The ironclad truth: how in vivo transcriptomics and in vitro mechanistic studies shape our understanding of Neisseria gonorrhoeae gene regulation during mucosal infection

Transcriptomic signature of bacteria exposed to benzalkonium chloride

The COVID-19 pandemic has highlighted our reliance on biocides, the increasing prevalence of resistance to biocides is a risk to public health. Bacterial exposure to the biocide, benzalkonium chloride (BAC), resulted in a unique transcriptomic profile, characterised by both a short and long-term response. Differential gene expression was observed in four main areas: motility, membrane composition, proteostasis, and the stress response. A metabolism shift to protect the proteome and the stress response were prioritised suggesting these are main resistance mechanisms. Whereas "well-established" mechanisms, such as biofilm formation, were not found to be differentially expressed after exposure to BAC.

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.

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.

Integrated Bioinformatic Analyses and Immune Characterization of New Neisseria gonorrhoeae Vaccine Antigens Expressed during Natural Mucosal Infection

There is an increasingly severe trend of antibiotic-resistant Neisseria gonorrhoeae strains worldwide and new therapeutic strategies are needed against this sexually-transmitted pathogen. Despite the urgency, progress towards a gonococcal vaccine has been slowed by a scarcity of suitable antigens, lack of correlates of protection in humans and limited animal models of infection. N. gonorrhoeae gene expression levels in the natural human host does not reflect expression in vitro, further complicating in vitro-basedvaccine analysis platforms. We designed a novel candidate antigen selection strategy (CASS), based on a reverse vaccinology-like approach coupled with bioinformatics. We utilized the CASS to mine gonococcal proteins expressed during human mucosal infection, reported in our previous studies, and focused on a large pool of hypothetical proteins as an untapped source of potential new antigens. Via two discovery and analysis phases (DAP), we identified 36 targets predicted to be immunogenic, membrane-associated proteins conserved in N. gonorrhoeae and suitable for recombinant expression. Six initial candidates were produced and used to immunize mice. Characterization of the immune responses indicated cross-reactive antibodies and serum bactericidal activity against different N. gonorrhoeae strains. These results support the CASS as a tool for the discovery of new vaccine candidates.