Iron(III) Binding Properties of PF1140, a Fungal N-Hydroxypyridone, and Activity against Mycoplasma genitalium.

Mycoplasma genitalium is a sexually transmitted bacterium associated with urogenital disease syndromes in the US and worldwide. The global rise in drug resistance in M. genitalium necessitates the development of novel drugs to treat this pathogen. To address this need, we have screened extracts from a library of fungal isolates assembled through the University of Oklahoma Citizen Science Soil Collection Program. Analysis of one of the bioactive extracts using bioassay-guided fractionation led to the purification of the compound PF1140 (1) along with a new and several other known pyridones. The N-hydroxy pyridones are generally regarded as siderophores with high binding affinity for iron(III) under physiological conditions. Results from UV-vis absorption spectroscopy-based titration experiments revealed that 1 complexes with Fe3+. As M. genitalium does not utilize iron, we propose that the PF1140-iron complex induces cytotoxicity by facilitating the cellular uptake of iron, which reacts with endogenous hydrogen peroxide to produce toxic hydroxyl radicals.

Serum and Urethral Antibody Response in Mycoplasma genitalium -Infected Men.

ABSTRACT: The antibody response to Mycoplasma genitalium in serum and urethral secretions of men with nongonococcal urethritis was examined longitudinally. Serum and urethral antibodies reacted primarily with the MgpB and MgpC adhesins. Serum antibodies persisted throughout follow-up, whereas urethral antibodies waned despite organism persistence. Declining antibodies may facilitate chronic infection.

Appraisal of Fungus-Derived Xanthoquinodins as Broad-Spectrum Anti-Infectives Targeting Phylogenetically Diverse Human Pathogens.

Xanthoquinodins make up a distinctive class of xanthone-anthraquinone heterodimers reported as secondary metabolites from several fungal species. Through a collaborative multi-institutional screening program, a fungal extract prepared from a Trichocladium sp. was identified that exhibited strong inhibitory effects against several human pathogens (Mycoplasma genitalium, Plasmodium falciparum, Cryptosporidium parvum, and Trichomonas vaginalis). This report focuses on one of the unique samples that exhibited a desirable combination of biological effects: namely, it inhibited all four test pathogens and demonstrated low levels of toxicity toward HepG2 (human liver) cells. Fractionation and purification of the bioactive components and their congeners led to the identification of six new compounds [xanthoquinodins NPDG A1-A5 (1-5) and B1 (6)] as well as several previously reported natural products (7-14). The chemical structures of 1-14 were determined based on interpretation of their 1D and 2D NMR, HRESIMS, and electronic circular dichroism (ECD) data. Biological testing of the purified metabolites revealed that they possessed widely varying levels of inhibitory activity against a panel of human pathogens. Xanthoquinodins A1 (7) and A2 (8) exhibited the most promising broad-spectrum inhibitory effects against M. genitalium (EC50 values: 0.13 and 0.12 µM, respectively), C. parvum (EC50 values: 5.2 and 3.5 µM, respectively), T. vaginalis (EC50 values: 3.9 and 6.8 µM, respectively), and P. falciparum (EC50 values: 0.29 and 0.50 µM, respectively) with no cytotoxicity detected at the highest concentration tested (HepG2 EC50 > 25 µM).

In Vitro Susceptibility and Resistance of Mycoplasma genitalium to Nitroimidazoles.

Mycoplasma genitalium is a sexually transmitted reproductive tract pathogen of men and women. M. genitalium infections are increasingly difficult to treat due to poor efficacy of doxycycline and acquired resistance to azithromycin and moxifloxacin. A recent clinical trial suggested that metronidazole may improve cure rates for women with pelvic inflammatory disease and reduced the detection of M. genitalium when included with standard doxycycline plus ceftriaxone treatment. As data regarding susceptibility of mycoplasmas to nitroimidazoles are lacking in the scientific literature, we determined the in vitro susceptibility of 10 M. genitalium strains to metronidazole, secnidazole, and tinidazole. MICs ranged from 1.6 to 12.5 µg/mL for metronidazole, 3.1 to 12.5 µg/mL for secnidazole, and 0.8 to 6.3 µg/mL for tinidazole. None of these agents was synergistic with doxycycline in checkerboard broth microdilution assays. Tinidazole was superior to metronidazole and secnidazole in terms of MIC and time-kill kinetics and was bactericidal (>99.9% killing) at concentrations below reported serum concentrations. Mutations associated with nitroimidazole resistance were identified by whole-genome sequencing of spontaneous resistant mutants, suggesting a mechanism for reductive activation of the nitroimidazole prodrug by a predicted NAD(P)H-dependent flavin mononucleotide (FMN) oxidoreductase. The presence of oxygen did not affect MICs of wild-type M. genitalium, but a nitroimidazole-resistant mutant was defective for growth under anaerobic conditions, suggesting that resistant mutants may have a fitness disadvantage in anaerobic genital sites. Clinical studies are needed to determine if nitroimidazoles, especially tinidazole, are effective for eradicating M. genitalium infections in men and women.