology of cervical gonorrhea would differ from that observed for other sites of infection. In this regard, the potential responses to infection that are generated by the female reproductive tract mucosa are unique in that they are governed, in part, by cyclic fluctuations in steroid hormone levels. The lower female genital tract has the further distinction of being able to functionally discriminate between resident commensal microbiota and transient pathogens. The expression of functionally active complement receptor 3 by the lower, but not the upper, female genital tract mucosa; together with data indicating that gonococcal adherence to and invasion of primary cervical epithelial cells and tissue are predominately aided by this surface-expressed host molecule; provide one explanation for asymptomatic/subclinical gonococcal cervicitis. However, co-evolution of the gonococcus with its sole human host has endowed this organism with variable survival strategies that not only aid these bacteria in successfully evasion of immune detection and function but also enhance cervical colonization and cellular invasion. To this end, we herein summarize current knowledge pertaining to the pathobiology of gonococcal infection of the human cervix.

Predominant porB1A and porB1B genotypes and correlation of gene mutations with drug resistance in Neisseria gonorrhoeae isolates in Eastern China

BACKGROUND

Variations of porB1A and porB1B genes and their serotypes exist in Neisseria gonorrhoeae isolates from different geographical areas, and some site mutations in the porB1B gene correlate with drug resistance.

METHODS

The β-lactamase production of N. gonorrhoeae isolates was determined by paper acidometric test and nitrocefin discs. The porB1A and porB1B genes of 315 non-penicillinase-producting N. gonorrhoeae (non-PPNG) strains were amplified by PCR for sequencing to determine serotypes and site mutations. A duplex PCR was designed to simultaneously detect both porB1A and porB1B genes. Penicillin and tetracycline resistance was assessed by an in vitro drug sensitivity test.

RESULTS

Of the N. gonorrhoeae isolates, 31.1% tested positive for porB1A and 68.9% for porB1B genes. All the 98 porB1A+ isolates belonging to IA6 serotype with either no mutation at the 120 and 121 sites (88.8%) or a D120G (11.2%) mutation and were no resistance to both penicillin and tetracycline. Among the 217 porB1B+ isolates, 26.7%, 22.6% and 11.5% belonged to IB3, IB3/6 and IB4 serotypes, respectively. Particularly, two novel chimeric serotypes, IB3/6-IB2 and IB2-IB4-IB2, were found in 77 and 8 porB1B+ isolates. Two hundred and twelve (97.7%) of the porB1B+ isolates were presented G120 and/or A121 mutations with 163 (76.9%) at both sites. Interestingly, within the 77 porB1B+ isolates belonging to IB3/6-IB2 serotype, 15 were discovered to possess novel deletions at both A121 and N122 sites. All the replacement mutations at these sites in PorB1B were correlated with resistance and the deletion mutation showed the highest resistance.

CONCLUSION

N. gonorrhoeae isolates circulating in Eastern China include a sole PorB1A serotype (IA6) and five PorB1B serotypes. Multiple mutations in porB1B genes, including novel A121 and N122 deletions, are correlated with high levels of penicillin and tetracycline resistance.

Meningococcal internalization into human endothelial and epithelial cells is triggered by the influx of extracellular L-glutamate via GltT L-glutamate ABC transporter in Neisseria meningitidis

Meningococcal internalization into human cells is likely to be a consequence of meningococcal adhesion to human epithelial and endothelial cells. Here, we identified three transposon mutants of Neisseria meningitidis that were primarily defective in the internalization of human brain microvascular endothelial cells (HBMEC), with insertions occurring in the gltT (a sodium-independent L-glutamate transporter) gene or its neighboring gene, NMB1964 (unknown function). NMB1964 was tentatively named gltM in this study because of the presence of a mammalian cell entry (MCE)-related domain in the deduced amino acid sequences. The null ΔgltT-ΔgltM N. meningitidis mutant was also defective in the internalization into human umbilical vein endothelial cells and the human lung carcinoma epithelial cell line A549, and the defect was suppressed by transcomplementation of the mutants with gltT(+)-gltM(+) genes. The intracellular survival of the ΔgltT-ΔgltM mutant in HBMEC was not largely different from that of the wild-type strain under our experimental conditions. Introduction of a1-bp deletion and amber or ochre mutations in gltT-gltM genes resulted in the loss of efficient internalization into HBMEC. The defect in meningococcal internalization into HBMEC and L-glutamate uptake in the ΔgltT-ΔgltM mutant were suppressed only in strains expressing both GltT and GltM proteins. The efficiency of meningococcal invasion to HBMEC decreased under L-glutamate-depleted conditions. Furthermore, ezrin, a key membrane-cytoskeleton linker, accumulated beneath colonies of the gltT(+)-gltM(+) N. meningitidis strain but not of the ΔgltT-ΔgltM mutant. These findings suggest that l-glutamate influx via the GltT-GltM L-glutamate ABC transporter serves as a cue for N. meningitidis internalization into host cells.