Inhibition of bacterial FMN transferase: A potential avenue for countering antimicrobial resistance.

Antibiotic resistance is a challenge for the control of bacterial infections. In an effort to explore unconventional avenues for antibacterial drug development, we focused on the FMN-transferase activity of the enzyme Ftp from the syphilis spirochete, Treponema pallidum (Ftp_Tp). This enzyme, which is only found in prokaryotes and trypanosomatids, post-translationally modifies proteins in the periplasm, covalently linking FMN (from FAD) to proteins that typically are important for establishing an essential electrochemical gradient across the cytoplasmic membrane. As such, Ftp inhibitors potentially represent a new class of antimicrobials. Previously, we showed that AMP is both a product of the Ftp_tp-catalyzed reaction and an inhibitor of the enzyme. As a preliminary step in exploiting this property to develop a novel Ftp_Tp inhibitor, we have used structural and solution studies to examine the inhibitory and enzyme-binding properties of several adenine-based nucleosides, with particular focus on the 2-position of the purine ring. Implications for future drug design are discussed.

Efficacy of linezolid on Treponema pallidum, the syphilis agent: A preclinical study.

BACKGROUND: Penicillin G, the current standard treatment for syphilis, has important drawbacks, but virtually no preclinical or clinical studies have been performed to identify viable alternatives. We tested, both in vitro and in vivo, three marketed antibiotics with adequate pharmacological properties to treat syphilis. METHODS: We used an in vitro culturing system of T. pallidum to perform drug susceptibility testing and applied quantitative PCR targeting the tp0574 gene to measure bacterial growth. To confirm in vivo efficacy, fifteen rabbits were infected intradermally with T. pallidum at eight sites each and randomly allocated to an experimental treatment (linezolid, moxifloxacin, clofazimine) or a control arm (benzathine penicillin G [BPG], untreated). The primary outcome was treatment efficacy defined as the time to lesion healing measured from the date of treatment start. Secondary outcomes were absence of treponemes or treponemal mRNA in injection sites, absence of seroconversion, and cerebrospinal fluid (CSF) abnormalities and negative rabbit infectivity tests (RIT). FINDINGS: Linezolid showed in vitro bactericidal activity at concentrations of 0.5 µg/mL or higher. When administered orally to experimentally infected rabbits, it induced healing of early lesions at a time similar to BPG (hazard ratio 3.84; 95% CI 2.05-7.17; p < 0.0001 compared to untreated controls). In linezolid-treated animals, dark-field microscopy and qPCR assessment showed no presence of treponemes after day 3 post-treatment start, serologic test did not convert to positive, CSF had no abnormalities, and RIT was negative. Moxifloxacin and clofazimine failed to inhibit bacterial growth in vitro and could not cure the infection in the rabbit model. INTERPRETATION: Linezolid, a low-cost oxazolidinone, has in vitro and in vivo activity against T. pallidum, with efficacy similar to BPG in treating treponemal lesions in the animal model. Our findings warrant further research to assess the efficacy of linezolid as an alternative to penicillin G to treat syphilis in human clinical trials. FUNDING: European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program (Grant agreement No. 850450).

Phase II trial evaluating the clinical efficacy of cefixime for treatment of active syphilis in non-pregnant women in Brazil (CeBra).

BACKGROUND: Syphilis is a sexually and vertically transmitted infection caused by the bacteria Treponema pallidum for which there are few proven alternatives to penicillin for treatment. For pregnant women infected with syphilis, penicillin is the only WHO-recommended treatment that will treat the mother and cross the placenta to treat the unborn infant and prevent congenital syphilis. Recent shortages, national level stockouts as well as other barriers to penicillin use call for the urgent identification of alternative therapies to treat pregnant women infected with syphilis. METHODS: This prospective, randomized, non-comparative trial will enroll non-pregnant women aged 18 years and older with active syphilis, defined as a positive rapid treponemal and a positive non-treponemal RPR test with titer ≥1:16. Women will be a, domized in a 2:1 ratio to receive the oral third generation cephalosporin cefixime at a dose of 400 mg two times per day for 10 days (n = 140) or benzathine penicillin G 2.4 million units intramuscularly based on the stage of syphilis infection (n = 70). RPR titers will be collected at enrolment, and at three, six, and nine months following treatment. Participants experiencing a 4-fold (2 titer) decline by 6 months will be considered as having an adequate or curative treatment response. DISCUSSION: Demonstration of efficacy of cefixime in the treatment of active syphilis in this Phase 2 trial among non-pregnant women will inform a proposed randomized controlled trial to evaluate cefixime as an alternative treatment for pregnant women with active syphilis to evaluate prevention of congenital syphilis. TRIAL REGISTRATION: Trial identifier: www.Clinicaltrials.gov, NCT03752112. Registration Date: November 22, 2018.

Treponema pallidum putative novel drug target identification and validation: rethinking syphilis therapeutics with plant-derived terpenoids.

Syphilis, a slow progressive and the third most common sexually transmitted disease found worldwide, is caused by a spirochete gram negative bacteria Treponema pallidum. Emergence of antibiotic resistant T. pallidum has led to a search for novel drugs and their targets. Subtractive genomics analyses of pathogen T. pallidum and host Homo sapiens resulted in identification of 126 proteins essential for survival and viability of the pathogen. Metabolic pathway analyses of these essential proteins led to discovery of nineteen proteins distributed among six metabolic pathways unique to T. pallidum. One hundred plant-derived terpenoids, as potential therapeutic molecules against T. pallidum, were screened for their drug likeness and ADMET (absorption, distribution, metabolism, and toxicity) properties. Subsequently the resulting nine terpenoids were docked with five unique T. pallidum targets through molecular modeling approaches. Out of five targets analyzed, D-alanine:D-alanine ligase was found to be the most promising target, while terpenoid salvicine was the most potent inhibitor. A comparison of the inhibitory potential of the best docked readily available natural compound, namely pomiferin (flavonoid) with that of the best docked terpenoid salvicine, revealed that salvicine was a more potent inhibitor than that of pomiferin. To the best of our knowledge, this is the first report of a terpenoid as a potential therapeutic molecule against T. pallidum with D-alanine:D-alanine ligase as a novel target. Further studies are warranted to evaluate and explore the potential clinical ramifications of these findings in relation to syphilis that has public health importance worldwide.

Jarisch-Herxheimer reaction among HIV-positive patients with early syphilis: azithromycin versus benzathine penicillin G therapy.

INTRODUCTION: The Jarisch-Herxheimer reaction, a febrile inflammatory reaction that often occurs after the first dose of chemotherapy in spirochetal diseases, may result in deleterious effects to patients with neurosyphilis and to pregnant women. A single 2-g oral dose of azithromycin is an alternative treatment to benzathine penicillin G for early syphilis in areas with low macrolide resistance. With its potential anti-inflammatory activity, the impact of azithromycin on the incidence of the Jarisch-Herxheimer reaction in HIV-positive patients with early syphilis has rarely been investigated. METHODS: In HIV-positive patients with early syphilis, the Jarisch-Herxheimer reaction was prospectively investigated using the same data collection form in 119 patients who received benzathine penicillin G between 2007 and 2009 and 198 who received azithromycin between 2012 and 2013, when shortage of benzathine penicillin G occurred in Taiwan. Between 2012 and 2013, polymerase chain reaction (PCR) assay was performed to detect Treponema pallidum DNA in clinical specimens, and PCR restriction fragment length polymorphism of the 23S ribosomal RNA was performed to detect point mutations (2058G or A2059G) that are associated with macrolide resistance. RESULTS: The overall incidence of the Jarisch-Herxheimer reaction was significantly lower in patients receiving azithromycin than those receiving benzathine penicillin G (14.1% vs. 56.3%, p<0.001). The risk increased with higher rapid plasma reagin (RPR) titres (adjusted odds ratio [AOR] per 1-log2 increase, 1.21; confidence interval [CI], 1.04-1.41), but decreased with prior penicillin therapy for syphilis (AOR, 0.37; 95% CI, 0.19-0.71) and azithromycin treatment (AOR, 0.15; 95% CI, 0.08-0.29). During the study period, 310 specimens were obtained from 198 patients with syphilis for PCR assays, from whom T. pallidum was identified in 76 patients, one of whom (1.3%) was found to be infected with T. pallidum harbouring the macrolide resistance mutation (A2058G). In subgroup analyses confined to the 75 patients infected with T. pallidum lacking resistance mutation, a statistically significantly lower risk for the Jarisch-Herxheimer reaction following azithromycin treatment was noted. CONCLUSIONS: Treatment with azithromycin was associated with a lower risk for the Jarisch-Herxheimer reaction than that with benzathine penicillin G in HIV-positive patients with early syphilis. Previous benzathine penicillin G therapy for syphilis decreased the risk, whereas higher RPR titres increased the risk, for the reaction.

[The cytoarchitectonics of hard chancre in rabbits with experimental syphilis exposed to soliusul'fon and cefamezine]. / Tsitoarkhitektonika tverdogo shankra u krolikov s éksperimental'nym sifilisom pri vozdeistvii soliusul'fonom i tsefamezinom.

Twenty rabbits were infected with Treponema pallidum suspension. Ten animals were injected with solusulfone, the rest with cefamezin. Specific features of syphilis induced by a pool of Treponemas are described, such as T. pallidum ultrastructure, formation of a specific granule, form of the agent aggression. Solusulfone treatment was associated with activation of phagocytosis, that manifested by a shift of the incomplete/complete phagocytosis ratio towards the reaction completion; however, intact T. pallidum were detectable even in 72 hrs after the drug injection. Cefamezin had no effect on the cysts and cyst-like formations at the beginning of the treatment course but these forms of the agent were already undetectable in 48 hours.

Interaction of Treponema pallidum (Nichols strain) with cultured mammalian cells: effects of oxygen, reducing agents, serum supplements, and different cell types.

Cultured mammalian cells extend the time of survival of Treponema pallidum (Nichols strain). Various parameters that have been previously shown to enhance treponemal survival in vitro were examined for influences on the interaction of T. pallidum with cultured cells. With cells derived from normal rabbit testes, the time of retention of treponemal virulence was extended in an atmosphere containing reduced concentrations of oxygen. Glutathione and cysteine, when added to the basal tissue culture medium, prolonged treponemal survival. In an assessment of various tissue culture medium supplements, normal rabbit serum was equivalent to fetal bovine serum and superior to bovine serum albumin fraction V (BSA), fatty acid-poor BSA, and lipid-pooed for TRK-2, HSE, NRK, and C6 cells. Dithiotreitol, as an additional reducing agent, sharply enhanced treponemal survival. With SF1Ep NBL-11 cells and basal tissue culture medium containing glutathione, cysteine, and dithiothreitol, in an atmosphere of approximately 3% oxygen, T. pallidum was maintained without detectable decreases in the number of virulent organisms for 6 days.

Treponema pallidum in early syphilitic lesions in humans during high-dosage penicillin therapy. An electron microscopical study.

The alterations of early syphilitic infection occuring in the course of high dosage penicillin (120 mega IU, 36 h) as clinical experimental trial has been studied both from the clinical and the electron microscopical views. By electron microscopical studies, findings revealing the localization and the status of treponemes before and during penicillin treatment could be established. Before treatment started, the majority of treponemes was of intercellular localization. In the course of treatment various forms of destruction could be differentiated. The most striking change in the host tissue after 7-8 h of penicillin therapy was an elimination of treponemes by penetrating phagocytes. 24 h after the beginning of treatment, treponemes could not be demonstrated any more. The clinical and serological findings after the high dosage penicilline will produce results comparable to those of conventional therapie.

Investigations on in vitro survival and virulence of T. pallidum under aerobiosis.

Motility of pathogenic T. pallidum was maintained in aerobic in vitro cultures for several weeks using a special medium. The latter consisted of McCoy's 5a medium supplemented with glutathione, sodium pyruvate, HEPES buffer, gentamycin (garamycin), and fetal calf serum. The virulence of the organisms was lost in 5 to 6 days. No multiplication of the organisms was observed. Four antibiotics (viomycin, kanamycin, gentamycin (garamycin), and neomycin) were tested for their bactericidal action and possible toxicity to T. pallidum. Gentamycin proved to be superior to the other three antibiotics in being non-toxic to the treponemes and showing a possible stimulatory effect on their motility and longevity. Cultivation of T. pallidum in cultured cells in the presence of the enzymes, superoxide dismutase and catalase, in a special medium showed possibilities for future experimentation under monitored, reduced oxygen pressure with a continuous system to dismutate superoxide radicals.