Neisseria gonorrhoeae elicits membrane ruffling and cytoskeletal rearrangements upon infection of primary human endocervical and ectocervical cells

Neisseria gonorrhoeae antimicrobial resistance patterns and associated risk factors in women of childbearing potential in northwestern Ethiopia

BACKGROUNDS

Neisseria gonorrhoeae causes gonorrhea and poses public health problems, including antimicrobial resistance. Current data on gonorrhea in prenatal participants in the study area are required. Thus, we aimed to identify gonorrhea prevalence, antimicrobial resistance, and risk factors among antenatal care clinic visitors in northwestern Ethiopia.

METHODS

A cross-sectional study was conducted from March to August 2022 at the University of Gondar Comprehensive Specialized Hospital. We recruited 278 study participants using convenient sampling techniques. Sociodemographic, clinical and behavioral risk factors were recorded using pre-tested questionnaires. Endocervical swabs were collected by a physician, transported to the microbiology laboratory, immediately inoculated into modified Thayer-Martin medium, and it was incubated at 37 °C for 24-48 hours. Gram staining and biochemical tests were used to identify the organism. AMR testing was performed using disc diffusion and E-test methods. Data were entered in EPI-info version 7 and exported and analyzed in SPSS version 26. A p-value ≤0.05 was considered as statistically significant. Results were presented in words, tables and figure.

RESULTS

Of 278 subjects enrolled, majority (44.6%) were 26-35 years, with a mean age of 29.9 (SD = ±7.2) years, 69.4% were urban residents, and 70.5% were married. Twenty-one (7.6%) participants had gonorrhea. Overall antimicrobial resistance ranged from 19 to 100%. High resistant to tetracycline (100%) and penicillin (85.7%) were observed by both tests. Ciprofloxacin resistance was 52.4% by disc diffusion and 85.7% by E-test. By E-test, all isolates were sensitive to ceftriaxone, cefixime, azithromycin and spectinomycin; however, 7 (33.3%), 9 (42.9%), 9 (42.9%) and 5 (23.8%) isolates showed resistant to these antibiotics with disk method. Prevalence of beta-lactamase producing Neisseria gonorrhoeae was 85.7%. Alcohol consumption (p = 0.032), condom-free sexual practice (p = 0.010), multiple sexual partners (p < 0.001), pelvic pain (p = 0.018), and dysuria (p = 0.021) revealed increased risk of infection.

CONCLUSIONS

Compared with many previous studies in Ethiopia, we found high prevalence, antimicrobial resistance, and beta-lactamase-positive isolates. Multiple sexual partners, alcohol consumption, not using condom, pelvic pain and dysuria were predictors of this infection. Continuous large-scale monitoring of pathogen is essential for its prevention and control.

A Review of Recent Advances in Our Understanding of Neisseria gonorrhoeae

Gonorrhoea is an infection caused by bacteria that has recently been detected in humans and typically spreads through sexual contact. It leads to significant health issues in both prosperous and impoverished countries, culminating in significant yearly expenditures for diagnosis and treatment. Young adults who are involved in unprotected sexual activity and are promiscuous are particularly susceptible to gonorrhoea. It has been estimated that approximately 86.95 million individuals globally acquire the virus each year. Gonorrhoea has been reported to affect a variety of body parts, including the cervix in women and the urethra in males, as well as other areas such as the eyes, anus, throat, and, on rare occasions, the joints. It is momentarily the second most frequently reported sexually transmitted disease (STD) by the Centers for Disease Control and Prevention (CDC), trailing only chlamydia. Since the early 2000s, gonorrhoea cases have been on the rise globally, especially across many European nations, with an elevated prevalence among populations at higher risk of getting sexually transmitted infections (STIs), such as men who have sex with men and young heterosexual individuals. The fundamental objectives of gonorrhoea management techniques are to prevent, identify, and cure infections in patients and their partners in addition to minimizing the disease's stigma. It additionally involves monitoring antibiotic resistance and treatment failures, and it also involves advocating appropriate antimicrobial medication usage and stewardship.

Mechanisms of host manipulation by Neisseria gonorrhoeae

Neisseria gonorrhoeae (also known as gonococcus) has been causing gonorrhoea in humans since ancient Egyptian times. Today, global gonorrhoea infections are rising at an alarming rate, in concert with an increasing number of antimicrobial-resistant strains. The gonococcus has concurrently evolved several intricate mechanisms that promote pathogenesis by evading both host immunity and defeating common therapeutic interventions. Central to these adaptations is the ability of the gonococcus to manipulate various host microenvironments upon infection. For example, the gonococcus can survive within neutrophils through direct regulation of both the oxidative burst response and maturation of the phagosome; a concerning trait given the important role neutrophils have in defending against invading pathogens. Hence, a detailed understanding of how N. gonorrhoeae exploits the human host to establish and maintain infection is crucial for combating this pathogen. This review summarizes the mechanisms behind host manipulation, with a central focus on the exploitation of host epithelial cell signaling to promote colonization and invasion of the epithelial lining, the modulation of the host immune response to evade both innate and adaptive defenses, and the manipulation of host cell death pathways to both assist colonization and combat antimicrobial activities of innate immune cells. Collectively, these pathways act in concert to enable N. gonorrhoeae to colonize and invade a wide array of host tissues, both establishing and disseminating gonococcal infection.

Repurposing Carbamazepine To Treat Gonococcal Infection in Women: Oral Delivery for Control of Epilepsy Generates Therapeutically Effective Levels in Vaginal Secretions

Neisseria gonorrhoeae has developed resistance to all previous antibiotics used for treatment. This highlights a crucial need for novel antimicrobials to treat gonococcal infections. We previously showed that carbamazepine (Cz), one of the most commonly prescribed antiepileptic drugs, can block the interaction between gonococcal pili and the I-domain region of human complement receptor 3 (CR3)-an interaction that is vital for infection of the female cervix. We also show that Cz can completely clear an established N. gonorrhoeae infection of primary human cervical cells. In this study, we quantified Cz in serum, saliva, and vaginal fluid collected from 16 women who were, or were not, regularly taking Cz. We detected Cz in lower reproductive tract mucosal secretions in the test group (women taking Cz) at potentially therapeutic levels using a competitive ELISA. Furthermore, we found that Cz concentrations present in vaginal fluid from women taking this drug were sufficient to result in a greater than 99% reduction (within 24 h) in the number of viable gonococci recovered from ex vivo, human, primary cervical cell infections. These data provide strong support for the further development of Cz as a novel, host-targeted therapy to treat gonococcal cervicitis.

Potent In Vitro and Ex Vivo Anti-Gonococcal Activity of the RpoB Inhibitor Corallopyronin A

Gonorrhea remains a major global public health problem because of the high incidence of infection (estimated 82 million cases in 2020) and the emergence and spread of Neisseria gonorrhoeae strains resistant to previous and current antibiotics used to treat infections. Given the dearth of new antibiotics that are likely to enter clinical practice in the near future, there is concern that cases of untreatable gonorrhea might emerge. In response to this crisis, the World Health Organization (WHO), in partnership with the Global Antibiotic Research and Development Partnership (GARDP), has made the search for and development of new antibiotics against N. gonorrhoeae a priority. Ideally, these antibiotics should also be active against other sexually transmitted organisms, such as Chlamydia trachomatis and/or Mycoplasma genitalium, which are often found with N. gonorrhoeae as co-infections. Corallopyronin A is a potent antimicrobial that exhibits activity against Chlamydia spp. and inhibits transcription by binding to the RpoB switch region. Accordingly, we tested the effectiveness of corallopyronin A against N. gonorrhoeae. We also examined the mutation frequency and modes of potential resistance against corallopyronin A. We report that corallopyronin A has potent antimicrobial action against antibiotic-susceptible and antibiotic-resistant N. gonorrhoeae strains and could eradicate gonococcal infection of cultured, primary human cervical epithelial cells. Critically, we found that spontaneous corallopyronin A-resistant mutants of N. gonorrhoeae are exceedingly rare (≤10^-10) when selected at 4× the MIC. Our results support pre-clinical studies aimed at developing corallopyronin A for gonorrheal treatment regimens. IMPORTANCE The high global incidence of gonorrhea, the lack of a protective vaccine, and the emergence of N. gonorrhoeae strains expressing resistance to currently used antibiotics demand that new treatment options be developed. Accordingly, we investigated whether corallopyronin A, an antibiotic which is effective against other pathogens, including C. trachomatis, which together with gonococci frequently cause co-infections in humans, could exert anti-gonococcal action in vitro and ex vivo, and potential resistance emergence. We propose that corallopyronin A be considered a potential future treatment option for gonorrhea because of its potent activity, low resistance development, and recent advances in scalable production.

Complement Receptor 3 Mediates HIV-1 Transcytosis across an Intact Cervical Epithelial Cell Barrier: New Insight into HIV Transmission in Women

Transmission of HIV across the mucosal surface of the female reproductive tract to engage subepithelial CD4-positive T cells is not fully understood. Cervical epithelial cells express complement receptor 3 (CR3) (integrin αMβ2 or CD11b/CD18). In women, the bacterium Neisseria gonorrhoeae uses CR3 to invade the cervical epithelia to cause cervicitis. We hypothesized that HIV may also use CR3 to transcytose across the cervical epithelia. Here, we show that HIV-1 strains bound with high affinity to recombinant CR3 in biophysical assays. HIV-1 bound CR3 via the I-domain region of the CR3 alpha subunit, CD11b, and binding was dependent on HIV-1 N-linked glycans. Mannosylated glycans on the HIV surface were a high-affinity ligand for the I-domain. Man5 pentasaccharide, representative of HIV N-glycans, could compete with HIV-1 for CR3 binding. Using cellular assays, we show that HIV bound to CHO cells by a CR3-dependent mechanism. Antibodies to the CR3 I-domain or to the HIV-1 envelope glycoprotein blocked the binding of HIV-1 to primary human cervical epithelial (Pex) cells, indicating that CR3 was necessary and sufficient for HIV-1 adherence to Pex cells. Using Pex cells in a Transwell model system, we show that, following transcytosis across an intact Pex cell monolayer, HIV-1 is able to infect TZM-bl reporter cells. Targeting the HIV-CR3 interaction using antibodies, mannose-binding lectins, or CR3-binding small-molecule drugs blocked HIV transcytosis. These studies indicate that CR3/Pex may constitute an efficient pathway for HIV-1 transmission in women and also demonstrate strategies that may prevent transmission via this pathway. IMPORTANCE In women, the lower female reproductive tract is the primary site for HIV infection. How HIV traverses the epithelium to infect CD4 T cells in the submucosa is ill-defined. Cervical epithelial cells have a protein called CR3 on their surface. We show that HIV-1 binds to CR3 with high affinity and that this interaction is necessary and sufficient for HIV adherence to, and transcytosis across, polarized, human primary cervical epithelial cells. This suggests a unique role for CR3 on epithelial cells in dually facilitating HIV-1 attachment and entry. The HIV-CR3 interaction may constitute an efficient pathway for HIV delivery to subepithelial lymphocytes following virus transmission across an intact cervical epithelial barrier. Strategies with potential to prevent transmission via this pathway are presented.

Neisseria gonorrhoeae physiology and pathogenesis

Neisseria gonorrhoeae is an obligate human pathogen that is the cause of the sexually transmitted disease gonorrhoea. Recently, there has been a surge in gonorrhoea cases that has been exacerbated by the rapid rise in gonococcal multidrug resistance to all useful antimicrobials resulting in this organism becoming a significant public health burden. Therefore, there is a clear and present need to understand the organism's biology through its physiology and pathogenesis to help develop new intervention strategies. The gonococcus initially colonises and adheres to host mucosal surfaces utilising a type IV pilus that helps with microcolony formation. Other adhesion strategies include the porin, PorB, and the phase variable outer membrane protein Opa. The gonococcus is able to subvert complement mediated killing and opsonisation by sialylation of its lipooligosaccharide and deploys a series of anti-phagocytic mechanisms. N. gonorrhoeae is a fastidious organism that is able to grow on a limited number of primary carbon sources such as glucose and lactate. The utilization of lactate by the gonococcus has been implicated in a number of pathogenicity mechanisms. The bacterium lives mainly in microaerobic environments and can grow both aerobically and anaerobically with the aid of nitrite. The gonococcus does not produce siderophores for scavenging iron but can utilize some produced by other bacteria, and it is able to successful chelate iron from host haem, transferrin and lactoferrin. The gonococcus is an incredibly versatile human pathogen; in the following chapter, we detail the intricate mechanisms used by the bacterium to invade and survive within the host.

Tissue Models for Neisseria gonorrhoeae Research—From 2D to 3D

Neisseria gonorrhoeae is a human-specific pathogen that causes gonorrhea, the second most common sexually transmitted infection worldwide. Disease progression, drug discovery, and basic host-pathogen interactions are studied using different approaches, which rely on models ranging from 2D cell culture to complex 3D tissues and animals. In this review, we discuss the models used in N. gonorrhoeae research. We address both in vivo (animal) and in vitro cell culture models, discussing the pros and cons of each and outlining the recent advancements in the field of three-dimensional tissue models. From simple 2D monoculture to complex advanced 3D tissue models, we provide an overview of the relevant methodology and its application. Finally, we discuss future directions in the exciting field of 3D tissue models and how they can be applied for studying the interaction of N. gonorrhoeae with host cells under conditions closely resembling those found at the native sites of infection.

Gonococcal invasion into epithelial cells depends on both cell polarity and ezrin

Neisseria gonorrhoeae (GC) establishes infection in women from the cervix, lined with heterogeneous epithelial cells from non-polarized stratified at the ectocervix to polarized columnar at the endocervix. We have previously shown that GC differentially colonize and transmigrate across the ecto and endocervical epithelia. However, whether and how GC invade into heterogeneous cervical epithelial cells is unknown. This study examined GC entry of epithelial cells with various properties, using human cervical tissue explant and non-polarized/polarized epithelial cell line models. While adhering to non-polarized and polarized epithelial cells at similar levels, GC invaded into non-polarized more efficiently than polarized epithelial cells. The enhanced GC invasion in non-polarized epithelial cells was associated with increased ezrin phosphorylation, F-actin and ezrin recruitment to GC adherent sites, and the elongation of GC-associated microvilli. Inhibition of ezrin phosphorylation inhibited F-actin and ezrin recruitment and microvilli elongation, leading to a reduction in GC invasion. The reduced GC invasion in polarized epithelial cells was associated with non-muscle myosin II-mediated F-actin disassembly and microvilli denudation at GC adherence sites. Surprisingly, intraepithelial GC were only detected inside epithelial cells shedding from the cervix by immunofluorescence microscopy, but not significantly in the ectocervical and the endocervical regions. We observed similar ezrin and F-actin recruitment in exfoliated cervical epithelial cells but not in those that remained in the ectocervical epithelium, as the luminal layer of ectocervical epithelial cells expressed ten-fold lower levels of ezrin than those beneath. However, GC inoculation induced F-actin reduction and myosin recruitment in the endocervix, similar to what was seen in polarized epithelial cells. Collectively, our results suggest that while GC invade non-polarized epithelial cells through ezrin-driven microvilli elongation, the apical polarization of ezrin and F-actin inhibits GC entry into polarized epithelial cells.

Neisseria gonorrhoeae (GC) causes gonorrhea in women by infecting the female reproductive tract. GC entry of epithelial cells has long been observed in patients’ biopsies and studied in various types of epithelial cells. However, how GC invade into the heterogeneous epithelia of the human cervix is unknown. This study reveals that both the expression level of ezrin, an actin-membrane linker protein, and the polarization of ezrin-actin networks in epithelial cells regulate GC invasion. GC interactions with non-polarized squamous epithelial cells expressing ezrin induce ezrin activation, ezrin-actin accumulation, and microvilli elongation at GC adherent sites, leading to invasion. Low ezrin expression levels in the luminal ectocervical epithelial cells are associated with low levels of intraepithelial GC. In contrast, apical polarization of ezrin-actin networks in columnar endocervical epithelial cells reduces GC invasion. GC interactions induce myosin activation, which causes disassembly of ezrin-actin networks and microvilli modification at GC adherent sites, extending GC-epithelial contact. Expression of opacity-associated proteins on GC promotes GC invasion by enhancing ezrin-actin accumulation in squamous epithelial cells and inhibiting ezrin-actin disassembly in columnar endocervical epithelial cells. Thus, reduced ezrin expression and ezrin-actin polarization are potential ways for cervical epithelial cells to curtail GC invasion.

A drug candidate for Alzheimer's and Huntington's disease, PBT2, can be repurposed to render Neisseria gonorrhoeae susceptible to natural cationic antimicrobial peptides

BACKGROUND

Neisseria gonorrhoeae is a Gram-negative bacterial pathogen that causes gonorrhoea. No vaccine is available to prevent gonorrhoea and the emergence of MDR N. gonorrhoeae strains represents an immediate public health threat.

OBJECTIVES

To evaluate whether PBT2/zinc may sensitize MDR N. gonorrhoeae to natural cationic antimicrobial peptides.

METHODS

MDR strains that contain differing resistance mechanisms against numerous antibiotics were tested in MIC assays. MIC assays were performed using the broth microdilution method according to CLSI guidelines in a microtitre plate. Serially diluted LL-37 or PG-1 was tested in combination with a sub-inhibitory concentration of PBT2/zinc. Serially diluted tetracycline was also tested with sub-inhibitory concentrations of PBT2/zinc and LL-37. SWATH-MS proteomic analysis of N. gonorrhoeae treated with PBT2/zinc, LL-37 and/or tetracycline was performed to determine the mechanism(s) of N. gonorrhoeae susceptibility to antibiotics and peptides.

RESULTS

Sub-inhibitory concentrations of LL-37 and PBT2/zinc synergized to render strain WHO-Z susceptible to tetracycline, whereas the killing effect of PG-1 and PBT2/zinc was additive. SWATH-MS proteomic analysis suggested that PBT2/zinc most likely leads to a loss of membrane integrity and increased protein misfolding and, in turn, results in bacterial death.

CONCLUSIONS

Here we show that PBT2, a candidate Alzheimer's and Huntington's disease drug, can be repurposed to render MDR N. gonorrhoeae more susceptible to the endogenous antimicrobial peptides LL-37 and PG-1. In the presence of LL-37, PBT2/zinc can synergize with tetracycline to restore tetracycline susceptibility to gonococci resistant to this antibiotic.

Complement receptor 3 mediates ruffle-like, actin-rich aggregates during phagocytosis of Leishmania infantum metacyclics

The parasitic protozoan Leishmania infantum resides primarily in macrophages throughout mammalian infection. Infection is initiated by deposition of the metacyclic promastigote into the dermis of a mammalian host by the sand fly vector. Promastigotes enter macrophages by ligating surface receptors such as complement receptor 3 (CR3), inducing phagocytosis of the parasite. At the binding site of metacyclic promastigotes, we observed large asymmetrical aggregates of macrophage membrane with underlying actin, resembling membrane ruffles. Actin accumulation was observed at the point of initial contact, before phagosome formation and accumulation of peri-phagosomal actin. Ruffle-like structures did not form during phagocytosis of attenuated promastigotes or during phagocytosis of the intracellular amastigote form of L. infantum. Entry of promastigotes through massive actin accumulation was associated with a subsequent delay in fusion of the parasitophorous vacuole (PV) with the lysosomal markers LAMP-1 and Cathepsin D. Actin accumulation was also associated with entry through CR3, since macrophages from CD11b knockout (KO) mice did not form massive aggregates of actin during phagocytosis of metacyclic promastigotes. Furthermore, intracellular survival of L. infantum was significantly decreased in CD11b KO compared to wild type macrophages, although entry rates were similar. We conclude that both promastigote virulence and host cell CR3 are needed for the formation of ruffle-like membrane structures at the site of metacyclic promastigote phagocytosis, and that formation of actin-rich aggregates during entry correlates with the intracellular survival of virulent promastigotes.

Repurposing Fenamic Acid Drugs To Combat Multidrug-Resistant Neisseria gonorrhoeae

The rise of extensively drug-resistant and multidrug-resistant strains of Neisseria gonorrhoeae has occurred in parallel with the increasing demand for new drugs. However, the current methods of drug discovery are burdened with rigorous assessments and require more time than can be spared until gonococcal infections become difficult to control. To address this urgency, we utilized a drug-repurposing strategy and identified three clinically approved anthranilic acid drugs (tolfenamic acid, flufenamic acid, and meclofenamic acid) with potent antigonococcal activity, inhibiting 50% of the strains (MIC₅₀) from 4 to 16 μg/ml. Furthermore, tolfenamic acid showed indifferent activity with antibiotics of choice for gonococcal infections, azithromycin and ceftriaxone, in checkerboard assays with a fractional inhibitory concentration index ranging from 0.75 to 1.5. Fenamic acids reduced a high inoculum of N. gonorrhoeae below the limit of detection within 12 h and exhibited a low frequency of resistance. Interestingly, the fenamic acids did not inhibit the growth of commensal Lactobacillus spp. that comprise the healthy female genital microbiota. Fenamic acids were also superior to ceftriaxone in reducing the burden of intracellular N. gonorrhoeae within infected endocervical cells by 99%. Furthermore, all three fenamic acids significantly reduced the expression of proinflammatory cytokines by infected endocervical cells. Finally, fenamic acids and other structurally related anthranilic acid derivatives were evaluated to ascertain a more in-depth structure-activity relationship (SAR) that revealed N-phenylanthranilic acid as a novel antigonorrheal scaffold. This SAR study will pave the road to repositioning more potent fenamic acids analogues against N. gonorrhoeae.

Repurposed Drugs That Block the Gonococcus-Complement Receptor 3 Interaction Can Prevent and Cure Gonococcal Infection of Primary Human Cervical Epithelial Cells

Novel therapies that avert the problem of Neisseria gonorrhoeae with acquired antibiotic resistance are urgently needed. Gonococcal infection of the human cervix is initiated by an interaction between a galactose modification made to its surface appendages, pili, and the I-domain region of (host) complement receptor 3 (CR3). By targeting this crucial gonococcal–I-domain interaction, it may be possible to prevent cervical infection in females. To this end, we identified the I-domain galactose-binding epitope of CR3 and characterized its galactose lectin activity. Moreover, we identified two drugs, carbamazepine and methyldopa, as effective host-targeted therapies for gonorrhea treatment. At doses below those currently used for their respective existing indications, both carbamazepine and methyldopa were more effective than ceftriaxone in curing cervical infection ex vivo. This host-targeted approach would not be subject to N. gonorrhoeae drug resistance mechanisms. Thus, our data suggest a long-term solution to the growing problem of multidrug-resistant N. gonorrhoeae infections.

In the absence of a vaccine, multidrug-resistant Neisseria gonorrhoeae has emerged as a major human health threat, and new approaches to treat gonorrhea are urgently needed. N. gonorrhoeae pili are posttranslationally modified by a glycan that terminates in a galactose. The terminal galactose is critical for initial contact with the human cervical mucosa via an interaction with the I-domain of complement receptor 3 (CR3). We have now identified the I-domain galactose-binding epitope and characterized its galactose-specific lectin activity. Using surface plasmon resonance and cellular infection assays, we found that a peptide mimic of this galactose-binding region competitively inhibited the N. gonorrhoeae-CR3 interaction. A compound library was screened for potential drugs that could similarly prohibit the N. gonorrhoeae-CR3 interaction and be repurposed as novel host-targeted therapeutics for multidrug-resistant gonococcal infections in women. Two drugs, methyldopa and carbamazepine, prevented and cured cervical cell infection by multidrug-resistant gonococci by blocking the gonococcal-CR3 I-domain interaction.

Gonorrhoea

The bacterium Neisseria gonorrhoeae causes the sexually transmitted infection (STI) gonorrhoea, which has an estimated global annual incidence of 86.9 million adults. Gonorrhoea can present as urethritis in men, cervicitis or urethritis in women, and in extragenital sites (pharynx, rectum, conjunctiva and, rarely, systemically) in both sexes. Confirmation of diagnosis requires microscopy of Gram-stained samples, bacterial culture or nucleic acid amplification tests. As no gonococcal vaccine is available, prevention relies on promoting safe sexual behaviours and reducing STI-associated stigma, which hinders timely diagnosis and treatment thereby increasing transmission. Single-dose systemic therapy (usually injectable ceftriaxone plus oral azithromycin) is the recommended first-line treatment. However, a major public health concern globally is that N. gonorrhoeae is evolving high levels of antimicrobial resistance (AMR), which threatens the effectiveness of the available gonorrhoea treatments. Improved global surveillance of the emergence, evolution, fitness, and geographical and temporal spread of AMR in N. gonorrhoeae, and improved understanding of the pharmacokinetics and pharmacodynamics for current and future antimicrobials in the treatment of urogenital and extragenital gonorrhoea, are essential to inform treatment guidelines. Key priorities for gonorrhoea control include strengthening prevention, early diagnosis, and treatment of patients and their partners; decreasing stigma; expanding surveillance of AMR and treatment failures; and promoting responsible antimicrobial use and stewardship. To achieve these goals, the development of rapid and affordable point-of-care diagnostic tests that can simultaneously detect AMR, novel therapeutic antimicrobials and gonococcal vaccine(s) in particular is crucial.

Pathogenesis of Neisseria gonorrhoeae and the Host Defense in Ascending Infections of Human Fallopian Tube

Neisseria gonorrhoeae is an obligate human pathogen that causes mucosal surface infections of male and female reproductive tracts, pharynx, rectum, and conjunctiva. Asymptomatic or unnoticed infections in the lower reproductive tract of women can lead to serious, long-term consequences if these infections ascend into the fallopian tube. The damage caused by gonococcal infection and the subsequent inflammatory response produce the condition known as pelvic inflammatory disease (PID). Infection can lead to tubal scarring, occlusion of the oviduct, and loss of critical ciliated cells. Consequences of the damage sustained on the fallopian tube epithelium include increased risk of ectopic pregnancy and tubal-factor infertility. Additionally, the resolution of infection can produce new adhesions between internal tissues, which can tear and reform, producing chronic pelvic pain. As a bacterium adapted to life in a human host, the gonococcus presents a challenge to the development of model systems for probing host-microbe interactions. Advances in small-animal models have yielded previously unattainable data on systemic immune responses, but the specificity of N. gonorrhoeae for many known (and unknown) host targets remains a constant hurdle. Infections of human volunteers are possible, though they present ethical and logistical challenges, and are necessarily limited to males due to the risk of severe complications in women. It is routine, however, that normal, healthy fallopian tubes are removed in the course of different gynecological surgeries (namely hysterectomy), making the very tissue most consequentially damaged during ascending gonococcal infection available for laboratory research. The study of fallopian tube organ cultures has allowed the opportunity to observe gonococcal biology and immune responses in a complex, multi-layered tissue from a natural host. Forty-five years since the first published example of human fallopian tube being infected ex vivo with N. gonorrhoeae, we review what modeling infections in human tissue explants has taught us about the gonococcus, what we have learned about the defenses mounted by the human host in the upper female reproductive tract, what other fields have taught us about ciliated and non-ciliated cell development, and ultimately offer suggestions regarding the next generation of model systems to help expand our ability to study gonococcal pathogenesis.

Pili mediated intercellular forces shape heterogeneous bacterial microcolonies prior to multicellular differentiation

Microcolonies are aggregates of a few dozen to a few thousand cells exhibited by many bacteria. The formation of microcolonies is a crucial step towards the formation of more mature bacterial communities known as biofilms, but also marks a significant change in bacterial physiology. Within a microcolony, bacteria forgo a single cell lifestyle for a communal lifestyle hallmarked by high cell density and physical interactions between cells potentially altering their behaviour. It is thus crucial to understand how initially identical single cells start to behave differently while assembling in these tight communities. Here we show that cells in the microcolonies formed by the human pathogen Neisseria gonorrhoeae (Ng) present differential motility behaviors within an hour upon colony formation. Observation of merging microcolonies and tracking of single cells within microcolonies reveal a heterogeneous motility behavior: cells close to the surface of the microcolony exhibit a much higher motility compared to cells towards the center. Numerical simulations of a biophysical model for the microcolonies at the single cell level suggest that the emergence of differential behavior within a multicellular microcolony of otherwise identical cells is of mechanical origin. It could suggest a route toward further bacterial differentiation and ultimately mature biofilms.

Bilayer Properties of Lipid A from Various Gram-Negative Bacteria

Lipid A is the lipid anchor of a lipopolysaccharide in the outer leaflet of the outer membrane of Gram-negative bacteria. In general, lipid A consists of two phosphorylated N-acetyl glucosamine and several acyl chains that are directly linked to the two sugars. Depending on the bacterial species and environments, the acyl chain number and length vary, and lipid A can be chemically modified with phosphoethanolamine, aminoarabinose, or glycine residues, which are key to bacterial pathogenesis. In this work, homogeneous lipid bilayers of 21 distinct lipid A types from 12 bacterial species are modeled and simulated to investigate the differences and similarities of their membrane properties. In addition, different neutralizing ion types (Ca²⁺, K⁺, and Na⁺) are considered to examine the ion's influence on the membrane properties. The trajectory analysis shows that (1) the area per lipid is mostly correlated to the acyl chain number, and the area per lipid increases as a function of the acyl chain number; (2) the hydrophobic thickness is mainly determined by the average acyl chain length with slight dependence on the acyl chain number, and the hydrophobic thickness generally increases with the average acyl chain length; (3) a good correlation is observed among the area per lipid, hydrophobic thickness, and acyl chain order; and (4) although the influence of neutralizing ion types on the area per lipid and hydrophobic thickness is minimal, Ca²⁺ stays longer on the membrane surface than K⁺ or Na⁺, consequently leading to lower lateral diffusion and a higher compressibility modulus, which agrees well with available experiments.

MetQ of Neisseria gonorrhoeae Is a Surface-Expressed Antigen That Elicits Bactericidal and Functional Blocking Antibodies

Neisseria gonorrhoeae, the causative agent of the sexually transmitted infection (STI) gonorrhea, is a growing public health threat for which a vaccine is urgently needed. We characterized the functional role of the gonococcal MetQ protein, which is the methionine binding component of an ABC transporter system, and assessed its potential as a candidate antigen for inclusion in a gonococcal vaccine. MetQ has been found to be highly conserved in all strains investigated to date, it is localized on the bacterial surface, and it binds l-methionine with a high affinity. MetQ is also involved in gonococcal adherence to cervical epithelial cells. Mutants lacking MetQ have impaired survival in human monocytes, macrophages, and serum. Furthermore, antibodies raised against MetQ are bactericidal and are able to block gonococcal adherence to epithelial cells. These data suggest that MetQ elicits both bactericidal and functional blocking antibodies and is a valid candidate antigen for additional investigation and possible inclusion in a vaccine for prevention of gonorrhea.

Is gonococcal disease preventable? The importance of understanding immunity and pathogenesis in vaccine development

Gonorrhea is a major, global public health problem for which there is no vaccine. The continuing emergence of antibiotic-resistant strains raises concerns that untreatable Neisseria gonorrhoeae may become widespread in the near future. Consequently, there is an urgent need for increased efforts towards the development of new anti-gonococcal therapeutics and vaccines, as well as suitable models for potential pre-clinical vaccine trials. Several current issues regarding gonorrhea are discussed herein, including the global burden of disease, the emergence of antibiotic-resistance, the status of vaccine development and, in particular, a focus on the model systems available to evaluate drug and vaccine candidates. Finally, alternative approaches to evaluate vaccine candidates are presented. Such approaches may provide valuable insights into the protective mechanisms, and correlates of protection, required to prevent gonococcal transmission, local infection and disease sequelae.

Seminal Plasma Promotes Neisseria gonorrhoeae Aggregation and Biofilm Formation

Neisseria gonorrhoeae causes the human-specific disease gonorrhea and is transmitted from person to person primarily via sexual contact. During transmission, N. gonorrhoeae is often exposed to seminal fluid and must adapt to this change in environment. Previous work demonstrated that seminal fluid facilitates N. gonorrhoeae motility and alters epithelial cell interactions. In this study, exposure to seminal fluid was found to decrease surface adherence of gonococci in a manner that was independent of Opa adhesin proteins or type IV pilus retraction. Semen was also shown to cause dispersal of bacteria that had previously established surface adherence. Although surface adherence decreased, interbacterial interactions were increased by seminal plasma both in long-term static culture and on a cell-to-cell basis over shorter time periods. The result of increased bacterium-bacterium interactions resulted in the formation of microcolonies, an important step in the N. gonorrhoeae infectious process. Seminal fluid also facilitated increased bacterial aggregation in the form of shear-resistant three-dimensional biofilms. These results emphasize the importance of the gonococcal response to the influx of seminal fluid within the genital niche. Further characterization of the N. gonorrhoeae response to semen will advance our understanding of the mechanisms behind the establishment of infection in naive hosts and the process of transmission.

IMPORTANCE

N. gonorrhoeae is the causative agent of the globally prevalent sexually transmitted infection gonorrhea. An understudied aspect of this human-adapted pathogen is the change in bacterial physiology that occurs during sexual transmission. N. gonorrhoeae encounters semen when transmitted from host to host, and it is known that, when N. gonorrhoeae is exposed to seminal fluid, alterations in bacterial motility and type IV pilus arrangement occur. This work extends our previous observations on this modulation of gonococcal physiology by seminal fluid and demonstrates that seminal plasma decreases surface adherence, promotes interbacterial interactions, and enhances biofilm formation.

Desialylation of Neisseria gonorrhoeae Lipooligosaccharide by Cervicovaginal Microbiome Sialidases: The Potential for Enhancing Infectivity in Men

Previous studies have demonstrated that Neisseria gonorrhoeae sialylates the terminal N-acetyllactosamine present on its lipooligosaccharide (LOS) by acquiring CMP-N-acetyl-5-neuraminic acid upon entering human cells during infection. This renders the organism resistant to killing by complement in normal human serum. N-acetyllactosamine residues on LOS must be free of N-acetyl-5-neuraminc acid (Neu5Ac; also known as "sialic acid") in order for organisms to bind to and enter urethral epithelial cells during infection in men. This raises the question of how the gonococcus infects men if N-acetyllactosamine residues are substituted by Neu5Ac during infection in women. Here, we demonstrate that women with gonococcal infections have levels of sialidases present in cervicovaginal secretions that can result in desialylation of (sialylated) gonococcal LOS. The principle sialidases responsible for this desialylation appear to be bacterial in origin. These studies suggest that members of the cervicovaginal microbiome can modify N. gonorrhoeae, which will enhance successful transmission to men.

Lactobacillus crispatus inhibits growth of Gardnerella vaginalis and Neisseria gonorrhoeae on a porcine vaginal mucosa model

Background

The vaginal microbiota can impact the susceptibility of women to bacterial vaginosis (BV) and sexually transmitted infections (STIs). BV is characterized by depletion of Lactobacillus spp., an overgrowth of anaerobes (often dominated by Gardnerella vaginalis) and a pH > 4.5. BV is associated with an increased risk of acquiring STIs such as chlamydia and gonorrhea. While these associations have been identified, the molecular mechanism(s) driving the risk of infections are unknown. An ex vivo porcine vaginal mucosal model (PVM) was developed to explore the mechanistic role of Lactobacillus spp. in affecting colonization by G. vaginalis and Neisseria gonorrhoeae.

Results

The data presented here demonstrate that all organisms tested can colonize and grow on PVM to clinically relevant densities. Additionally, G. vaginalis and N. gonorrhoeae form biofilms on PVM. It was observed that lactic acid, acetic acid, and hydrochloric acid inhibit the growth of G. vaginalis on PVM in a pH-dependent manner. N. gonorrhoeae grows best in the presence of lactic acid at pH 5.5, but did not grow well at this pH in the presence of acetic acid. Finally, a clinical Lactobacillus crispatus isolate (24-9-7) produces lactic acid and inhibits growth of both G. vaginalis and N. gonorrhoeae on PVM.

Conclusions

These data reveal differences in the effects of pH, various acids and L. crispatus on the growth of G. vaginalis and N. gonorrhoeae on a live vaginal mucosal surface. The PVM is a useful model for studying the interactions of commensal vaginal microbes with pathogens and the mechanisms of biofilm formation on the vaginal mucosa.

Neisseria gonorrhoeae Modulates Cell Death in Human Endocervical Epithelial Cells through Export of Exosome-Associated cIAP2

Several bacterial pathogens persist and survive in the host by modulating host cell death pathways. We previously demonstrated that Neisseria gonorrhoeae, a Gram-negative pathogen responsible for the sexually transmitted infection gonorrhea, protects against exogenous induction of apoptosis in human cervical epithelial cells. However, induction of cell death by N. gonorrhoeae has also been reported in other cell types. The mechanisms by which N. gonorrhoeae modulates cell death are not clear, although a role for the inhibitor of apoptosis-2 (cIAP2) has been proposed. In this study, we confirmed that N. gonorrhoeae induces production of cIAP2 in human cervical epithelial cells. High levels of intracellular cIAP2 were detected early after N. gonorrhoeae stimulation, which was followed by a marked decrease at 24 h. At this time point, we observed increased levels of extracellular cIAP2 associated with exosomes and an overall increase in production of exosomes. Inhibition of cIAP2 in N. gonorrhoeae-stimulated epithelial cells resulted in increased cell death and interleukin-1β (IL-1β) production. Collectively these results indicate that N. gonorrhoeae stimulation of human endocervical epithelial cells induces the release of cIAP2, an essential regulator of cell death and immune signaling.

A role for lactate dehydrogenases in the survival of Neisseria gonorrhoeae in human polymorphonuclear leukocytes and cervical epithelial cells

Lactate is an abundant metabolite, produced by host tissues and commensal organisms, and it represents an important potential carbon source for bacterial pathogens. In the case of Neisseria spp., the importance of the lactate permease in colonization of the host has been demonstrated, but there have been few studies of lactate metabolism in pathogenic Neisseria in the postgenomic era. We describe herein the characterization of genome-annotated, respiratory, and substrate-level lactate dehydrogenases (LDHs) from the obligate human pathogen Neisseria gonorrhoeae. Biochemical assays using N. gonorrhoeae 1291 wild type and isogenic mutant strains showed that cytoplasmic LdhA (NAD(+)-dependent D-lactate dehydrogenase) and the membrane-bound respiratory enzymes, LdhD (D-lactate dehydrogenase) and LldD (L-lactate dehydrogenase) are correctly annotated. Mutants lacking LdhA and LdhD showed greatly reduced survival in neutrophils compared with wild type cells, highlighting the importance of D-lactate metabolism in gonococcal survival. Furthermore, an assay of host colonization using the well-established human primary cervical epithelial cell model revealed that the two respiratory enzymes make a significant contribution to colonization of and survival within the microaerobic environment of the host. Taken together, these data suggest that host-derived lactate is critical for the growth and survival of N. gonorrhoeae in human cells.

Inflammatory stimuli reprogram macrophage phagocytosis to macropinocytosis for the rapid elimination of pathogens

Following an infectious challenge, macrophages have to be activated in order to allow efficient clearance of infectious pathogens, but how macrophage activation is coupled to increased clearance remains largely unknown. We here describe that inflammatory stimuli induced the reprogramming of the macrophage endocytic machinery from receptor-mediated phagocytosis to macropinocytosis, allowing the rapid transfer of internalized cargo to lysosomes in a receptor-independent manner. Reprogramming occurred through protein kinase C-mediated phosphorylation of the macrophage protein coronin 1, thereby activating phosphoinositol (PI)-3-kinase activity necessary for macropinocytic uptake. Expression of a phosphomimetic form of coronin 1 was sufficient to induce PI3-kinase activation and macropinocytosis even in the absence of inflammatory stimuli. Together these results suggest a hitherto unknown mechanism to regulate the internalization and degradation of infectious material during inflammation.

The main cells that are involved in cleaning up microbial pathogens are macrophages. Upon an infection, macrophages are being recruited to the site of infection by a number of different stimuli. In addition, during an infection, macrophages are also activated by cytokines such as interferon-γ and tumor necrosis factor-α that is released from other immune cells. Such macrophage activation is important to achieve a rapid and efficient clearance of microbial pathogens. In this study, we found that macrophage activation induces uptake through macropinocytosis rather than receptor-mediate phagocytosis. As a consequence, microbial material as well as particles can be internalized far more efficiently; In addition, the internalized cargo is rapidly destroyed within lysosomes. We also provide the mechanisms for the switch from phagocytosis to macropinocytosis, which turned out to be the cytokine-induced phosphorylation of the host protein coronin 1. Phosphorylated coronin 1 activated the lipid kinase phosphoinositide 3-kinase, which is known to be responsible for the entry of cargo through macropinocytosis. Together these results provide evidence for a hitherto unrecognized mechanisms to regulate the internalization and degradation of infectious material during an infection.

Dual pili post-translational modifications synergize to mediate meningococcal adherence to platelet activating factor receptor on human airway cells

Pili of pathogenic Neisseria are major virulence factors associated with adhesion, twitching motility, auto-aggregation, and DNA transformation. Pili of N. meningitidis are subject to several different post-translational modifications. Among these pilin modifications, the presence of phosphorylcholine (ChoP) and a glycan on the pilin protein are phase-variable (subject to high frequency, reversible on/off switching of expression). In this study we report the location of two ChoP modifications on the C-terminus of N. meningitidis pilin. We show that the surface accessibility of ChoP on pili is affected by phase variable changes to the structure of the pilin-linked glycan. We identify for the first time that the platelet activating factor receptor (PAFr) is a key, early event receptor for meningococcal adherence to human bronchial epithelial cells and tissue, and that synergy between the pilin-linked glycan and ChoP post-translational modifications is required for pili to optimally engage PAFr to mediate adherence to human airway cells.

Neisseria meningitidis is an important human pathogen that can cause rapidly progressing, life threatening meningitis and sepsis in humans. There is no fully protective vaccine against this pathogen in current use and the key processes that dictate the transition from harmless carriage of the bacterium in the airway (the case for the vast majority of colonised hosts) to invasive disease are largely undefined. A key missing link in this organism's interaction with the human host is the identity of the receptor that is the first point of contact for the organism within the airway. In this study, we report that the receptor for this important human pathogen on airway epithelial cells is the platelet activating factor receptor (PAFr), an immunomodulatory molecule shown by others to play a role in promoting bacterial sepsis. We also show that two post-translational modifications, glycosylation and phosphorylcholine, are subject to phase-variation (high frequency, reversible switching of gene expression). They are closely associated on adjacent pilin subunits, and synergy between both are required for the efficient engagement with the PAFr. These data define a new role for these post-translational modifications in meningococcal adherence and also provide an insight into the selective pressures that underlie their phase variable expression.

Comparison study of single and concurrent administrations of carbapenem, new quinolone, and macrolide against in vitro nontypeable Haemophilus influenzae mature biofilms

Nontypeable Haemophilus influenzae (NTHi) is an opportunistic pathogen and a common cause of otitis media in children, chronic bronchitis, and pneumonia in patients with chronic obstructive pulmonary disease. Many studies have reported that NTHi is capable of producing biofilms, which may be one of the important factors involved in chronic diseases and accelerating antimicrobial resistance. Unfortunately, there is still no consensus about the elimination of biofilms. In this study, concurrent administrations of levofloxacin (LVFX)-imipenem (IPM) and clarithromycin (CAM)-IPM, as well as the single administration of IPM, LVFX, and CAM, were performed to treat the mature biofilms produced by NTHi, respectively. Biofilm inhibition was quantified using microtiter biofilm assay (MBA), and relative biomass was calculated as the ratio compared to that of untreated control biofilms. The relative biomasses of biofilms treated with IPM, LVFX-IPM, and CAM-IPM against a β-lactamase-negative ampicillin-resistant strain was 1.10, 0.08, and 0.13 at 1× minimum inhibitory concentration (MIC), 0.90, 0.05, and 0.07 at 10× MIC, and 0.80, 0.06, and 0.07 at 100× MIC, respectively. Biofilms were also visually observed by scanning electron microscopy, and a focused ion-beam system showed that high concentrations of combined administration strongly inhibited the biofilms, which was consistent with the results of MBA. Our data demonstrated the antibiofilm effect of concurrent administration against mature NTHi biofilms, which indicated a rationale for the potential use of concurrent administrations in diseases involving chronic NTHi biofilms.

Characterization of an ntrX mutant of Neisseria gonorrhoeae reveals a response regulator that controls expression of respiratory enzymes in oxidase-positive proteobacteria

NtrYX is a sensor-histidine kinase/response regulator two-component system that has had limited characterization in a small number of Alphaproteobacteria. Phylogenetic analysis of the response regulator NtrX showed that this two-component system is extensively distributed across the bacterial domain, and it is present in a variety of Betaproteobacteria, including the human pathogen Neisseria gonorrhoeae. Microarray analysis revealed that the expression of several components of the respiratory chain was reduced in an N. gonorrhoeae ntrX mutant compared to that in the isogenic wild-type (WT) strain 1291. These included the cytochrome c oxidase subunit (ccoP), nitrite reductase (aniA), and nitric oxide reductase (norB). Enzyme activity assays showed decreased cytochrome oxidase and nitrite reductase activities in the ntrX mutant, consistent with microarray data. N. gonorrhoeae ntrX mutants had reduced capacity to survive inside primary cervical cells compared to the wild type, and although they retained the ability to form a biofilm, they exhibited reduced survival within the biofilm compared to wild-type cells, as indicated by LIVE/DEAD staining. Analyses of an ntrX mutant in a representative alphaproteobacterium, Rhodobacter capsulatus, showed that cytochrome oxidase activity was also reduced compared to that in the wild-type strain SB1003. Taken together, these data provide evidence that the NtrYX two-component system may be a key regulator in the expression of respiratory enzymes and, in particular, cytochrome c oxidase, across a wide range of proteobacteria, including a variety of bacterial pathogens.

Glutathione reductase facilitates host defense by sustaining phagocytic oxidative burst and promoting the development of neutrophil extracellular traps

Glutathione reductase (Gsr) catalyzes the reduction of glutathione disulfide to glutathione, which plays an important role in the bactericidal function of phagocytes. Because Gsr has been implicated in the oxidative burst in human neutrophils and is abundantly expressed in the lymphoid system, we hypothesized that Gsr-deficient mice would exhibit marked defects during the immune response against bacterial challenge. We report in this study that Gsr-null mice exhibited enhanced susceptibility to Escherichia coli challenge, indicated by dramatically increased bacterial burden, cytokine storm, striking histological abnormalities, and substantially elevated mortality. Additionally, Gsr-null mice exhibited elevated sensitivity to Staphylococcus aureus. Examination of the bactericidal functions of the neutrophils from Gsr-deficient mice in vitro revealed impaired phagocytosis and defective bacterial killing activities. Although Gsr catalyzes the regeneration of glutathione, a major cellular antioxidant, Gsr-deficient neutrophils paradoxically produced far less reactive oxygen species upon activation both ex vivo and in vivo. Unlike wild-type neutrophils that exhibited a sustained oxidative burst upon stimulation with phorbol ester and fMLP, Gsr-deficient neutrophils displayed a very transient oxidative burst that abruptly ceased shortly after stimulation. Likewise, Gsr-deficient neutrophils also exhibited an attenuated oxidative burst upon encountering E. coli. Biochemical analysis revealed that the hexose monophosphate shunt was compromised in Gsr-deficient neutrophils. Moreover, Gsr-deficient neutrophils displayed a marked impairment in the formation of neutrophil extracellular traps, a bactericidal mechanism that operates after neutrophil death. Thus, Gsr-mediated redox regulation is crucial for bacterial clearance during host defense against massive bacterial challenge.

Novel bacterial MerR-like regulators their role in the response to carbonyl and nitrosative stress

Recognition of the diversity of transcriptional regulators of the MerR family has increased considerably over the last decade and it has been established that not all MerR-like regulators are involved in metal ion recognition. A new type of MerR-like regulator was identified in Neisseria gonorrhoeae that is distinct from metal-binding MerR proteins. This novel transcription factor, the Neisseria merR-like regulator (NmlR) is related to a large and diverse group of MerR-like regulators. A common feature of the majority of the genes encoding the nmlR-related genes is that they predicted to control the expression of adhC, which encodes a glutathione-dependent alcohol dehydrogenase. The function of the NmlR regulon appears to be to defend the bacterial cell against carbonyl stress and in some cases nitrosative stress. A potential role for NmlR in bacterial pathogenesis has been identified in Neisseria gonorrhoeae and Streptococcus pneumoniae. Although it is not known how NmlR is activated it is suggested that conserved cysteine residues may be involved in thiol-based signaling.

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.

Neisseria gonorrhoeae pilin glycan contributes to CR3 activation during challenge of primary cervical epithelial cells

Expression of type IV pili by Neisseria gonorrhoeae plays a critical role in mediating adherence to human epithelial cells. Gonococcal pilin is modified with an O-linked glycan, which may be present as a di- or monosaccharide because of phase variation of select pilin glycosylation genes. It is accepted that bacterial proteins may be glycosylated; less clear is how the protein glycan may mediate virulence. Using primary, human, cervical epithelial (i.e. pex) cells, we now provide evidence to indicate that the pilin glycan mediates productive cervical infection. In this regard, pilin glycan-deficient mutant gonococci exhibited an early hyper-adhesive phenotype but were attenuated in their ability to invade pex cells. Our data further indicate that the pilin glycan was required for gonococci to bind to the I-domain region of complement receptor 3, which is naturally expressed by pex cells. Comparative, quantitative, infection assays revealed that mutant gonococci lacking the pilin glycan did not bind to the I-domain when it is in a closed, low-affinity conformation and cannot induce an active conformation to complement receptor 3 during pex cell challenge. To our knowledge, these are the first data to directly demonstrate how a protein-associated bacterial glycan may contribute to pathogenesis.

Factor H facilitates adherence of Neisseria gonorrhoeae to complement receptor 3 on eukaryotic cells

Neisseria gonorrhoeae can engage human complement receptor 3 (CR3) directly or through surface-bound iC3b. Factor H (fH) that binds to bacteria facilitates conversion of C3b to iC3b. fH also binds directly to CR3 on professional phagocytes. Certain nonprofessional phagocytes, such as primary cervical epithelial cells, also express CR3. We hypothesized that fH could bridge bacteria to CR3 and facilitate gonococcal association with host cells. Specificity of the fH-CR3 interaction was confirmed using human CR3-transfected Chinese hamster ovary (CHO-CR3) cells. Using recombinant proteins that comprised contiguous fH domains (fH contains 20 short consensus repeat [SCR] domains) fused to murine Fc, we observed strong binding through SCRs 18-20, whereas weaker binding occurred through SCRs 6-10. Both regions also bound to unsialylated porin (Por) B.1A-expressing N. gonorrhoeae. Accordingly, fH-related protein 1 (three of its five SCRs are highly homologous to fH SCRs 18-20) bound to CHO-CR3 and to unsialylated PorB.1A gonococci. An alternatively spliced variant of fH called fH-like protein-1 (contains fH SCRs 1-7) bound to gonococci but minimally to CHO-CR3. An fH SCRs 6-20 construct enhanced binding of unsialylated PorB.1A gonococci to CHO-CR3. However, a construct that contained only the apparently relevant SCRs (6, 7, and 18-20) bound to CHO-CR3 and to gonococci separately, but did not enhance bacteria-CR3 interactions, suggesting that the intervening SCRs (8-17) may impart a configurational and spatial requirement for fH to bridge gonococci to CR3. These results indicate adherence between fH-coated gonococci and CR3 and may provide a means for gonococci to gain sanctuary into nonprofessional phagocytes.

Type IV secretion machinery promotes ton-independent intracellular survival of Neisseria gonorrhoeae within cervical epithelial cells

Survival of Neisseria gonorrhoeae within host epithelial cells is expected to be important in the pathogenesis of gonococcal disease. We previously demonstrated that strain FA1090 derives iron from a host cell in a process that requires the Ton complex and a putative TonB-dependent transporter, TdfF. FA1090, however, lacks the gonococcal genetic island (GGI) that is present in the majority of strains. The GGI in strain MS11 has been partially characterized, and it encodes a type IV secretion system (T4SS) involved in DNA release. In this study we investigated the role of iron acquisition and GGI-encoded gene products in gonococcal survival within cervical epithelial cells. We demonstrated that intracellular survival of MS11 was dependent on acquisition of iron from the host cell, but unlike the findings for FA1090, expression of the Ton complex was not required. Survival was not dependent on a putative TonB-like protein encoded in the GGI but instead was directly linked to T4SS structural components in a manner independent of the ability to release or internalize DNA. These data suggest that expression of selected GGI-encoded open reading frames confers an advantage during cervical cell infection. This study provides the first link between expression of the T4SS apparatus and intracellular survival of gonococci.

Neisseria gonorrhoeae survival during primary human cervical epithelial cell infection requires nitric oxide and is augmented by progesterone

Neisseria gonorrhoeae is an obligate human pathogen that causes gonorrhea. We have shown previously that complement receptor 3 and Akt kinase play important roles in mediating cervical infection. At present, there are limited data to indicate how hormonally induced changes to the mucosal epithelia of the female genital tract mediate the course of gonococcal disease. Hence, I have expanded upon previous work to investigate the interaction of gonococci with primary human cervical epithelial (pex) cells under the variable estrogen and progesterone concentrations likely to be encountered in vivo throughout the female menstrual cycle. My data indicated that the ability of gonococci to survive and to replicate within pex cells was increased under progesterone-predominant conditions. Using bacterial survival, immunological, and kinase assays, I show that progesterone functioned in an additive manner with gonococcal phospholipase D to augment Akt kinase activity. This, in turn, resulted in a parallel increase in nitric oxide synthase expression. Nitric oxide production by pex cells was dependent upon Akt activity and was increased under progesterone-predominant conditions. Whereas both inducible and endothelial nitric oxide synthase contributed to nitric oxide production, only inducible nitric oxide synthase activity promoted gonococcal survival within pex cells. Collectively, these data provide the first clues as to how steroid hormones potentially modulate the course of gonococcal disease in women. In addition, these data demonstrate that host-derived nitric oxide likely is not protective against gonococci, in vivo; rather, nitric oxide may be required to sustain cervical bacterial disease.

Manganese regulation of virulence factors and oxidative stress resistance in Neisseria gonorrhoeae

Neisseria gonorrhoeae has evolved a complex and novel network of oxidative stress responses, including defence mechanisms that are dependent on manganese (Mn). We performed systematic analyses at the transcriptomic and proteomic (1D SDS-PAGE and Isotope-Coded Affinity Tag [ICAT]) levels to investigate the global expression changes that take place in a high Mn environment, which results in a Mn-dependent oxidative stress resistance phenotype. These studies revealed that there were proteins regulated at the post-transcriptional level under conditions of increased Mn concentration, including proteins involved in virulence (e.g., pilin, a key adhesin), oxidative stress defence (e.g., superoxide dismutase), cellular metabolism, protein synthesis, RNA processing and cell division. Mn regulation of inorganic pyrophosphatase (Ppa) indicated the potential involvement of phosphate metabolism in the Mn-dependent oxidative stress defence. A detailed analysis of the role of Ppa and polyphosphate kinase (Ppk) in the gonococcal oxidative stress response revealed that ppk and ppa mutant strains showed increased resistance to oxidative stress. Investigation of these mutants grown with high Mn suggests that phosphate and pyrophosphate are involved in Mn-dependent oxidative stress resistance.

Influence of type IV pilus retraction on the architecture of the Neisseria gonorrhoeae-infected cell cortex

Early in infection, Neisseria gonorrhoeae can be observed to attach to the epithelial cell surface as microcolonies and induce dramatic changes to the host cell cortex. We tested the hypothesis that type IV pili (Tfp) retraction plays a role in the ultrastructure of both the host cell cortex and the bacterial microcolony. Using serial ultrathin sectioning, transmission electron microscopy and 3D reconstruction of serial 2D images, we have obtained what we believe to be the first 3D reconstructions of the N. gonorrhoeae-host cell interface, and determined the architecture of infected cell microvilli as well as the attached microcolony. Tfp connect both wild-type (wt) and Tfp retraction-deficient bacteria with each other, and with the host cell membrane. Tfp fibres and microvilli form a lattice in the wt microcolony and at its periphery. Wt microcolonies induce microvilli formation and increases of surface area, leading to an approximately ninefold increase in the surface area of the host cell membrane at the site of attachment. In contrast, Tfp retraction-deficient microcolonies do not affect these parameters. Wt microcolonies had a symmetrical, dome-shaped structure with a circular 'footprint', while Tfp retraction-deficient microcolonies were notably less symmetrical. These findings support a major role for Tfp retraction in microvilli and microcolony architecture. They are consistent with the biophysical attributes of Tfp and the effects of Tfp retraction on epithelial cell signalling.

The role of complement in gonococcal infection of cervical epithelia

Neisseria gonorrhoeae is an exclusive human pathogen that causes the sexually transmitted disease, gonorrhea. The gonococcus has developed an exquisite repertoire of mechanisms by which it is able to evade host innate and adaptive immune responses. Our previous data indicate that the predominately asymptomatic nature ofgonococcal cervicitis may, in part, be attributed to the ability of these bacteria to subvert the normal function of complement to promote cervical disease. Herein we describe the interaction of N. gonorrhoeae with the complement alternative pathway with a particular focus on the importance of this interaction in promoting gonococcal cervicitis.

Phasevarions mediate random switching of gene expression in pathogenic Neisseria

Many host-adapted bacterial pathogens contain DNA methyltransferases (mod genes) that are subject to phase-variable expression (high-frequency reversible ON/OFF switching of gene expression). In Haemophilus influenzae, the random switching of the modA gene controls expression of a phase-variable regulon of genes (a “phasevarion”), via differential methylation of the genome in the modA ON and OFF states. Phase-variable mod genes are also present in Neisseria meningitidis and Neisseria gonorrhoeae, suggesting that phasevarions may occur in these important human pathogens. Phylogenetic studies on phase-variable mod genes associated with type III restriction modification (R-M) systems revealed that these organisms have two distinct mod genes—modA and modB. There are also distinct alleles of modA (abundant: modA11, 12, 13; minor: modA4, 15, 18) and modB (modB1, 2). These alleles differ only in their DNA recognition domain. ModA11 was only found in N. meningitidis and modA13 only in N. gonorrhoeae. The recognition site for the modA13 methyltransferase in N. gonorrhoeae strain FA1090 was identified as 5′-AGAAA-3′. Mutant strains lacking the modA11, 12 or 13 genes were made in N. meningitidis and N. gonorrhoeae and their phenotype analyzed in comparison to a corresponding mod ON wild-type strain. Microarray analysis revealed that in all three modA alleles multiple genes were either upregulated or downregulated, some of which were virulence-associated. For example, in N. meningitidis MC58 (modA11), differentially expressed genes included those encoding the candidate vaccine antigens lactoferrin binding proteins A and B. Functional studies using N. gonorrhoeae FA1090 and the clinical isolate O1G1370 confirmed that modA13 ON and OFF strains have distinct phenotypes in antimicrobial resistance, in a primary human cervical epithelial cell model of infection, and in biofilm formation. This study, in conjunction with our previous work in H. influenzae, indicates that phasevarions may be a common strategy used by host-adapted bacterial pathogens to randomly switch between “differentiated” cell types.

The pathogenic Neisseria are bacterial pathogens that cause meningitis and gonorrhoea. They have adapted to life exclusively in humans and have developed unique strategies to colonize the host and to evade the immune response. Central among these strategies are genetic switches that randomly turn genes on and off. In most cases, the genes controlled by these switches, contingency genes, are required for making bacterial surface structures. Recently we described a new class of contingency gene that methylates DNA. Rather than affecting the synthesis of a single surface structure, on/off switching of this DNA-methyltransferase gene leads to random switching of multiple genes. In this study, we have shown that this mechanism exists in all pathogenic Neisseria, and alters expression of multiple genes in all cases we examined. The two distinct populations of bacteria generated by this process had different behavior in model systems of colonization and infection. Understanding this process is key to understanding these human pathogens, and to developing strategies for treatment and prevention of the diseases they cause.

Thioredoxin reductase is essential for protection of Neisseria gonorrhoeae against killing by nitric oxide and for bacterial growth during interaction with cervical epithelial cells

In Neisseria gonorrhoeae, the MerR family transcription factor NmlR activates 3 operons in response to disulfide stress. In the present study, we show that trxB, a monocistronic operon under the control of NmlR, encodes a functional thioredoxin reductase. It is shown that neisserial TrxB has biochemical properties similar to those of its homologue from Escherichia coli. Analysis of a trxB mutant of N. gonorrhoeae showed that it was more sensitive to disulfide stress and to stress induced by organic hydroperoxides, superoxide, and nitric oxide than wild-type gonococcus. TrxB was found to be essential for the microaerobic induction of aniA and norB, the genes encoding nitrite reductase and nitric oxide reductase, respectively. The importance of TrxB during natural infection was demonstrated by the fact that the survival of gonococci within human cervical epithelial cells, as well as biofilm formation on these cells, was greatly reduced for a trxB mutant compared with a wild-type strain.

Nosocomial bacteremia caused by biofilm-forming Bacillus cereus and Bacillus thuringiensis

OBJECTIVE

Bacterial biofilms cause serious problems, such as antibiotic resistance and medical device-related infections. Recent reports indicate that Bacillus species potentially form biofilms and cause nosocomial bacteremia via catheter infection. Our objective was to investigate the relationship between nosocomial bacteremia caused by Bacillus species and biofilm formations.

METHODS

Between 2001 and 2006, Bacillus cereus and Bacillus thuringiensis were isolated from blood samples of 21 patients with nosocomial bacteremia in two hospitals. The patients had underlying diseases such as cerebrovascular damage, malignant disease, or chronic obstructive lung disease and had high fever at the onset of bacteremia. After investigation, B. cereus and B. thuringiensis were isolated from patient's catheter tip, gauze, and hospital environment. Pulsed-field gel electrophoresis (PFGE) on 32 B. cereus and 7 B. thuringiensis isolates, microtiter biofilm assay and scanning electron microscopy (SEM) on 22 B. cereus isolates from patient's blood were performed.

RESULTS

Molecular analysis by PFGE showed that 32 B. cereus strains had 21 patterns and 7 B. thuringiensis strains had 3 patterns. The PFGE patterns of B. thuringiensis and B. cereus in blood samples from 2 patients blood were similar to those from the same patient's catheter tip. The PFGE pattern of B. cereus from a hospital environment was similar to that from 2 patients' blood samples, and the PFGE pattern of B. thuringiensis from 2 hospital environments was similar to that from 2 patients' blood. The biofilm formations by 22 B. cereus isolates from patients' blood were confirmed by microtiter biofilm assay and SEM even at 24 hours.

CONCLUSION

Our data indicate that various types of Bacillus species exist in hospital environments and the biofilm-forming strains potentially cause nosocomial bacteremia by catheter infection.

Morphology of human Fallopian tubes after infection with Mycoplasma genitalium and Mycoplasma hominis--in vitro organ culture study

BACKGROUND

Female infertility can be caused by scarring and occlusion of the Fallopian tubes. Sexually transmitted bacteria can damage the delicate epithelial layer of human Fallopian tubes (HFT). Genital mycoplasmas are associated with human reproductive failure. Yet, there is not enough evidence that mycoplasmas can cause tubal factor infertility. We analysed the effects of infections with Mycoplasma hominis and Mycoplasma genitalium on the HFT epithelium and compared them with the effects of infections with genital pathogens: Chlamydia trachomatis and Neisseria gonorrhoeae.

METHODS

We used an in vitro model in which pieces of normal HFT were infected with different bacteria, and the outcome of the infections was analysed by scanning electron microscopy (SEM) and confocal microscopy.

RESULTS

The presence of M. hominis did not cause any morphological changes of the epithelium of HFT. Noticeable changes in the morphology of the ciliated cells were observed in M. genitalium-infected tissue. Five days post-infection, the cilia were abnormally swollen and some of the ciliated cells fell off the epithelium. These effects could be inhibited by pre-incubation of M. genitalium with antibody directed against the C-terminal part of the adhesion protein MgPa before infection of HFT organ culture.

CONCLUSION

We have shown that the presence of M. genitalium, but not M. hominis, in the HFT organ culture affected the epithelium and resulted in cilia damage. The effect of infection with M. genitalium on the HFT was, however, very moderate when compared with the extensive damage of the epithelium caused by N. gonorrhoeae or C. trachomatis.

Characterization of the OxyR regulon of Neisseria gonorrhoeae

OxyR regulates the expression of the majority of H(2)O(2) responses in Gram-negative organisms. In a previous study we reported the OxyR-dependent derepression of catalase expression in the human pathogen Neisseria gonorrhoeae. In the present study we used microarray expression profiling of N. gonorrhoeae wild-type strain 1291 and an oxyR mutant strain to define the OxyR regulon. In addition to katA (encoding catalase), only one other locus displayed a greater than two-fold difference in expression in the wild type : oxyR comparison. This locus encodes an operon of two genes, a putative peroxiredoxin/glutaredoxin (Prx) and a putative glutathione oxidoreductase (Gor). Mutant strains were constructed in which each of these genes was inactivated. A previous biochemical study in Neisseria meningitidis had confirmed function of the glutaredoxin/peroxiredoxin. Assay of the wild-type 1291 cell free extract confirmed Gor activity, which was lost in the gor mutant strain. Phenotypic analysis of the prx mutant strain in H(2)O(2) killing assays revealed increased resistance, presumably due to upregulation of alternative defence mechanisms. The oxyR, prx and gor mutant strains were deficient in biofilm formation, and the oxyR and prx strains had decreased survival in cervical epithelial cells, indicating a key role for the OxyR regulon in these processes.

Neisseria gonorrhoeae PLD directly interacts with Akt kinase upon infection of primary, human, cervical epithelial cells

Neisseria gonorrhoeae secrets a phospholipase D (NgPLD), which augments complement receptor 3 (CR3)-mediated invasion of cervical epithelial cells. To elucidate the signalling pathways triggered with gonococcus CR3-engagement and the putative function of NgPLD in these events, we analysed the contribution of the phosphoinositide-Akt pathway to cervical infection. Our data indicated that Akt plays a critical role in cervical infection. Inhibition of myosin light chain kinase, PtdIns(4,5)P2, and Akt functions resulted in decreased gonococcus invasion of primary, human, cervical epithelial cells as well as Akt kinase activity. Akt activity was similarly impaired when cervical cells were challenged with NgPLD-mutant gonococci. Conversely, the PI3-kinase inhibitor, LY294002, enhanced gonococcal invasion of, and Akt activity within, primary cervical cells. We demonstrated that NgPLD directly binds to the Akt PH domain and can compete with a natural Akt ligand, PtdIns(3,4,5)P3, for Akt binding. Collectively, our data suggested that NgPLD augments gonococcus invasion of cervical epithelia by interacting with Akt kinase in a PI3-kinase-independent manner, which results in subversion of normal cervical cell signalling.

PerR controls Mn-dependent resistance to oxidative stress in Neisseria gonorrhoeae

In previous studies it has been established that resistance to superoxide by Neisseria gonorrhoeae is dependent on the accumulation of Mn(II) ions involving the ABC transporter, MntABC. A mutant strain lacking the periplasmic binding protein component (MntC) of this transport system is hypersensitive to killing by superoxide anion. In this study the mntC mutant was found to be more sensitive to H2O2 killing than the wild-type. Analysis of regulation of MntC expression revealed that it was de-repressed under low Mn(II) conditions. The N. gonorrhoeae mntABC locus lacks the mntR repressor typically found associated with this locus in other organisms. A search for a candidate regulator of mntABC expression revealed a homologue of PerR, a Mn-dependent peroxide-responsive regulator found in Gram-positive organisms. A perR mutant expressed more MntC protein than wild-type, and expression was independent of Mn(II), consistent with a role for PerR as a repressor of mntABC expression. The PerR regulon of N. gonorrhoeae was defined by microarray analysis and includes ribosomal proteins, TonB-dependent receptors and an alcohol dehydrogenase. Both the mntC and perR mutants had reduced intracellular survival in a human cervical epithelial cell model.

Defenses against oxidative stress in Neisseria gonorrhoeae: a system tailored for a challenging environment

Neisseria gonorrhoeae is a host-adapted pathogen that colonizes primarily the human genitourinary tract. This bacterium encounters reactive oxygen and reactive nitrogen species as a consequence of localized inflammatory responses in the urethra of males and endocervix of females and also of the activity of commensal lactobacilli in the vaginal flora. This review describes recent advances in the understanding of defense systems against oxidative stress in N. gonorrhoeae and shows that while some of its defenses have similarities to the paradigm established with Escherichia coli, there are also some key differences. These differences include the presence of a defense system against superoxide based on manganese ions and a glutathione-dependent system for defense against nitric oxide which is under the control of a novel MerR-like transcriptional regulator. An understanding of the defenses against oxidative stress in N. gonorrhoeae and their regulation may provide new insights into the ways in which this bacterium survives challenges from polymorphonuclear leukocytes and urogenital epithelial cells.

Azurin of pathogenic Neisseria spp. is involved in defense against hydrogen peroxide and survival within cervical epithelial cells

Laz, a lipid-modified azurin of the human pathogens Neisseria gonorrhoeae and Neisseria meningitidis, is involved in defense against oxidative stress and copper toxicity; laz mutant strains are hypersensitive to hydrogen peroxide and copper. The N. gonorrhoeae laz mutant also has decreased survival in an ex vivo primary human ectocervical epithelial assay.