Progress Toward a Gonococcal Vaccine: The Way Forward

Investigating the importance of selected surface-exposed loops in HpuB for hemoglobin binding and utilization by Neisseria gonorrhoeae

Neisseria gonorrhoeae is the etiological agent of the sexually transmitted infection gonorrhea. The pathogen is a global health challenge since no protective immunity results from infection, and far fewer treatment options are available with increasing antimicrobial resistance. With no efficacious vaccines, researchers are exploring new targets for vaccine development and innovative therapeutics. The outer membrane TonB-dependent transporters (TdTs) produced by N. gonorrhoeae are considered promising vaccine antigens as they are highly conserved and play crucial roles in overcoming nutritional immunity. One of these TdTs is part of the hemoglobin transport system comprised of HpuA and HpuB. This system allows N. gonorrhoeae to acquire iron from hemoglobin (hHb). In the current study, mutations in the hpuB gene were generated to better understand the structure-function relationships in HpuB. This study is one of the first to demonstrate that N. gonorrhoeae can bind to and utilize hemoglobin produced by animals other than humans. This study also determined that when HpuA is absent, mutations targeting extracellular loop 7 of HpuB led to defective hHb binding and utilization. However, when the lipoprotein HpuA is present, these loop 7 mutants recovered their ability to bind hHb, although the growth phenotype remained significantly impaired. Interestingly, loop 7 contains putative heme-binding motifs and a hypothetical α-helical region, both of which may be important for the use of hHb. Taken together, these results highlight the importance of loop 7 in the functionality of HpuB in binding hHb and extracting and internalizing iron.

Characterization of Neisseria gonorrhoeae colonization of macrophages under distinct polarization states and nutrients environment

Neisseria gonorrhoeae (Ng) is a uniquely adapted human pathogen and the etiological agent of gonorrhea, a sexually transmitted disease. Ng has developed numerous mechanisms to avoid and actively suppress innate and adaptive immune responses. Ng successfully colonizes and establishes topologically distinct colonies in human macrophages and avoids phagocytic killing. During colonization, Ng manipulates the actin cytoskeleton to invade and create an intracellular niche supportive of bacterial replication. The cellular reservoir(s) supporting bacterial replication and persistence in gonorrhea infections are poorly defined. The manner in which gonococci colonize macrophages points to this innate immune phagocyte as a strong candidate for a cellular niche during natural infection. Here we investigate whether nutrients availability and immunological polarization alter macrophage colonization by Ng. Differentiation of macrophages in pro-inflammatory (M1-like) and tolerogenic (M2-like) phenotypes prior to infection reveals that Ng can invade macrophages in all activation states, albeit with lower efficiency in M1-like macrophages. These results suggest that during natural infection, bacteria could invade and grow within macrophages regardless of the nutrients availability and the macrophage immune activation status.

In Vitro Bactericidal Activity of Biogenic Copper Oxide Nanoparticles for Neisseria gonorrhoeae with Enhanced Compatibility for Human Cells

Resistance to antibiotics and antimicrobial compounds is a significant problem for human and animal health globally. The development and introduction of new antimicrobial compounds are urgently needed, and copper oxide nanoparticles (CuO NPs) have found widespread application across various sectors including biomedicine, pharmacy, catalysis, cosmetics, and many others. What makes them particularly attractive is the possibility of their synthesis through biogenic routes. In this study, we synthesized biogenic green tea (GT, Camellia sinensis)-derived CuO NPs (GT CuO NPs) and examined their biophysical properties, in vitro toxicity for mammalian cells in culture, and then tested them against Neisseria gonorrhoeae, an exemplar Gram-negative bacterium from the World Health Organization's Priority Pathogen List. We compared our synthesized GT CuOP NPs with commercial CuO NPs (Com CuO NPs). Com CuO NPs were significantly more cytotoxic to mammalian cells (IC50 of 7.32 μg/mL) than GT CuO NPs (IC50 of 106.1 μg/mL). GT CuO NPs showed no significant increase in bax, bcl2, il6, and il1β mRNA expression from mammalian cells, whereas there were notable rises after treatment with Com CuO NPs. GT-CuO NPs required concentrations of 0.625 and 3.125 μg/mL to kill 50 and 100% of bacteria, respectively, whereas Com-CuO NPs needed concentrations of 15.625 and 30 μg/mL to kill 50 and 100% of bacteria, and the antibiotic ceftriaxone killed 50 and 100% with 3.125 and 30 μg/mL. Gonococci could be killed within 30 min of exposure to GT CuO NPs and the NPs could kill up to 107 within 1 h. In summary, this is the first report to our knowledge that describes the bioactivity of biogenic CuO NPs against N. gonorrhoeae. Our data suggest that biogenic nanoparticle synthesis has significant advantages over traditional chemical routes of synthesis and highlights the potential of GT-CuO NPs in addressing the challenges posed by multidrug-resistant Neisseria gonorrhoeae infections.

Addressing Sexually Transmitted Infections Due to Neisseria gonorrhoeae in the Present and Future

It was in the 1800s when the first public publications about the infection and treatment of gonorrhoea were released. However, the first prevention programmes were only published a hundred years later. In the 1940s, the concept of vaccination was introduced into clinical prevention programmes to address early sulphonamide resistance. Since then, tons of publications on Neisseria gonorrhoeae are undisputed, around 30,000 publications today. Currently, the situation seems to be just as it was in the last century, nothing has changed or improved. So, what are we doing wrong? And more importantly, what might we do? The review presented here aims to review the current situation regarding the resistance mechanisms, prevention programmes, treatments, and vaccines, with the challenge of better understanding this special pathogen. The authors have reviewed the last five years of advancements, knowledge, and perspectives for addressing the Neisseria gonorrhoeae issue, focusing on new therapeutic alternatives.

Current alternative therapies for treating drug-resistant Neisseria gonorrhoeae causing ophthalmia neonatorum

Ophthalmia neonatorum is a microbial contraction, damaging eyesight, occurring largely among neonates. Infants are particularly vulnerable to bacterial infections acquired during birth from infected mothers, especially from Neisseria gonorrhoeae and Chlamydia trachomatis. Over the decades, N. gonorrhoeae is alarmingly developing a resistance to most antibiotics currently prescribed. To counter this challenge, it is imperative to find potent and cost-effective therapeutic agents for prophylaxis and treatment, to which the N. gonorrhoeae cannot easily develop resistance. This review showcases alternate therapies such as antimicrobial-fatty acids, -peptides, -nano-formulations etc., currently evident against N. gonorrhoeae-mediated ophthalmia neonatorum, which remains a major cause of ocular morbidity, blindness and even death among neonates in developing countries.

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.

Characterization of Neisseria gonorrhoeae colonization of macrophages under distinct polarization states and nutrients environment

Neisseria gonorrhoeae (Ng) is a uniquely adapted human pathogen and the etiological agent of gonorrhea, a sexually transmitted disease. Ng has developed numerous mechanisms to avoid and actively suppress innate and adaptive immune responses. Ng successfully colonizes and establishes topologically distinct colonies in human macrophages and avoids phagocytic killing. During colonization, Ng manipulates the actin cytoskeleton to invade and create an intracellular niche supportive of bacterial replication. The cellular reservoir(s) supporting bacterial replication and persistence in gonorrhea infections are poorly defined. The manner in which gonococci colonize macrophages points to this innate immune phagocyte as a strong candidate for a cellular niche during natural infection. Here we investigate whether nutrients availability and immunological polarization alter macrophage colonization by Ng . Differentiation of macrophages in pro-inflammatory (M1-like) and tolerogenic (M2-like) phenotypes prior to infection reveals that Ng can invade macrophages in all activation states, albeit with lower efficiency in M1-like macrophages. These results suggest that during natural infection, bacteria could invade and grow within macrophages regardless of the nutrients availability and the macrophage immune activation status.

Computational structure-based approach to study chimeric antigens using a new protein scaffold displaying foreign epitopes

The identification and recombinant production of functional antigens and/or epitopes of pathogens represent a crucial step for the development of an effective protein-based vaccine. Many vaccine targets are outer membrane proteins anchored into the lipidic bilayer through an extended hydrophobic portion making their recombinant production challenging. Moreover, only the extracellular loops, and not the hydrophobic regions, are naturally exposed to the immune system. In this work, the Domain 3 (D3) from Group B Streptococcus (GBS) pilus 2a backbone protein has been identified and engineered to be used as a scaffold for the display of extracellular loops of two Neisseria gonorrhoeae membrane proteins (PorB.1b and OpaB). A computational structure-based approach has been applied to the design of both the scaffold and the model antigens. Once identified the best D3 engineerable site, several different chimeric D3 displaying PorB.1b and OpaB extracellular loops were produced as soluble proteins. Each molecule has been characterized in terms of solubility, stability, and ability to correctly display the foreign epitope. This antigen dissection strategy allowed the identification of most immunogenic extracellular loops of both PorB.1b and OpaB gonococcal antigens. The crystal structure of chimeric D3 displaying PorB.1b immunodominant loop has been obtained confirming that the engineerization did not alter the predicted native structure of this epitope. Taken together, the reported data suggest that D3 is a novel protein scaffold for epitope insertion and display, and a valid alternative to the production of whole membrane protein antigens. Finally, this work describes a generalized computational structure-based approach for the identification, design, and dissection of epitopes in target antigens through chimeric proteins.

Ameliorating Gonorrhea: Recent Therapeutic Adaptations and Scope to Improve its Prevailing Condition

BACKGROUND

Gonorrhea is a sexually transmitted infection (STI) caused by the bacteria Neisseria gonorrhoeae. According to recent research, the prevalence of gonorrhea has been increasing in many parts of the world, with some areas reporting high rates of antibiotic resistance. In the United States, the Centers for Disease Control and Prevention (CDC) reported that the number of reported gonorrhea cases increased by 56% between 2015 and 2019. Globally, the World Health Organization (WHO) estimated that there were 87 million new cases of gonorrhea in 2016, with the highest burden of infection in low- and middle-income countries. Research has also shown that gonorrhea is becoming increasingly resistant to conventional antibiotics, increasing the prevalence of gonorrhea. This raises concerns and challenges in disease management.

OBJECTIVES

The present review gives updated insight on the current state of the disease, challenges, and shortcomings of existing approaches along with the modern and alternative direction like vaccine development, its challenges, and scope to confront the existing state of drug resistance and increased rate of incidence. Alternative strategies like immunotherapy and phage therapy along with recent antibiotics researched for the treatment of gonorrhea.

CONCLUSION

The review provides a thorough insight into the current state of the disease and various available methods used currently and recommended by WHO. To overcome disease prevalence, various alternate therapies are coming into the limelight. However, scientists and researchers show a lack of interest in the drug development and research of gonorrhea, due to less commercial scope, lack of funding, and limited scope in the scientific scenario. These hurdles need to be overcome to meet the WHO vision of reducing gonorrhea by 90% by 2030. So, there is a need to optimize the drug therapy (optimizing dosing schedule, and precision monitoring) to reduce the chance of drug resistance. Also, there is a wide scope for drug and therapeutic system development.

Vaccine value profile for Neisseria gonorrhoeae

Neisseria gonorrhoeae infection (gonorrhoea) is a global public health challenge, causing substantial sexual and reproductive health consequences, such as infertility, pregnancy complications and increased acquisition or transmission of HIV. There is an urgency to controlling gonorrhoea because of increasing antimicrobial resistance to ceftriaxone, the last remaining treatment option, and the potential for gonorrhoea to become untreatable. No licensed gonococcal vaccine is available. Mounting observational evidence suggests that N. meningitidis serogroup B outer membrane vesicle-based vaccines may induce cross-protection against N. gonorrhoeae (estimated 30%-40% effectiveness using the 4CMenB vaccine). Clinical trials to determine the efficacy of the 4CMenB vaccine against N. gonorrhoeae are underway, as are Phase 1/2 studies of a new gonococcal-specific vaccine candidate. Ultimately, a gonococcal vaccine must be accessible, affordable and equitably dispensed, given that those most affected by gonorrhoea are also those who may be most disadvantaged in our societies, and most cases are in less-resourced settings. This vaccine value profile (VVP) provides a high level, holistic assessment of the current data to inform the potential public health, economic and societal value of pipeline vaccines. This was developed by a working group of subject matter experts from academia, non-profit organizations, public private partnerships and multi-lateral organizations. All contributors have extensive expertise on various elements of the N. gonorrhoeae VVP and collectively aimed to identify current research and knowledge gaps. The VVP was developed using published data obtained from peer-reviewed journals or reports.

Development of a Tag/Catcher-mediated capsid virus-like particle vaccine presenting the conserved Neisseria gonorrhoeae SliC antigen that blocks human lysozyme

Virus-like particles (VLPs) are promising nanotools for the development of subunit vaccines due to high immunogenicity and safety. Herein, we explored the versatile and effective Tag/Catcher-AP205 capsid VLP (cVLP) vaccine platform to address the urgent need for the development of an effective and safe vaccine against gonorrhea. The benefits of this clinically validated cVLP platform include its ability to facilitate unidirectional, high-density display of complex/full-length antigens through an effective split-protein Tag/Catcher conjugation system. To assess this modular approach for making cVLP vaccines, we used a conserved surface lipoprotein, SliC, that contributes to the Neisseria gonorrhoeae defense against human lysozyme, as a model antigen. This protein was genetically fused at the N- or C-terminus to the small peptide Tag enabling their conjugation to AP205 cVLP, displaying the complementary Catcher. We determined that SliC with the N-terminal SpyTag, N-SliC, retained lysozyme-blocking activity and could be displayed at high density on cVLPs without causing aggregation. In mice, the N-SliC-VLP vaccines, adjuvanted with AddaVax or CpG, induced significantly higher antibody titers compared to controls. In contrast, similar vaccine formulations containing monomeric SliC were non-immunogenic. Accordingly, sera from N-SliC-VLP-immunized mice also had significantly higher human complement-dependent serum bactericidal activity. Furthermore, the N-SliC-VLP vaccines administered subcutaneously with an intranasal boost elicited systemic and vaginal IgG and IgA, whereas subcutaneous delivery alone failed to induce vaginal IgA. The N-SliC-VLP with CpG (10 µg/dose) induced the most significant increase in total serum IgG and IgG3 titers, vaginal IgG and IgA, and bactericidal antibodies.

Investigating the importance of surface exposed loops in the gonococcal HpuB transporter for hemoglobin binding and utilization

Neisseria gonorrhoeae is the etiological agent of the sexually-transmitted infection gonorrhea and a global health challenge since no protective immunity results from infection and far fewer treatment options are available with increasing antimicrobial resistance. With no efficacious vaccines, researchers are exploring new targets for vaccine development and innovative therapeutics. The outer membrane TonB-dependent transporters (TdTs) produced by N. gonorrhoeae are considered promising antigen targets as they are highly conserved and play crucial roles in overcoming nutritional immunity. One of these TdTs, the hemoglobin transport system comprised of HpuA and HpuB, allows N. gonorrhoeae to acquire iron from hemoglobin (hHb). In the current study, mutations in the hpuB gene were generated to better understand the structure-function relationships in HpuB. This study is one of the first to demonstrate that N. gonorrhoeae can bind to and utilize hemoglobin produced by animals other than humans. This study also determined that when HpuA is absent, mutations targeting extracellular loop 7 of HpuB led to defective hHb binding and utilization. However, when the lipoprotein HpuA is present, these loop 7 mutants recovered their ability to bind hHB, although their growth phenotype remained significantly impaired. Interestingly, loop 7 contains putative heme binding motifs and a hypothetical α-helical region. Taken together, these results highlight the importance of loop 7 in the functionality of HpuB in binding hHb, and extracting and internalizing iron.

Bactericidal activity of esculetin is associated with impaired cell wall synthesis by targeting glutamate racemase of Neisseria gonorrhoeae

Neisseria gonorrhoeae (NG), the causative organism of gonorrhea, has been classified by the World Health Organization as 'Priority' two organism owing to its increased resistance to antibiotics and even failure of recommended dual therapy with ceftriaxone and azithromycin. As a result, the general and reproductive health of infected individuals is severely compromised. The imminent public health catastrophe of antimicrobial-resistant gonococci cannot be understated, as t he of severe complications and sequelae of infection are not only increasing but their treatment has also become more expensive. Tenacious attempts are underway to discover novel drug targets as well as new drugs to fight against NG. Therefore, a considerable number of phytochemicals have been tested for their remedial intercession via targeting bacterial proteins. The MurI gene encodes for an enzyme called glutamate racemase (MurI) that is primarily involved in peptidoglycan (PG) biosynthesis and is specific to the bacterial kingdom and hence can be exploited as a potential drug target for the treatment of bacterial diseases. Accordingly, diverse families of phytochemicals were screened in silico for their binding affinity with N. Gonorrhoeae MurI (NG-MurI) protein. Esculetin, one of the shortlisted compounds, was evaluated for its functional, structural, and anti-bacterial activity. Treatment with esculetin resulted in growth inhibition, cell wall damage, and altered permeability as revealed by fluorescence and electron microscopy. Furthermore, esculetin inhibited the racemization activity of recombinant, purified NG-MurI protein, one of the enzymes required for peptidoglycan biosynthesis. Our results suggest that esculetin could be further explored as a lead compound for developing new drug molecules against multidrug-resistant strains.

High-throughput bactericidal assays for monoclonal antibody screening against antimicrobial resistant Neisseria gonorrhoeae

Neisseria gonorrhoeae (gonococcus) is an obligate human pathogen and the etiological agent of the sexually transmitted disease gonorrhea. The rapid rise in gonococcal resistance to all currently available antimicrobials has become a significant public health burden and the need to develop novel therapeutic and prophylactic tools is now a global priority. While high-throughput screening methods allowed rapid discovery of extremely potent monoclonal antibodies (mAbs) against viral pathogens, the field of bacteriology suffers from the lack of assays that allow efficient screening of large panels of samples. To address this point, we developed luminescence-based (L-ABA) and resazurin-based (R-ABA) antibody bactericidal assays that measure N. gonorrhoeae metabolic activity as a proxy of bacterial viability. Both L-ABA and R-ABA are applicable on the large scale for the rapid identification of bactericidal antibodies and were validated by conventional methods. Implementation of these approaches will be instrumental to the development of new medications and vaccines against N. gonorrhoeae and other bacterial pathogens to support the fight against antimicrobial resistance.

Meningococcus B Vaccination Effectiveness Against Neisseria gonorrhoeae Infection in People Living With HIV: A Case-Control Study

BACKGROUND

We assessed the vaccination effectiveness (VE) of multicomponent meningococcal serogroup B (4CMenB) vaccine against gonorrhea among people living with HIV (PLWH) with a previous diagnosis of sexually transmitted infection.

METHODS

Unmatched case-control study on men who have sex with men living with HIV, in care at San Raffaele Scientific Institute, Milan, Italy, with gonorrhea, syphilis, chlamydia, or anal human papillomavirus between July 2016 (beginning of 4CMenB vaccination) and February 2021 (date of freezing). For the analysis, cases were people with ≥1 gonorrhea infection since July 2016, and controls were people with ≥1 syphilis, chlamydia, or anal human papillomavirus infection since July 2016. Logistic regression was used to provide the estimate of 4CMenB VE against gonorrhea.

RESULTS

Included people living with HIV were 1051 (103 cases, 948 controls); 349 of 1051 (33%) received 2 doses of 4CMenB vaccination. The median follow-up was 3.8 years (2.1-4.3 years). The unadjusted estimate for VE against gonorrhea was 42% (95% confidence interval, 6%-64%; P = 0.027). Logistic regression showed that VE against gonorrhea remained significant (44%; 95% confidence interval, 9%-65%; P = 0.020) after adjusting for some factors that might have a potential influence on VE or those with significant unbalanced distributions between cases and controls at univariable analysis.

CONCLUSIONS

4CMenB vaccination is associated with a lower risk of gonorrhea in the setting of men who have sex with men living with HIV with a previous sexually transmitted infection.

Microencapsulated IL-12 Drives Genital Tract Immune Responses to Intranasal Gonococcal Outer Membrane Vesicle Vaccine and Induces Resistance to Vaginal Infection with Diverse Strains of Neisseria gonorrhoeae

An experimental gonococcal vaccine consisting of outer membrane vesicles (OMVs) and microsphere (ms)-encapsulated interleukin-12 (IL-12 ms) induces Th1-driven immunity, with circulating and genital antibodies to Neisseria gonorrhoeae, after intravaginal (i.vag.) administration in female mice, and generates resistance to vaginal challenge infection. Because i.vag. administration is inapplicable to males and may not be acceptable to women, we determined whether intranasal (i.n.) administration would generate protective immunity against N. gonorrhoeae. Female and male mice were immunized i.n. with gonococcal OMVs plus IL-12 ms or blank microspheres (blank ms). Responses to i.n. immunization were similar to those with i.vag. immunization, with serum IgG, salivary IgA, and vaginal IgG and IgA antigonococcal antibodies induced when OMVs were administered with IL-12 ms. Male mice responded with serum IgG and salivary IgA antibodies similarly to female mice. Gamma interferon (IFN-γ) production by CD4⁺ T cells from iliac lymph nodes was elevated after i.n. or i.vag. immunization with OMVs plus IL-12 ms. Female mice immunized with OMVs plus IL-12 ms by either route resisted challenge with N. gonorrhoeae to an equal extent, and resistance generated by i.n. immunization extended to heterologous strains of N. gonorrhoeae. Detergent-extracted OMVs, which have diminished lipooligosaccharide, generated protective immunity to challenge similar to native OMVs. OMVs from mutant N. gonorrhoeae, in which genes for Rmp and LpxL1 were deleted to eliminate the induction of blocking antibodies against Rmp and diminish lipooligosaccharide endotoxicity, also generated resistance to challenge infection similar to wild-type OMVs when administered i.n. with IL-12 ms. IMPORTANCE We previously demonstrated that female mice can be immunized intravaginally with gonococcal outer membrane vesicles (OMVs) plus microsphere (ms)-encapsulated interleukin-12 (IL-12 ms) to induce antigonococcal antibodies and resistance to genital tract challenge with live Neisseria gonorrhoeae. However, this route of vaccination may be impractical for human vaccine development and is inapplicable to males. Because intranasal immunization has previously been shown to induce antibody responses in both male and female genital tracts, we have evaluated this route of immunization with gonococcal OMVs plus IL-12 ms. In addition, we have refined the composition of gonococcal OMVs to reduce the endotoxicity of lipooligosaccharide and to eliminate the membrane protein Rmp, which induces countereffective blocking antibodies. The resulting vaccine may be more suitable for ultimate translation to human application against the sexually transmitted infection gonorrhea, which is becoming increasingly resistant to treatment with antibiotics.

Estimating the population level impact of a gonococcal vaccine candidate: Predictions from a simple mathematical model

BACKGROUND

Neisseria gonorrhoeae cross-protection was suggested in a New Zealand meningitis B vaccine. We modeled the potential impact of similar vaccines on gonorrhea prevalence in heterosexuals in the United States.

METHODS

Our mathematical model incorporated infection, behavior, and vaccination dynamics. Approximate Bayesian Computation calibrated our model to US prevalence. Primary analyses assumed New Zealand vaccine characteristics: 30% efficacy and 2-year duration of protection. We estimated impact under two vaccine coverages (20%, 50%).

RESULTS

Reduction in gonorrhea prevalence ranged from 4.8 to 39.4%, depending on vaccine coverage. Vaccine impact was correlated with both size of the highly sexually active subpopulation and sexual mixing between high and low activity subpopulations.

CONCLUSIONS

A meningitis vaccine providing low efficacy cross-protection against gonorrhea acquisition and short duration of protection could result in a large reduction in gonorrhea prevalence in the United States. Potential dual protective effects can be considered when making vaccine recommendations.

Point Mutations in TbpA Abrogate Human Transferrin Binding in Neisseria gonorrhoeae

TonB-dependent transporters (TDTs) are essential proteins for metal acquisition, an important step in the growth and pathogenesis of many pathogens, including Neisseria gonorrhoeae, the causative agent of gonorrhea. There is currently no available vaccine for gonorrhea; TDTs are being investigated as vaccine candidates because they are highly conserved and expressed in vivo. Transferrin binding protein A (TbpA) is an essential virulence factor in the initiation of experimental infection in human males and functions by acquiring iron upon binding to host transferrin (human transferrin [hTf]). The loop 3 helix (L3H) is a helix finger that inserts into the hTf C-lobe and is required for hTf binding and subsequent iron acquisition. This study identified and characterized the first TbpA single-point substitutions resulting in significantly decreased hTf binding and iron acquisition, suggesting that the helix structure is more important than charge for hTf binding and utilization. The tbpA D355P ΔtbpB and tbpA A356P ΔtbpB mutants demonstrated significantly reduced hTf binding and impaired iron uptake from Fe-loaded hTf; however, only the tbpA A356P ΔtbpB mutant was able to grow when hTf was the sole source of iron. The expression of tbpB was able to restore function in all tbpA mutants. These results implicate both D355 and A356 in the key binding, extraction, and uptake functions of gonococcal TbpA.

G-quadruplexes in bacteria: insights into the regulatory roles and interacting proteins of non-canonical nucleic acid structures

G-quadruplexes (G4s) are highly stable, non-canonical DNA or RNA structures that can form in guanine-rich stretches of nucleic acids. G4-forming sequences have been found in all domains of life, and proteins that bind and/or resolve G4s have been discovered in both bacterial and eukaryotic organisms. G4s regulate a variety of cellular processes through inhibitory or stimulatory roles that depend upon their positions within genomes or transcripts. These include potential roles as impediments to genome replication, transcription, and translation or, in other contexts, as activators of genome stability, transcription, and recombination. This duality suggests that G4 sequences can aid cellular processes but that their presence can also be problematic. Despite their documented importance in bacterial species, G4s remain understudied in bacteria relative to eukaryotes. In this review, we highlight the roles of bacterial G4s by discussing their prevalence in bacterial genomes, the proteins that bind and unwind G4s in bacteria, and the processes regulated by bacterial G4s. We identify limitations in our current understanding of the functions of G4s in bacteria and describe new avenues for studying these remarkable nucleic acid structures.

Stealthy microbes: How Neisseria gonorrhoeae hijacks bulwarked iron during infection

Transition metals are essential for metalloprotein function among all domains of life. Humans utilize nutritional immunity to limit bacterial infections, employing metalloproteins such as hemoglobin, transferrin, and lactoferrin across a variety of physiological niches to sequester iron from invading bacteria. Consequently, some bacteria have evolved mechanisms to pirate the sequestered metals and thrive in these metal-restricted environments. Neisseria gonorrhoeae, the causative agent of the sexually transmitted infection gonorrhea, causes devastating disease worldwide and is an example of a bacterium capable of circumventing human nutritional immunity. Via production of specific outer-membrane metallotransporters, N. gonorrhoeae is capable of extracting iron directly from human innate immunity metalloproteins. This review focuses on the function and expression of each metalloprotein at gonococcal infection sites, as well as what is known about how the gonococcus accesses bound iron.

Mutagenesis of the Loop 3 α-Helix of Neisseria gonorrhoeae TdfJ Inhibits S100A7 Binding and Utilization

Neisseria gonorrhoeae causes the sexually transmitted infection (STI) gonorrhea, which afflicts over 80 million people each year. No vaccine is available to prevent gonorrhea. The pathogen alters the expression and antigenic presentation of key surface molecules, making the identification of suitable vaccine targets difficult. The human host utilizes metal-binding proteins to limit free essential transition metal ions available to invading pathogens, limiting their infective potential, a process called nutritional immunity. To overcome this, N. gonorrhoeae employs outer membrane TonB-dependent transporters (TdTs) that bind host nutritional immunity proteins and strip them of their metal cargo. The TdTs are well conserved, and some play key roles in establishing infections, making them promising vaccine targets. One TdT, TdfJ, recognizes human S100A7, a zinc-binding protein that inhibits the proliferation of other pathogens via zinc sequestration. N. gonorrhoeae uses TdfJ to strip and internalize zinc from S100A7. TdfJ contains a conserved α-helix finger in extracellular loop 3; a similar α-helix in loop 3 of another gonococcal TdT, TbpA, plays a critical role in the interaction between TbpA and human transferrin. Therefore, we hypothesized that the TdfJ loop 3 helix (L3H) participates in interactions with S100A7. We determined the affinity between wild-type TdfJ and S100A7 and then generated a series of mutations in the TdfJ L3H. Our study revealed that mutagenesis of key residues within the L3H reduced S100A7 binding and zinc piracy by the gonococcus, with profound effects seen with substitutions at residues K261 and R262. Taken together, these data suggest a key role for the TdfJ L3H in subverting host metal restriction.

Moenomycin is broadly active against multidrug-resistant Neisseria gonorrhoeae and clears an infection from a murine vaginal tract infection model

OBJECTIVES

Ceftriaxone therapy for gonorrhoea has become under increasing pressure due to waning susceptibility levels and emergence of high-level resistant strains such as the FC428 clone. Moenomycin was recently identified to display potent anti-gonococcal activity against some reference strains. Therefore, the aim of this study was to investigate moenomycin in vitro and in vivo antimicrobial activity.

METHODS

Moenomycin in vitro antimicrobial activity was investigated against 575 clinical isolates, including strains associated with the FC428 clone, using the agar dilution method. Moenomycin in vivo activity was investigated in a mouse vaginal tract gonococcal infection model.

RESULTS

The moenomycin MIC range for the strain collection was 0.004-0.06 mg/L, with a MIC50 of 0.016 mg/L and a MIC90 of 0.03 mg/L. The correlation between moenomycin and ceftriaxone susceptibility levels was poor (R = 0.13), while the fractional inhibitory concentration index (FICI) resulted in indifference for all tested strains. Therefore, development of cross-resistance between moenomycin and ceftriaxone is unlikely for N. gonorrhoeae. Determination of the moenomycin mode of activity against N. gonorrhoeae by time-kill assays showed that moenomycin is bactericidal, with over 104-fold inactivation observed after 4 h exposure. Finally, an intramuscular moenomycin dose of 10 mg/kg given on 2 consecutive days was able to clear a gonococcal infection in a mouse vaginal tract infection model within 1-3 days after the second dose, which was significantly faster than for mice treated with the vehicle control (P < 0.0001).

CONCLUSIONS

Moenomycin displays potent in vitro and in vivo antimicrobial activity against N. gonorrhoeae, warranting further exploration as alternative therapy.

Recent Progress Towards a Gonococcal Vaccine

Gonorrhea is a global health concern. Its etiological agent, Neisseria gonorrhoeae, rapidly acquires antimicrobial resistance and does not confer protective immunity as a consequence of infection. Attempts to generate an effective vaccine for gonorrhea have thus far been unsuccessful, as many structures on the bacterial envelope have the propensity to rapidly change, thus complicating recognition by the human immune system. In response to recent efforts from global health authorities to spur the efforts towards development of a vaccine, several new and promising steps have been made towards this goal, aided by advancements in computational epitope identification and prediction methods. Here, we provide a short review of recent progress towards a viable gonococcal vaccine, with a focus on antigen identification and characterization, and discuss a few of the tools that may be important in furthering these efforts.

Systemic and Mucosal Concentrations of Nine Cytokines Among Individuals with Neisseria gonorrhoeae infection in Nairobi Kenya

Introduction: The human-restricted sexually transmitted Neisseria gonorrhoeae (NG) has been shown to modulate the immune response against it and consequently the cytokines produced. The levels of cytokines in NG infection in the African population have not been well described. We aimed to quantify the systemic and mucosal cytokines in NG infection. Methods: This was a comparative cross-sectional study. Levels of nine cytokines (IL-1β, IL-2, IL-4, 1L-6, 1L-10, 1L-12p70, IL-17A, TNF-α and INF-γ) were measured from plasma and genital samples (urethral swabs in men and cervicovaginal lavage in women) from 61 Neisseria gonorrhoeae infected individuals seeking treatment for sexually transmitted infections (STIs) at Casino Health Centre in Nairobi, Kenya. A comparative group of 61 NG-uninfected individuals, seeking treatment at the same facility but with laboratory-confirmed negative Neisseria gonorrhoeae, Chlamydia trachomatis (CT), Mycoplasma genitalium (MG) and Trichomonas vaginalis(TV) was also included. The Mann-Whitney U test was used to compare the cytokine levels between NG-infected and uninfected individuals. Data was analyzed using STATA ver. 15.1. Results: Overall, systemic IL-6, TNF-α and IL-10 were elevated while genital IL-10 and TNF-α were lower in NG positive participants. On subgroup analysis by sex, the levels of genital IL-1β and IL-6 and systemic IL-6 were elevated in NG-infected men. None of the genital cytokines were elevated in NG-infected women, while all systemic cytokines, except INF-γ, were elevated in NG-infected women. Conclusions: Neisseria gonorrhoeae induced the production of different cytokines in men and women, with men having a pro-inflammatory genital response. These differences should be taken into consideration during development of various interventions e.g. vaccine development.

Risk of Disseminated Gonococcal Infections With Terminal Complement Blockade

Paroxysmal nocturnal hemoglobinuria is a clonal hematopoietic stem cell disorder resulting in complement-mediated hemolysis. Eculizumab, a monoclonal antibody against complement protein C5, has been shown to reduce both intravascular hemolysis and risk for thrombosis, and thereby improve the quality of life in these patients. While the infection risk from Neisseria meningitidis due to terminal complement blockade can be mitigated with appropriate immunizations and prophylactic antibiotics, these patients remain vulnerable to infections from Neisseria gonorrhoeae. Physicians and families should be aware of disseminated and severe gonococcal infections in patients receiving complement blockade, especially in this era of emerging cephalosporin and azithromycin resistance.

A Survey of Preclinical Studies Evaluating Nanoparticle-Based Vaccines Against Non-Viral Sexually Transmitted Infections

A worldwide estimate of over one million STIs are acquired daily and there is a desperate need for effective preventive as well as therapeutic measures to curtail this global health burden. Vaccines have been the most effective means for the control and potential eradication of infectious diseases; however, the development of vaccines against STIs has been a daunting task requiring extensive research for the development of safe and efficacious formulations. Nanoparticle-based vaccines represent a promising platform as they offer benefits such as targeted antigen presentation and delivery, co-localized antigen-adjuvant combinations for enhanced immunogenicity, and can be designed to be biologically inert. Here we discuss promising types of nanoparticles along with outcomes from nanoparticle-based vaccine preclinical studies against non-viral STIs including chlamydia, syphilis, gonorrhea, and recommendations for future nanoparticle-based vaccines against STIs.

Vaginal delivery of vaccines

Recent estimates suggest that one in two sexually active individuals will acquire a sexually transmitted infection by age 25, an alarming statistic that amounts to over 1 million new infections per day worldwide. Vaccination against STIs is highly desirable for alleviating this global burden of disease. Vaginal immunization is a promising strategy to combat transmission via the vaginal mucosa. The vagina is typically considered a poor inductive site for common correlates of adaptive immunity. However, emerging evidence suggests that immune tolerance may be overcome by precisely engineered vaccination schemes that orchestrate cell-mediated immunity and establish tissue resident memory immune cells. In this review, we will discuss the unique immunological milieu of the vaginal mucosa and our current understanding of correlates of pathogenesis and protection for several common STIs. We then present a summary of recent vaginal vaccine studies and explore the role that mucosal adjuvants and delivery systems play in enhancing protection according to requisite features of immunity. Finally, we offer perspectives on the challenges and future directions of vaginal vaccine delivery, discussing remaining physiological barriers and innovative vaccine formulations that may overcome them.

Infection with the US Neisseria meningitidis urethritis clade does not lower future risk of urethral gonorrhea

BACKGROUND

Cross-protective immunity between Neisseria meninigitidis (Nm) and Neisseria gonorrhoeae (Ng) may inform gonococcal vaccine development. Meningococcal serogroup B (MenB) outer membrane vesicle (OMV) vaccines confer modest protection against gonorrhea. However, whether urethral Nm infection protects against gonorrhea is unknown. We examined gonorrhea risk among men with US Nm urethritis clade (US_NmUC) infections.

METHODS

We conducted a retrospective cohort study of men with urethral US_NmUC (N=128) between January 2015 and April 2018. Using diagnosis date as the baseline visit, we examined Ng status at return visits to compute urethral Ng risk. We compared these data to three referent populations: men with urethral Ng (N=253), urethral chlamydia (Ct) (N=251), and no urethral Ng or Ct (N=255). We conducted sensitivity analyses to assess varied approaches to censoring, missing data, and anatomical site of infection. We also compared sequences of protein antigens in the OMV-based MenB-4C vaccine, US_NmUC, and Ng.

RESULTS

Participants were primarily Black (65%) and heterosexual (82%). Over follow-up, 91 men acquired urethral Ng. Men with urethral US_NmUC had similar Ng risk to men with prior urethral Ng (adjusted hazard ratio (AHR): 1∙27, 95% CI: 0∙65-2∙48). Men with urethral US_NmUC had insignificantly increased Ng risk compared to men with urethral Ct (AHR: 1∙51, 95% CI: 0∙79-2∙88), and significantly increased Ng risk compared to men without urethral Ng or Ct (AHR: 3∙55, 95% CI: 1∙27-9∙91). Most of the protein antigens analyzed shared high sequence similarity.

CONCLUSIONS

Urethral US_NmUC infection did not protect against gonorrhea despite substantial sequence similarities in shared protein antigens.

The potential utility of liposomes for Neisseria vaccines

INTRODUCTION

Species of the genus Neisseria are important global pathogens. Neisseria gonorrhoeae (gonococcus) causes the sexually transmitted disease gonorrhea and Neisseria meningitidis (meningococcus) causes meningitis and sepsis. Liposomes are self-assembled spheres of phospholipid bilayers enclosing a central aqueous space, and they have attracted much interest and use as a delivery vehicle for Neisseria vaccine antigens.

AREAS COVERED

A brief background on Neisseria infections and the success of licensed meningococcal vaccines are provided. The absence of a gonococcal vaccine is highlighted. The use of liposomes for delivering Neisseria antigens and adjuvants, for the purposes of generating specific immune responses, is reviewed. The use of other lipid-based systems for antigen and adjuvant delivery is examined briefly.

EXPERT OPINION

With renewed interest in developing a gonococcal vaccine, liposomes remain an attractive option for delivering antigens. The discipline of nanotechnology provides additional nanoparticle-based options for gonococcal vaccine development. Future work would be needed to tailor the composition of liposomes and other nanoparticles to the specific vaccine antigen(s), in order to generate optimal anti-gonococcal immune responses. The potential use of liposomes and other nanoparticles to deliver anti-gonococcal compounds to treat infections also should be explored further.

Recent advances in understanding and combatting Neisseria gonorrhoeae: a genomic perspective

The sexually transmitted infection (STI) gonorrhoea remains a major global public health concern. The World Health Organization (WHO) estimates that 87 million new cases in individuals who were 15 to 49 years of age occurred in 2016. The growing number of gonorrhoea cases is concerning given the rise in gonococci developing antimicrobial resistance (AMR). Therefore, a global action plan is needed to facilitate surveillance. Indeed, the WHO has made surveillance leading to the elimination of STIs (including gonorrhoea) a global health priority. The availability of whole genome sequence data offers new opportunities to combat gonorrhoea. This can be through (i) enhanced surveillance of the global prevalence of AMR, (ii) improved understanding of the population biology of the gonococcus, and (iii) opportunities to mine sequence data in the search for vaccine candidates. Here, we review the current status in Neisseria gonorrhoeae genomics. In particular, we explore how genomics continues to advance our understanding of this complex pathogen.

Priorities for sexually transmitted infection vaccine research and development: Results from a survey of global leaders and representatives

Objective

To determine the sexually transmitted infection (STI) vaccine research priorities of global leaders in STI vaccine research, development, and service provision.

Methods

Global representatives attending the STI Vaccines: Opportunities for Research, Development, and Implementation symposium preceding the STI & HIV World Congress in 2019 were invited to complete an electronic survey. We asked participants to rank items by importance/priority for STI vaccine development for the following areas of focus: specific STIs (gonorrhea, chlamydia, syphilis, herpes, and trichomoniasis), broad research domains (basic science, funding, communication, program planning, and vaccine hesitancy), and specific research activities related to these domains. We calculated weighted value scores based on the ranking (e.g., first, second, third) and the total number of responses in order to produce a ranked list of the priorities.

Results

A total of 46 out of 97 (44%) symposium attendees responded to the survey. Gonorrhea was identified as the STI that should be prioritized for vaccine development, followed by syphilis with weighted value scores of 3.82 and 3.37, respectively, out of a maximum of five. Basic science (and vaccine development) was the domain ranked with the highest priority with a weighted value score of 4.78 out of six. Research activities related to basic science and vaccine development (including pre-clinical and clinical trials, and surveillance measures) and increased funding opportunities were the most highly ranked activities in the “STI vaccine development” and “research domains and activities” categories.

Conclusion

Global leaders in attendance at the STI Vaccines symposium prioritized continued scientific work in vaccine development and program planning. Gonorrhea was identified as the highest priority infection, followed by syphilis.

Immune Responses to Neisseria gonorrhoeae: Challenges and Opportunities With Respect to Pelvic Inflammatory Disease

Pelvic inflammatory disease and infertility frequently develop after female genital tract infection with Neisseria gonorrhoeae, but determining their etiology from among various possibilities presents difficulties. Exploitation of serology to identify the causative agent is complicated by numerous factors, and no immunological test currently exists to determine unequivocally whether an individual currently is, or has been, infected with N. gonorrhoeae. The extensive antigenic variability of N. gonorrhoeae and its expression of antigens shared with other Neisseria species commonly carried in humans render problematic an assay that is specific for all gonococcal strains. However, novel conserved gonococcal antigens identified for potential vaccines may find additional application in diagnostic assays. N. gonorrhoeae also interferes with the adaptive immune response, and antibody responses to uncomplicated infection are usually weak. Elucidating the mechanisms whereby N. gonorrhoeae manipulates the human immune system may lead to improved understanding of the pathogenesis of pelvic inflammatory disease and infertility.

Vaccine Candidates for the Control and Prevention of the Sexually Transmitted Disease Gonorrhea

The World Health Organization (WHO) has placed N. gonorrhoeae on the global priority list of antimicrobial resistant pathogens and is urgently seeking the development of new intervention strategies. N. gonorrhoeae causes 86.9 million cases globally per annum. The effects of gonococcal disease are seen predominantly in women and children and especially in the Australian Indigenous community. While economic modelling suggests that this infection alone may directly cost the USA health care system USD 11.0–20.6 billion, indirect costs associated with adverse disease and pregnancy outcomes, disease prevention, and productivity loss, mean that the overall effect of the disease is far greater still. In this review, we summate the current progress towards the development of a gonorrhea vaccine and describe the clinical trials being undertaken in Australia to assess the efficacy of the current formulation of Bexsero^® in controlling disease.

Challenges and Controversies Concerning Neisseria gonorrhoeae-Neutrophil Interactions in Pathogenesis

The bacterium Neisseria gonorrhoeae (Ngo) is the main cause of the sexually transmitted infection gonorrhea. The global incidence of 87 million new Ngo infections each year, rising infection rates, and the emergence of Ngo strains that are resistant to all clinically recommended antibiotics have raised the specter of untreatable infections (M. Unemo, H. S. Seifert, E. W. Hook, III, S. Hawkes, et al., Nat Rev Dis Primers 5:79, 2019, https://doi.org/10.1038/s41572-019-0128-6). Given their abundance in symptomatic disease, neutrophils are central to both Ngo infection and consequent damage to host tissues. This article highlights present knowledge and the main open questions about Ngo-neutrophil interactions in immunity versus disease pathogenesis.

A community-driven resource for genomic epidemiology and antimicrobial resistance prediction of Neisseria gonorrhoeae at Pathogenwatch

BACKGROUND

Antimicrobial-resistant (AMR) Neisseria gonorrhoeae is an urgent threat to public health, as strains resistant to at least one of the two last-line antibiotics used in empiric therapy of gonorrhoea, ceftriaxone and azithromycin, have spread internationally. Whole genome sequencing (WGS) data can be used to identify new AMR clones and transmission networks and inform the development of point-of-care tests for antimicrobial susceptibility, novel antimicrobials and vaccines. Community-driven tools that provide an easy access to and analysis of genomic and epidemiological data is the way forward for public health surveillance.

METHODS

Here we present a public health-focussed scheme for genomic epidemiology of N. gonorrhoeae at Pathogenwatch ( https://pathogen.watch/ngonorrhoeae ). An international advisory group of experts in epidemiology, public health, genetics and genomics of N. gonorrhoeae was convened to inform on the utility of current and future analytics in the platform. We implement backwards compatibility with MLST, NG-MAST and NG-STAR typing schemes as well as an exhaustive library of genetic AMR determinants linked to a genotypic prediction of resistance to eight antibiotics. A collection of over 12,000 N. gonorrhoeae genome sequences from public archives has been quality-checked, assembled and made public together with available metadata for contextualization.

RESULTS

AMR prediction from genome data revealed specificity values over 99% for azithromycin, ciprofloxacin and ceftriaxone and sensitivity values around 99% for benzylpenicillin and tetracycline. A case study using the Pathogenwatch collection of N. gonorrhoeae public genomes showed the global expansion of an azithromycin-resistant lineage carrying a mosaic mtr over at least the last 10 years, emphasising the power of Pathogenwatch to explore and evaluate genomic epidemiology questions of public health concern.

CONCLUSIONS

The N. gonorrhoeae scheme in Pathogenwatch provides customised bioinformatic pipelines guided by expert opinion that can be adapted to public health agencies and departments with little expertise in bioinformatics and lower-resourced settings with internet connection but limited computational infrastructure. The advisory group will assess and identify ongoing public health needs in the field of gonorrhoea, particularly regarding gonococcal AMR, in order to further enhance utility with modified or new analytic methods.

Epidemiological and Clinical Observations of Gonococcal Infections in Women and Prevention Strategies

Neisseria gonorrhoeae is rapidly developing antimicrobial resistance. There is an urgent need for an effective gonococcal vaccine. In this study we examined epidemiological and clinical factors associated with gonorrhea in a cohort of women exposed to men with gonococcal urethritis attending the National Center for STD Control clinic in Nanjing, China, to understand the natural history and the risk factors for gonorrhea in this vulnerable population. This analysis will help identify the best target populations for vaccination, which is essential information for the development of vaccine strategies. We observed that 75% of the women in our cohort yielded a N. gonorrhoeae positive culture (infected women) and reported multiple sexual exposures to their infected partner. Infected women were younger than exposed but uninfected women. Contrary to the general belief that gonorrhea is asymptomatic in most women, 68% of the infected women acknowledged symptoms during their STD clinic visit, and overt inflammatory responses were detected upon medical examination in 88% of subjects. Other sexually transmitted infections were detected in 85% of subjects. This study confirmed that N. gonorrhoeae infections are underdiagnosed in women and, consequentially, untreated. Thus, our analysis reinforces the need to establish strategies for gonococcal prevention through the determination of the target population for a gonococcal vaccine.

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.

The serogroup B meningococcal outer membrane vesicle-based vaccine 4CMenB induces cross-species protection against Neisseria gonorrhoeae

There is a pressing need for a gonorrhea vaccine due to the high disease burden associated with gonococcal infections globally and the rapid evolution of antibiotic resistance in Neisseria gonorrhoeae (Ng). Current gonorrhea vaccine research is in the stages of antigen discovery and the identification of protective immune responses, and no vaccine has been tested in clinical trials in over 30 years. Recently, however, it was reported in a retrospective case-control study that vaccination of humans with a serogroup B Neisseria meningitidis (Nm) outer membrane vesicle (OMV) vaccine (MeNZB) was associated with reduced rates of gonorrhea. Here we directly tested the hypothesis that Nm OMVs induce cross-protection against gonorrhea in a well-characterized female mouse model of Ng genital tract infection. We found that immunization with the licensed Nm OMV-based vaccine 4CMenB (Bexsero) significantly accelerated clearance and reduced the Ng bacterial burden compared to administration of alum or PBS. Serum IgG and vaginal IgA and IgG that cross-reacted with Ng OMVs were induced by 4CMenB vaccination by either the subcutaneous or intraperitoneal routes. Antibodies from vaccinated mice recognized several Ng surface proteins, including PilQ, BamA, MtrE, NHBA (known to be recognized by humans), PorB, and Opa. Immune sera from both mice and humans recognized Ng PilQ and several proteins of similar apparent molecular weight, but MtrE was only recognized by mouse serum. Pooled sera from 4CMenB-immunized mice showed a 4-fold increase in serum bactericidal50 titers against the challenge strain; in contrast, no significant difference in bactericidal activity was detected when sera from 4CMenB-immunized and unimmunized subjects were compared. Our findings directly support epidemiological evidence that Nm OMVs confer cross-species protection against gonorrhea, and implicate several Ng surface antigens as potentially protective targets. Additionally, this study further defines the usefulness of murine infection model as a relevant experimental system for gonorrhea vaccine development.

Neisseria gonorrhoeae NGO2105 Is an Autotransporter Protein Involved in Adhesion to Human Cervical Epithelial Cells and in vivo Colonization

Autotransporters are important virulence factors in the outer membrane of gram-negative bacteria. Although several autotransporters have been identified in Neisseria meningitidis, only IgA1 protease has been identified in Neisseria gonorrhoeae. A sequence analysis showed a marked difference in the distribution of autotransporters between the two strains. It has been speculated that only two autotransporters, the IgA1 protease and the NGO2105 protein, might be encoded by N. gonorrhoeae. Here, we describe the identification of NGO2105, a new autotransporter in N. gonorrhoeae. A sequence alignment showed that NGO2105 is highly similar to the adhesion and penetration protein (App) in N. meningitidis. We found that NGO2105 is exported to the outer membrane, cleaved and released into the culture supernatant by endogenous serine protease activity in N. gonorrhoeae and E. coli. The site-directed mutagenesis of S267A in the predicted enzyme catalytic triad abolished autoproteolytic cleavage to allow secretion. The NGO2105 β-barrel shows the ability to translocate the heterologous Hbp passenger domain. NGO2105 is involved in gonococcal adherence to and invasion into human cervical epithelial cells. Furthermore, antibodies raised against NGO2105 are able to block gonococcal adherence to human cervical epithelial cells. The Δngo2105 mutant and anti-NGO2105 antiserum significantly attenuated the colonization of N. gonorrhoeae in mice. Collectively, our results suggest that the newly identified serine protease autotransporter NGO2105 represents a novel virulence factor of gonococcus and a potential vaccine target.

Gonococcal vaccines: Public health value and preferred product characteristics; report of a WHO global stakeholder consultation, January 2019

Renewed interest in developing vaccines against Neisseria gonorrhoeae has been sparked by the increasing threat of gonococcal antimicrobial resistance (AMR) and growing optimism that gonococcal vaccines are biologically feasible. Evidence suggests serogroup B Neisseria meningitidis vaccines might provide some cross-protection against N. gonorrhoeae, and new gonococcal vaccine candidates based on several approaches are currently in preclinical development. To further stimulate investment and accelerate development of gonococcal vaccines, greater understanding is needed regarding the overall value that gonococcal vaccines might have in addressing public health and societal goals in low-, middle-, and high-income country contexts and how future gonococcal vaccines might be accepted and used, if available. In January 2019, the World Health Organization (WHO) convened a multidisciplinary international group of experts to lay the groundwork for understanding the potential health, economic, and societal value of gonococcal vaccines and their likely acceptance and use, and for developing gonococcal vaccine preferred product characteristics (PPCs). WHO PPCs describe preferences for vaccine attributes that would help optimize vaccine value and use in meeting the global public health need. This paper describes the main discussion points and conclusions from the January 2019 meeting of experts. Participants emphasized the need for vaccines to control N. gonorrhoeae infections with the ultimate goals of preventing adverse sexual and reproductive health outcomes (e.g., infertility) and reducing the impact of gonococcal AMR. Meeting participants also discussed important PPC considerations (e.g., vaccine indications, target populations, and potential immunization strategies) and highlighted crucial research and data needs for guiding the value assessment and PPCs for gonococcal vaccines and advancing gonococcal vaccine development.

Antimicrobial resistance in sexually transmitted infections

RATIONALE FOR REVIEW

International travel facilitates the spread of drug-resistant infections, including sexually transmitted infections (STIs). In 2016, the World Health Organization highlighted the global burden of 'curable' STIs, estimating 376 million new infections of gonorrhoea, chlamydia, syphilis and trichomoniasis annually, with considerable geographic variation in both the burden of disease and prevalence of resistance. Travelers' risk of contracting and transmitting drug-resistant STIs depends in part on their geographic exposure. In this review, we describe the epidemiology of antimicrobial resistance (AMR) and the management of these four common STIs and Mycoplasma genitalium, an increasingly recognized cause of non-gonococcal urethritis.

KEY FINDINGS

Multi-drug and extensively drug resistant gonorrhoea strains have been associated with international spread, particularly in travelers returning from Southeast Asia. Chlamydia is the most common bacterial STI worldwide. Although in vitro resistance has been reported, surveillance data suggest that clinically significant resistance to macrolides and tetracyclines is rare. Macrolide resistance in syphilis is now endemic in much of the world but there is no documented penicillin resistance, which remains first-line therapy. Trichomoniasis is the most common non-viral STI worldwide. Although clinical failure after treatment occurs, resistance to metronidazole is thought to be uncommon. Mycoplasma genitalium exhibits intrinsic resistance to many antibiotics, and the prevalence of resistance to both first- and second-line regimens (macrolides and fluoroquinolones) is increasing worldwide, with limited alternative therapeutic options.

RECOMMENDATIONS

International travelers are at risk for acquiring resistant STIs with limited therapeutic options. Improved diagnostics are urgently needed to improve AMR surveillance and the management of infected patients. As no vaccinations are currently available for these STIs, and pre-exposure prophylaxis is an area of active study with limited data, condom use is critical for prevention. Travel medicine providers should incorporate STI risk reduction counselling, with an emphasis on condom use, into the routine pre-travel consultation.