Pharmacokinetic Data Are Predictive of In Vivo Efficacy for Cefixime and Ceftriaxone against Susceptible and Resistant Neisseria gonorrhoeae Strains in the Gonorrhea Mouse Model

Pharmacodynamic evaluation of ceftriaxone single-dose therapy (0.125-1 g) to eradicate ceftriaxone-susceptible and ceftriaxone-resistant Neisseria gonorrhoeae strains in a hollow fibre infection model for gonorrhoea

BACKGROUND

Antimicrobial resistance in Neisseria gonorrhoeae is threatening the gonorrhoea treatment, and optimizations of the current ceftriaxone-treatment regimens are crucial. We evaluated the pharmacodynamics of ceftriaxone single-dose therapy (0.125-1 g) against ceftriaxone-susceptible and ceftriaxone-resistant gonococcal strains, based on EUCAST ceftriaxone-resistance breakpoint (MIC > 0.125 mg/L), in our hollow fibre infection model (HFIM) for gonorrhoea.

METHODS

Gonococcal strains examined were WHO F (ceftriaxone-susceptible, MIC < 0.002 mg/L), R (ceftriaxone-resistant, MIC = 0.5 mg/L), Z (ceftriaxone-resistant, MIC = 0.5 mg/L) and X (ceftriaxone-resistant, MIC = 2 mg/L). Dose-range HFIM 7 day experiments simulating ceftriaxone 0.125-1 g single-dose intramuscular regimens were conducted.

RESULTS

Ceftriaxone 0.125-1 g single-dose treatments rapidly eradicated WHO F (wild-type ceftriaxone MIC). Ceftriaxone 0.5 and 1 g treatments, based on ceftriaxone human plasma pharmacokinetic parameters, eradicated most ceftriaxone-resistant gonococcal strains (WHO R and Z), but ceftriaxone 0.5 g failed to eradicate WHO X (high-level ceftriaxone resistance). When simulating oropharyngeal gonorrhoea, ceftriaxone 0.5 g failed to eradicate all the ceftriaxone-resistant strains, while ceftriaxone 1 g eradicated WHO R and Z (low-level ceftriaxone resistance) but failed to eradicate WHO X (high-level ceftriaxone resistance). No ceftriaxone-resistant mutants were selected using any ceftriaxone treatments.

CONCLUSIONS

Ceftriaxone 1 g single-dose intramuscularly cure most of the anogenital and oropharyngeal gonorrhoea cases caused by the currently internationally spreading ceftriaxone-resistant gonococcal strains, which should be further confirmed clinically. A ceftriaxone 1 g dose (±azithromycin 2 g) should be recommended for first-line empiric gonorrhoea treatment. This will buy countries some time until novel antimicrobials are licensed. Using ceftriaxone 1 g gonorrhoea treatment, the EUCAST ceftriaxone-resistance breakpoint is too low.

2023 Korean Association of Urogenital Tract Infection and Inflammation guidelines for gonococcal infection

The incidence of gonorrhea has increased significantly in recent years in the United States, especially among sexually active twenty-year-olds. Although the incidence of gonorrhea has decreased in Korea since the early 2000s, it is still common among people in their twenties. Nucleic acid amplification test (NAAT) is the most sensitive diagnostic test for detecting gonococcal infection. Gram-staining is a simple and useful laboratory test for diagnosing symptomatic male gonococcal urethritis. Although bacterial culture can be used to detect antimicrobial susceptibility, its sensitivity is lower than that of NAAT. Treatment for uncomplicated gonorrhea infection is a single intramuscular injection of ceftriaxone 500 mg. Doxycycline (100 mg twice daily for 7 days) is added if there is a possibility of co-infection with chlamydia. If ceftriaxone is difficult to use, spectinomycin 2 g can be injected intramuscularly in Korea. Patients with gonorrhea should have repeated examinations within three months at the exposure site because of a high risk of re-infection. A person diagnosed with gonorrhea should discuss the nature of the infection, the importance of informing partners, when sexual activity can resume, and how to reduce the risk of sexually transmitted infections.

Treatment of bacterial sexually transmitted infections in Europe: gonorrhoea, Mycoplasma genitalium, and syphilis

This review explores the therapeutic challenges of sexually transmitted infections (STI) in Europe, which include increasing antimicrobial resistance and limited progress in drug discovery. We primarily focus on gonorrhoea, Mycoplasma genitalium, and syphilis infections. For gonorrhoea with escalating resistance rates we explore the possibility of combining ceftriaxone with another antibiotic or using alternative antibiotics to mitigate resistance emergence, and we provide insights on the ongoing evaluation of new antimicrobials, like gepotidacin and zoliflodacin. In the case of M. genitalium, which exhibits high resistance rates to first and second-line treatments, we emphasize the importance of resistance-guided therapy in regions with elevated resistance levels, and highlight the limited alternative options, such as pristinamycin and minocycline. Furthermore, we address the challenges posed by syphilis, where the primary treatment consists of penicillin or doxycycline, with challenges arising in neurosyphilis, allergy, pregnancy, and supply shortages and discuss the ongoing evaluation of alternative antimicrobials (e.g., ceftriaxone, cefixime, linezolid). Our findings identify priority actions and provide concrete solutions for long-term effective management of STIs and antimicrobial resistance mitigation.

Gonococcal microparticle vaccine in dissolving microneedles induced immunity and enhanced bacterial clearance in infected mice

There is an alarming rise in the number of gonorrhea cases worldwide. Neisseria gonorrhoeae, the bacteria that causes gonorrhea infection, has gradually developed antimicrobial resistance over the years. To date, there is no licensed vaccine for gonorrhea. This study investigates the in vivo immunogenicity of a whole-cell inactivated gonococci in a microparticle formulation (Gc-MP) along with adjuvant microparticles (Alhydrogel®- Alum MP and AddaVax™ MP) delivered transdermally using dissolving microneedles (MN). The proposed vaccine formulation (Gc-MP + Alum MP + AddaVax™ MP) was assessed for induction of humoral, cellular, and protective immune responses in vivo. Our results show the induction of significant gonococcal-specific serum IgG, IgG1, IgG2a, and vaginal mucosal IgA antibodies in mice immunized with Gc-MP + Alum MP + AddaVax™ MP and Gc-MP when compared to the control groups receiving blank MN or no treatment. The serum bactericidal assay revealed that the antibodies generated in mice after immunization with Gc-MP + Alum MP + AddaVax™ MP were bactericidal towards live Neisseria gonorrhoeae. Gc-MP + Alum MP + AddaVax™ MP and Gc-MP-immunized mice showed enhanced clearance rate of gonococcal bacterial infection post challenge. In contrast, the control groups did not begin to clear the infection until day 10. In addition, the mice which received Gc-MP + Alum MP + AddaVax™ MP showed enhanced expression of cellular immunity markers CD4 and CD8 on the surface of T cells in the spleen and lymph nodes. Taken together, the data shows that microneedle immunization with whole-cell inactivated gonococci MP in mice induced humoral, cellular, and protective immunity against gonococcal infection.

Vertebrate and Invertebrate Animal and New In Vitro Models for Studying Neisseria Biology

The history of Neisseria research has involved the use of a wide variety of vertebrate and invertebrate animal models, from insects to humans. In this review, we itemise these models and describe how they have made significant contributions to understanding the pathophysiology of Neisseria infections and to the development and testing of vaccines and antimicrobials. We also look ahead, briefly, to their potential replacement by complex in vitro cellular models.

Sorangicin A Is Active against Chlamydia in Cell Culture, Explanted Fallopian Tubes, and Topical In Vivo Treatment

Current treatment of Chlamydia trachomatis using doxycycline and azithromycin introduces detrimental side effects on the host's microbiota. As a potential alternative treatment, the myxobacterial natural product sorangicin A (SorA) blocks the bacterial RNA polymerase. In this study we analyzed the effectiveness of SorA against C. trachomatis in cell culture, and explanted fallopian tubes and systemic and local treatment in mice, providing also pharmacokinetic data on SorA. Potential side effects of SorA on the vaginal and gut microbiome were assessed in mice and against human-derived Lactobacillus species. SorA showed minimal inhibitory concentrations of 80 ng/mL (normoxia) to 120 ng/mL (hypoxia) against C. trachomatis in vitro and was eradicating C. trachomatis at a concentration of 1 µg/mL from fallopian tubes. In vivo, SorA reduced chlamydial shedding by more than 100-fold within the first days of infection by topical application corresponding with vaginal detection of SorA only upon topical treatment, but not after systemic application. SorA changed gut microbial composition during intraperitoneal application only and did neither alter the vaginal microbiota in mice nor affect growth of human-derived lactobacilli. Additional dose escalations and/or pharmaceutical modifications will be needed to optimize application of SorA and to reach sufficient anti-chlamydial activity in vivo.

Dose selection for a phase III study evaluating gepotidacin (GSK2140944) in the treatment of uncomplicated urogenital gonorrhoea

BACKGROUND

Gepotidacin is a novel, first-in-class triazaacenaphthylene antibiotic that inhibits bacterial DNA replication by a distinct mechanism of action and is active against most strains of Neisseria gonorrhoeae (N. gonorrhoeae). Phase II data suggested higher exposures were needed for efficacy and to suppress resistance development. A translational approach using in vitro pharmacokinetic/pharmacodynamic (PK/PD) and clinical data was used to select a gepotidacin dose for a phase III study. In this narrative review of previously shown data, we summarise how a translational approach based on in vitro PK/PD and population PK modelling and simulation data was undertaken to select a dosing regimen for the ongoing phase III gepotidacin study in participants with uncomplicated urogenital gonorrhoea.

METHODS

For dose selection, prior in vitro minimum inhibitory concentrations (MICs) and PK/PD data were available. PK modelling was conducted to determine a dose that would limit plasma concentrations to less than 14 µg/mL (as concentrations above this are associated with QT prolongation and effects associated with acetylcholinesterase inhibition) while maintaining ≥90% probability of target attainment (PTA) for efficacy and resistance suppression against N. gonorrhoeae isolates with gepotidacin MICs ≤1 µg/mL.

RESULTS

Two 3000 mg gepotidacin doses, administered 10-12 hours apart, resulted in PTA of ≥97.5% and ≥91.7% for gepotidacin MICs ≤1 µg/mL for the ratio of the area under the free drug plasma concentration-time curve over 24 hours to the MIC (fAUC_0-24/MIC) efficacy, and resistance suppression targets of 40 and 46, respectively, but limited the occurrence of maximum plasma concentrations ≥14 µg/mL.

CONCLUSIONS

Two gepotidacin 3000 mg oral doses 10-12 hours apart provide ~2-fold higher systemic exposures, increase efficacy for higher gepotidacin MIC N. gonorrhoeae isolates, reduce resistance potential and limit plasma concentrations of potential safety concern, compared with higher doses.

Colonization efficiency of multidrug-resistant Neisseria gonorrhoeae in a female mouse model

The rapid occurrence of gonococcal resistance to all classes of antibiotics could lead to untreatable gonorrhea. Thus, development of novel anti-Neisseria gonorrhoeae drugs is urgently needed. Neisseria gonorrhoeae FA1090 is the most used in gonococcal infection mouse models because of its natural resistance to streptomycin. Streptomycin inhibits the urogenital commensal flora that permits gonococcal colonization. However, this strain is drug-susceptible and cannot be used to investigate the efficacy of novel agents against multidrug-resistant N. gonorrhoeae. Hence, to test the in vivo efficacy of new therapeutics against N. gonorrhoeae resistant to the frontline antibiotics, azithromycin, or ceftriaxone, we constructed streptomycin-resistant mutants of N. gonorrhoeae CDC-181 (azithromycin-resistant) and WHO-X (ceftriaxone-resistant). We identified the inoculum size needed to successfully colonize mice. Both mutants, CDC-181-rpsLA128G and WHO-X-rpsLA128G, colonized the genital tract of mice for 14 days with 100% colonization observed for at least 7 days. CDC-181-rpsLA128G demonstrated better colonization of the murine genital tract compared to WHO-X-rpsLA128G. Lower inoculum of WHO-X-rpsLA128G (105 and 106 CFU) colonized mice better than higher inoculum. Overall, our results indicate that CDC-181-rpsLA128G and WHO-X-rpsLA128G can colonize the lower genital tract of mice and are suitable to be used in mouse models to investigate the efficacy of antigonococcal agents.

A Novel Oral GyrB/ParE Dual Binding Inhibitor Effective against Multidrug-Resistant Neisseria gonorrhoeae and Other High-Threat Pathogens

Drug-resistant Neisseria gonorrhoeae is a serious global health concern. New drugs are needed that can overcome existing drug resistance and limit the development of new resistances. Here, we describe the small molecule tricyclic pyrimidoindole JSF-2414 [8-(6-fluoro-8-(methylamino)-2-((2-methylpyrimidin-5-yl)oxy)-9H-pyrimido[4,5-b]indol-4-yl)-2-oxa-8-azaspiro[4.5]decan-3-yl)methanol], which was developed to target both ATP-binding regions of DNA gyrase (GyrB) and topoisomerase (ParE). JSF-2414 displays potent activity against N. gonorrhoeae, including drug-resistant strains. A phosphate pro-drug, JSF-2659, was developed to facilitate oral dosing. In two different animal models of Neisseria gonorrhoeae vaginal infection, JSF-2659 was highly efficacious in reducing microbial burdens to the limit of detection. The parent molecule also showed potent in vitro activity against high-threat Gram-positive organisms, and JSF-2659 was shown in a deep tissue model of vancomycin-resistant Staphylococcus aureus (VRSA) and a model of Clostridioides difficile-induced colitis to be highly efficacious and protective. JSF-2659 is a novel preclinical drug candidate against high-threat multidrug resistant organisms with low potential to develop new resistance.

Tissue Distribution of [14C]-Lefamulin into the Urogenital Tract in Rats

Lefamulin, a semisynthetic pleuromutilin antibiotic approved in the United States, Canada, and Europe for intravenous and oral treatment of community-acquired bacterial pneumonia, is highly active in vitro against bacterial pathogens that cause sexually transmitted infections (STIs), including multidrug-resistant strains of Neisseria gonorrhoeae, Chlamydia trachomatis, and Mycoplasma genitalium. This nonclinical study used quantitative whole-body autoradiography (QWBA) and qualitative tape-transfer microautoradiography (MARG) to investigate lefamulin distribution into urogenital tract tissues down to a cellular level in male and female rats. A single intravenous dose (30 mg/kg) of [14C]-lefamulin was administered to 3 male and 3 female Sprague-Dawley rats. At 0.5, 6, and 24 h post dose, rats were euthanized and [14C]-lefamulin distribution was investigated using QWBA and MARG of sagittal planes. [14C]-lefamulin was well distributed throughout the carcasses of male and female rats, with the highest concentrations observed in male bulbourethral gland, urethra, prostate in female clitoral gland, uterus (particularly endometrium), and ovary. In these areas, concentrations were similar to or higher than those observed in the lungs. Concentrations peaked at 0.5 h post dose, remaining detectable in the urogenital tract up to 24 h post dose. [14C]-lefamulin in rats showed rapid, homogeneous distribution into urogenital tissues down to a cellular level, with high tissue:blood ratios in tissues relevant to STI treatment. These results, and the potent in vitro activity of lefamulin against multidrug-resistant bacteria known to cause STIs, will help inform further assessment of lefamulin, including potential clinical evaluation for treatment of STIs.

In vivo efficacy of acetazolamide in a mouse model of Neisseria gonorrhoeae infection

Gonococcal infections represent an urgent public health threat worldwide due to the increasing incidence of infections that has been accompanied by an increase in bacterial resistance to most antibiotics. This has resulted in a dwindling number of effective treatment options. Undoubtedly, there is a critical need to develop new, effective anti-gonococcal agents. In an effort to discover new anti-gonococcal therapeutics, we previously identified acetazolamide, a carbonic anhydrase inhibitor, as a novel inhibitor of Neisseria gonorrhoeae. Acetazolamide exhibited potent anti-gonococcal activity in vitro as it inhibited growth of strains of N. gonorrhoeae at concentrations that ranged from 0.5 to 4 μg/mL. The aim of this study was to investigate the in vivo efficacy of acetazolamide in a mouse model of N. gonorrhoeae genital tract infection. Compared to vehicle-treated mice, acetazolamide significantly reduced the gonococcal burden by 90% in the vagina of infected mice after three days of treatment. These results indicate that acetazolamide warrants further investigation as a promising treatment option to supplement the limited pipeline of anti-gonococcal therapeutics.

Preclinical Testing of Vaccines and Therapeutics for Gonorrhea in Female Mouse Models of Lower and Upper Reproductive Tract Infection

Murine models of Neisseria gonorrhoeae lower reproductive tract infection are valuable systems for studying N. gonorrhoeae adaptation to the female host and immune responses to infection. These models have also accelerated preclinical testing of candidate therapeutic and prophylactic products against gonorrhea. However, because N. gonorrhoeae infection is restricted to the murine cervicovaginal region, there is a need for an in vivo system for translational work on N. gonorrhoeae pelvic inflammatory disease (PID). Here we discuss the need for well-characterized preclinical upper reproductive tract infection models for developing candidate products against N. gonorrhoeae PID, and report a refinement of the gonorrhea mouse model that supports sustained upper reproductive tract infection. To establish this new model for vaccine testing, we also tested the licensed meningococcal 4CMenB vaccine, which cross-protects against murine N. gonorrhoeae lower reproductive tract infection, for efficacy against N. gonorrhoeae in the endometrium and oviducts following transcervical or vaginal challenge.

In vitro evaluation of antimicrobial resistance selection in Neisseria gonorrhoeae

Gonococcal infections represent an urgent public-health threat as >50% of cases caused by Neisseria gonorrhoeae strains display reduced susceptibility to at least one antimicrobial agent. We evaluated the pharmacodynamics of a number of antimicrobials against N. gonorrhoeae in order to assess the likelihood of mutant selection by these agents. The mutant prevention concentration (MPC) and mutant selection window (MSW) were determined for azithromycin, ceftriaxone, doxycycline, ertapenem, gentamicin, ciprofloxacin, levofloxacin and moxifloxacin against a wild-type strain of N. gonorrhoeae (ATCC 49226) and a gyrA mutant of ATCC 49226. Pharmacokinetic parameters, including peak concentration (C_max), half-life (t_1/2) and area under the plasma concentration-time curve over 24 h (AUC), associated with each agent were used to calculate the time within the MSW (T_MSW, percentage of the dosing interval that antimicrobial concentrations fall within the MSW), C_max/MPC ratio and AUC/MPC ratio for each antimicrobial agent. Concentrations of ceftriaxone (500 mg), ertapenem, ciprofloxacin, levofloxacin and moxifloxacin surpass the MPC for both strains. Results of pharmacodynamic analyses suggest that ertapenem, ciprofloxacin, levofloxacin and moxifloxacin may be most likely to prevent mutant selection in N. gonorrhoeae. Use of ceftriaxone, azithromycin, doxycycline or gentamicin for gonorrhoea is expected to lead to the ongoing emergence of resistance to these agents. There is a clear need to develop novel treatment regimens for gonococcal infections in order to limit the dissemination of resistance in N. gonorrhoeae.

Sexually Transmitted Infections Treatment Guidelines, 2021

These guidelines for the treatment of persons who have or are at risk for sexually transmitted infections (STIs) were updated by CDC after consultation with professionals knowledgeable in the field of STIs who met in Atlanta, Georgia, June 11–14, 2019. The information in this report updates the 2015 guidelines. These guidelines discuss 1) updated recommendations for treatment of Neisseria gonorrhoeae, Chlamydia trachomatis, and Trichomonas vaginalis; 2) addition of metronidazole to the recommended treatment regimen for pelvic inflammatory disease; 3) alternative treatment options for bacterial vaginosis; 4) management of Mycoplasma genitalium; 5) human papillomavirus vaccine recommendations and counseling messages; 6) expanded risk factors for syphilis testing among pregnant women; 7) one-time testing for hepatitis C infection; 8) evaluation of men who have sex with men after sexual assault; and 9) two-step testing for serologic diagnosis of genital herpes simplex virus. Physicians and other health care providers can use these guidelines to assist in prevention and treatment of STIs.

trans-Translation inhibitors bind to a novel site on the ribosome and clear Neisseria gonorrhoeae in vivo

Bacterial ribosome rescue pathways that remove ribosomes stalled on mRNAs during translation have been proposed as novel antibiotic targets because they are essential in bacteria and are not conserved in humans. We previously reported the discovery of a family of acylaminooxadiazoles that selectively inhibit trans-translation, the main ribosome rescue pathway in bacteria. Here, we report optimization of the pharmacokinetic and antibiotic properties of the acylaminooxadiazoles, producing MBX-4132, which clears multiple-drug resistant Neisseria gonorrhoeae infection in mice after a single oral dose. Single particle cryogenic-EM studies of non-stop ribosomes show that acylaminooxadiazoles bind to a unique site near the peptidyl-transfer center and significantly alter the conformation of ribosomal protein bL27, suggesting a novel mechanism for specific inhibition of trans-translation by these molecules. These results show that trans-translation is a viable therapeutic target and reveal a new conformation within the bacterial ribosome that may be critical for ribosome rescue pathways.

Molecular Features of Cephalosporins Important for Activity against Antimicrobial-Resistant Neisseria gonorrhoeae

The increasing prevalence of Neisseria gonorrhoeae strains exhibiting decreased susceptibility to extended-spectrum cephalosporins (ESCs) presents a challenge for the successful treatment of gonorrhea infections. To address this challenge, we evaluated a panel of 23 cephalosporins against penicillin-binding protein 2 (PBP2) from the ESC-resistant (ESC^R) N. gonorrhoeae strain H041 to determine which molecular features are important for antimicrobial activity. Structure-activity relationships (SARs) developed from acylation rate constants against PBP2 and antimicrobial susceptibilities against the H041 strain of N. gonorrhoeae, and interpreted against docking models, reveal that cephalosporins possessing large, lipophilic R₁ side chains and electronegative R₂ side chains with planar groups are associated with higher acylation rates against PBP2, but also that these same amphipathic features can lower antimicrobial activity. Based on these studies, we tested cefoperazone, one of the most effective ESCs for targeting PBP2, in the female mouse model infected with H041 and showed that it was equally or more effective than ceftriaxone or gentamicin for clearing infections. Taken together, our results reveal that two U.S. Food and Drug Administration (FDA)-approved agents (cefoperazone, ceftaroline) and one FDA-qualified infectious disease product (ceftobiprole) have potential as first-line treatments for gonorrhea and provide a framework for the future design of cephalosporins with improved activity against ESC-resistant N. gonorrhoeae.

Development of New Antimicrobials for Urogenital Gonorrhea Therapy: Clinical Trial Design Considerations

Gonorrhea remains a major public health challenge, and current recommendations for gonorrhea treatment are threatened by evolving antimicrobial resistance and a diminished pipeline for new antibiotics. Evaluations of potential new treatments for gonorrhea currently make limited use of new understanding of the pharmacokinetic and pharmacodynamic contributors to effective therapy, the prevention of antimicrobial resistance, and newer designs for clinical trials. They are hampered by the requirement to utilize combination ceftriaxone/azithromycin therapy as the comparator regimen in noninferiority trials designed to seek an indication for gonorrhea therapy. Evolving gonococcal epidemiology and clinical trial design constraints hinder the enrollment of those populations at the greatest risk for gonorrhea (adolescents, women, and persons infected with antibiotic-resistant Neisseria gonorrhoeae). This article summarizes a recent meeting on the evaluation process for antimicrobials for urogenital gonorrhea treatment and encourages the consideration of new designs for the evaluation of gonorrhea therapy.

Pharmacokinetic/pharmacodynamic considerations for new and current therapeutic drugs for uncomplicated gonorrhoea-challenges and opportunities

BACKGROUND

Increasing multidrug resistance rates in Neisseria gonorrhoeae have raised concerns and an urgent call for new antibiotics for treatment of gonorrhoea. Several decades of subdued drug development in this field and the recent failures of two new antibiotics to show non-inferiority compared with the current first-line antibiotics ceftriaxone plus azithromycin highlight the need for improved preclinical tools to predict clinical outcome of new drugs in the development process.

OBJECTIVES

To summarize current pharmacokinetic/pharmacodynamic (PK/PD) knowledge and dose-finding strategies for antibiotics against gonorrhoea.

SOURCES

Literature review of published papers and discussions by global experts at a special workshop on this topic.

CONTENT

We review current knowledge of gonococcal specific PK/PD principles and provide an update on new in vitro and in vivo models to correlate drug exposure with clinical outcome, and identify challenges and gaps in gonococcal therapeutic research.

IMPLICATIONS

Identifying the ideal antimicrobial agent and dose for treating uncomplicated urogenital and pharyngeal gonococcal disease requires appropriate validated non-clinical PK/PD models. Recent advances in adapting in vitro and in vivo models for use in gonorrhoea are an important step for enabling the development of new drugs with reduced risk of failure in Phase 3 clinical development and diminish the risk of emergence of resistance.

Zoliflodacin: An Oral Spiropyrimidinetrione Antibiotic for the Treatment of Neisseria gonorrheae, Including Multi-Drug-Resistant Isolates

The Centers for Disease Control and the World Health Organization have issued a list of priority pathogens for which there are dwindling therapeutic options, including antibiotic-resistant Neisseria gonorrheae, for which novel oral agents are urgently needed. Zoliflodacin, the first in a new class of antibacterial agents called the spiropyrimidinetriones, is being developed for the treatment of gonorrhea. It has a unique mode of inhibition against bacterial type II topoisomerases with binding sites in bacterial gyrase that are distinct from those of the fluoroquinolones. Zoliflodacin is bactericidal, with a low frequency of resistance and potent antibacterial activity against N. gonorrheae, including multi-drug-resistant strains (MICs ranging from ≤0.002 to 0.25 μg/mL). Although being developed for the treatment of gonorrhea, zoliflodacin also has activity against Gram-positive, fastidious Gram-negative, and atypical pathogens. A hollow-fiber infection model using S. aureus showed that that pharmacokinetic/pharmacodynamic index of fAUC/MIC best correlated with efficacy in in vivo neutropenic thigh models in mice. This data and unbound exposure magnitudes derived from the thigh models were subsequently utilized in a surrogate pathogen approach to establish dose ranges for clinical development with N. gonorrheae. In preclinical studies, a wide safety margin supported progression to phase 1 studies in healthy volunteers, which showed linear pharmacokinetics, good oral bioavailability, and no significant safety findings. In a phase 2 study, zoliflodacin was effective in treating gonococcal urogenital and rectal infections. In partnership with the Global Antibiotic Research Development Program (GARDP), zoliflodacin is currently being studied in a global phase 3 clinical trial. Zoliflodacin represents a promising new oral therapy for drug-resistant infections caused by N. gonorrheae.

Generality of Post-Antimicrobial Treatment Persistence of Borrelia burgdorferi Strains N40 and B31 in Genetically Susceptible and Resistant Mouse Strains

A basic feature of infection caused by Borrelia burgdorferi, the etiological agent of Lyme borreliosis, is that persistent infection is the rule in its many hosts. The ability to persist and evade host immune clearance poses a challenge to effective antimicrobial treatment. A link between therapy failure and the presence of persister cells has started to emerge. There is growing experimental evidence that viable but noncultivable spirochetes persist following treatment with several different antimicrobial agents. The current study utilized the mouse model to evaluate if persistence occurs following antimicrobial treatment in disease-susceptible (C3H/HeJ [C3H]) and disease-resistant (C57BL/6 [B6]) mouse strains infected with B. burgdorferi strains N40 and B31 and to confirm the generality of this phenomenon, as well as to assess the persisters' clinical relevance. The status of infection was evaluated at 12 and 18 months after treatment. The results demonstrated that persistent spirochetes remain viable for up to 18 months following treatment, as well as being noncultivable. The phenomenon of persistence in disease-susceptible C3H mice is equally evident in disease-resistant B6 mice and not unique to any particular B. burgdorferi strain. The results also demonstrate that, following antimicrobial treatment, both strains of B. burgdorferi, N40 and B31, lose one or more plasmids. The study demonstrated that noncultivable spirochetes can persist in a host following antimicrobial treatment for a long time but did not demonstrate their clinical relevance in a mouse model of chronic infection. The clinical relevance of persistent spirochetes beyond 18 months following antimicrobial treatment requires further studies in other animal models.

World Health Organization Global Gonococcal Antimicrobial Surveillance Program (WHO GASP): review of new data and evidence to inform international collaborative actions and research efforts

Antimicrobial resistance (AMR) in Neisseria gonorrhoeae is a serious public health problem, compromising the management and control of gonorrhoea globally. Resistance in N. gonorrhoeae to ceftriaxone, the last option for first-line empirical monotherapy of gonorrhoea, has been reported from many countries globally, and sporadic failures to cure especially pharyngeal gonorrhoea with ceftriaxone monotherapy and dual antimicrobial therapies (ceftriaxone plus azithromycin or doxycycline) have been confirmed in several countries. In 2018, the first gonococcal isolates with ceftriaxone resistance plus high-level azithromycin resistance were identified in England and Australia. The World Health Organization (WHO) Global Gonococcal Antimicrobial Surveillance Program (GASP) is essential to monitor AMR trends, identify emerging AMR and provide evidence for refinements of treatment guidelines and public health policy globally. Herein we describe the WHO GASP data from 67 countries in 2015-16, confirmed gonorrhoea treatment failures with ceftriaxone with or without azithromycin or doxycycline, and international collaborative actions and research efforts essential for the effective management and control of gonorrhoea. In most countries, resistance to ciprofloxacin is exceedingly high, azithromycin resistance is present and decreased susceptibility or resistance to ceftriaxone has emerged. Enhanced global collaborative actions are crucial for the control of gonorrhoea, including improved prevention, early diagnosis, treatment of index patient and partner (including test-of-cure), improved and expanded AMR surveillance (including surveillance of antimicrobial use and treatment failures), increased knowledge of correct antimicrobial use and the pharmacokinetics and pharmacodynamics of antimicrobials and effective drug regulations and prescription policies (including antimicrobial stewardship). Ultimately, rapid, accurate and affordable point-of-care diagnostic tests (ideally also predicting AMR and/or susceptibility), new therapeutic antimicrobials and, the only sustainable solution, gonococcal vaccine(s) are imperative.

Could Dampening Expression of the Neisseria gonorrhoeae mtrCDE-Encoded Efflux Pump Be a Strategy To Preserve Currently or Resurrect Formerly Used Antibiotics To Treat Gonorrhea?

Neisseria gonorrhoeae has developed resistance to every antibiotic introduced for treatment of gonorrhea since 1938, and concern now exists that gonorrheal infections may become refractory to all available antibiotics approved for therapy. The current recommended dual antibiotic treatment regimen of ceftriaxone (CRO) and azithromycin (AZM) is threatened with the emergence of gonococcal strains displaying resistance to one or both of these antibiotics. Non-beta-lactamase resistance to penicillin and third-generation cephalosporins, as well as low-level AZM resistance expressed by gonococci, requires overexpression of the mtrCDE-encoded efflux pump, which in wild-type (WT) strains is subject to transcriptional repression by MtrR. Since earlier studies showed that loss of MtrCDE renders gonococci hypersusceptible to beta-lactams and macrolides, we hypothesized that transcriptional dampening of mtrCDE would render an otherwise resistant strain susceptible to these antibiotics as assessed by antibiotic susceptibility testing and during experimental infection. In order to test this hypothesis, we ectopically expressed a WT copy of the mtrR gene, which encodes the repressor of the mtrCDE efflux pump operon, in N. gonorrhoeae strain H041, the first reported gonococcal strain to cause a third-generation-cephalosporin-resistant infection. We now report that MtrR production can repress the expression of mtrCDE, increase antimicrobial susceptibility in vitro, and enhance beta-lactam efficacy in eliminating gonococci as assessed in a female mouse model of lower genital tract infection. We propose that strategies that target the MtrCDE efflux pump should be considered to counteract the increasing problem of antibiotic-resistant gonococci.IMPORTANCE The emergence of gonococcal strains resistant to past or currently used antibiotics is a global public health concern, given the estimated 78 million infections that occur annually. The dearth of new antibiotics to treat gonorrhea demands that alternative curative strategies be considered to counteract antibiotic resistance expressed by gonococci. Herein, we show that decreased expression of a drug efflux pump that participates in gonococcal resistance to antibiotics can increase gonococcal susceptibility to beta-lactams and macrolides under laboratory conditions, as well as improve antibiotic-mediated clearance of gonococci from the genital tract of experimentally infected female mice.