Experimental Infection of Pig-Tailed Macaques (Macaca nemestrina) with Mycoplasma genitalium

Detection of human IgG antibodies against Mycoplasma genitalium using a recombinant MG075 antigen

Mycoplasma genitalium is a sexually transmitted pathogen that can cause a range of reproductive tract diseases in both men and women. To disentangle the relationship between M. genitalium infection(s) and subsequent reproductive health complications at the population level, accurate serological tools are needed. The major challenge in developing specific M. genitalium serological tests is the extensive cross-reactivity with the closely related ubiquitous respiratory tract pathogen, Mycoplasma pneumoniae. In this report, we describe the development of an immunoblot assay based on a recombinant fragment of the M. genitalium MG075 protein present in lipid-associated membrane extracts. A sensitivity of 87.1% was achieved based on the testing antibody responses in sera from 101 adults with PCR-confirmed M. genitalium infection. A specificity of 95.2% was obtained through the evaluation of sera from 166 children under 15 years of age with and without M. pneumoniae infection, who were unlikely to have been exposed to sexually transmitted M. genitalium. The development of a serological assay capable of accurately distinguishing M. genitalium and M. pneumoniae will enable a better understanding of associations between M. genitalium and adverse reproductive sequelae.

IMPORTANCE

Mycoplasma genitalium is the second most common sexually transmitted bacterial infection after chlamydia. The long-term consequences of the infection are still under investigation, but reliable tools for monitoring exposure by detection of antibodies have been lacking specificity due to the presence of cross-reacting antibodies to the closely related Mycoplasma pneumoniae. Here, we describe a novel diagnostic antigen with promising sensitivity (87%) and specificity (95%) based on testing of sera from patients with PCR-confirmed M. genitalium infection and children with and without M. pneumoniae infection, respectively. The MG075F1 antigen was expressed in Escherichia coli, and the recombinant antigen was used in a western line-blot. Due to the insolubility of the antigen, harsh denaturing conditions were needed, making an enzyme-linked immunosorbent assay (ELISA) format impossible. Future work should explore shorter fragments or protein engineering to allow for assay designs better suited for high-throughput screening.

The fungal natural product fusidic acid demonstrates potent activity against Mycoplasma genitalium

Antimicrobial resistance is extremely common in Mycoplasma genitalium, a frequent cause of urethritis in men and cervicitis, vaginitis, and pelvic inflammatory disease in women. Treatment of M. genitalium infections is difficult due to intrinsic and acquired resistance to many antibiotic classes. We undertook a program to identify novel antimicrobials with activity against M. genitalium from fungal natural products. Extracts of Ramularia coccinea contained a molecule with potent activity that was subsequently identified as fusidic acid, a fusidane-type antibiotic that has been in clinical use for decades outside the United States. We found that minimum inhibitory concentrations of fusidic acid ranged from 0.31 to 4 µg/mL among 17 M. genitalium strains including laboratory-passaged and low-passage clinical isolates. Time-kill data indicate that bactericidal killing occurs when M. genitalium is exposed to ≥10 µg/mL for 48 h, comparing favorably to serum concentrations obtained from typical loading dose regimens. Resistance to fusidic acid was associated with mutations in fusA consistent with the known mechanism of action in which fusidic acid inhibits protein synthesis by binding to elongation factor G. Interestingly, no mutants resistant to >10 µg/mL fusidic acid were obtained and a resistant strain containing a F435Y mutation in FusA was impaired for growth in vitro. These data suggest that fusidic acid may be a promising option for the treatment of M. genitalium infections.

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.

Update in Epidemiology and Management of Mycoplasma genitalium Infections

Mycoplasma genitalium is a frequent cause of urogenital syndromes in men and women and is associated with adverse sequelae in women. M genitalium also infects the rectum, and may cause proctitis, but rarely infects the pharynx. Diagnosis requires nucleic acid amplification testing. Antibiotic resistance is widespread: more than half of infections are resistant to macrolides and fluoroquinolone resistance is increasing. Resistance-guided therapy is recommended for symptomatic patients, involving initial treatment with doxycycline to reduce organism load followed by azithromycin for macrolide-sensitive infections or moxifloxacin for macrolide-resistant infections. Neither screening nor tests of cure are recommended in asymptomatic persons.

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.

Ascending Reproductive Tract Infection in Pig-Tailed Macaques Inoculated with Mycoplasma genitalium

Mycoplasma genitalium is a sexually transmitted bacterial pathogen that causes urogenital disease in men and women. M. genitalium infections can persist for months to years and can ascend to the upper reproductive tract in women where it is associated with serious sequelae including pelvic inflammatory disease, tubal factor infertility, and preterm birth. An animal model is needed to understand immune evasion strategies that allow persistence, mechanisms of ascending infection, and factors associated with clearance. In earlier studies, we determined that pig-tailed macaques are susceptible to cervical infection; however, not all primates were successfully infected, persistence varied between animals, and ascension to the upper reproductive tract was not observed after 4 or 8 weeks of follow-up. Building on our previous findings, we refined our inoculation methods to increase infection rates, extended observation to 18 weeks, and comprehensively sampled the upper reproductive tract to detect ascending infection. With these improvements, we established infection in all (3/3) primates inoculated with M. genitalium and demonstrated lower tract persistence for 16 to 18 weeks. Ascension to the upper reproductive tract at endpoint was observed in two out of three primates. All three primates developed serum and local antibodies reacting primarily to the MgpB and MgpC adherence proteins. Elevated genital polymorphonuclear leukocytes (PMNs) and inflammatory cytokines and chemokines, erythema of the ectocervix in one primate, and histologic evidence of vaginitis and endocervicitis in two primates suggest a mild to moderate inflammatory response to infection. This model will be valuable to understand the natural history of M. genitalium infection including mechanisms of persistence, immune evasion, and ascension to the upper reproductive tract.

Azithromycin and Doxycycline Resistance Profiles of U.S. Mycoplasma genitalium Strains and Their Association with Treatment Outcomes

Mycoplasma genitalium is a sexually transmitted bacterium associated with nongonococcal urethritis (NGU) in men and cervicitis, endometritis, and pelvic inflammatory disease in women. Effective treatment is challenging due to the inherent, and increasingly acquired, antibiotic resistance in this pathogen. In our treatment trial conducted from 2007 to 2011 in Seattle, WA, we demonstrated poor efficacy of azithromycin (AZM) and doxycycline (DOX) against M. genitalium among men with NGU. In the present study, we cultured M. genitalium from 74 of 80 (92.5%) PCR-positive men at enrollment (V-1) and defined the MICs of AZM (N = 56 isolates) of DOX (N = 62 isolates). Susceptibility to AZM was bimodal; MICs were >8 μg/ml (44.6%) and <0.004 μg/ml (55.4%) for these isolates. The association of MIC with treatment efficacy was determined for men initially treated with either AZM (N = 30) or DOX (N = 24). Men treated with AZM were more likely to experience microbiologic treatment failure (P < 0.001) if infected with isolates that had AZM MICs of >8 μg/ml (18/18 men) than those with isolates that had AZM MICs of <0.004 μg/ml (1/12 men). Clinical treatment failure also was more likely to occur (P = 0.002) with AZM MICs of >8 μg/ml (12/18 men) than with AZM MICs of <0.004 μg/ml (1/12 men). In contrast, DOX MICs ranged from <0.125 to 2 μg/ml and were not correlated with microbiologic (P = 0.71) or clinical treatment (P = 0.41) failure, demonstrating no relationship between DOX MICs and treatment efficacy. Given the rapid spread of AZM resistance and the emergence of quinolone resistance, the current second-line therapy, monitoring MICs and evaluating other potential treatments for M. genitalium will be critical.

Etiology and Diagnosis of Pelvic Inflammatory Disease: Looking Beyond Gonorrhea and Chlamydia

Pelvic inflammatory disease (PID) is a clinical syndrome that has been associated with a wide range of potential causal pathogens. Three broad groups of organisms have been isolated from the genital tract of people with PID: sexually transmitted organisms such as Neisseria gonorrhoeae, Chlamydia trachomatis, Mycoplasma genitalium, and Trichomonas vaginalis; bacterial vaginosis (BV)-associated species and genera such as Atopobium vaginae, Sneathia, and Megasphaera; and genera and species usually associated with the gastrointestinal or respiratory tracts such as Bacteroides, Escherichia coli, Streptococcus, or Haemophilus influenza. Although PID is often considered to be synonymous with gonorrhea or chlamydia, these pathogens are found in only one quarter to one third of people with PID, suggesting that broader screening and diagnostic and treatment strategies need to be considered to reduce the burden of PID and its associated sequelae.

Sequence variation and immunogenicity of the Mycoplasma genitalium MgpB and MgpC adherence proteins during persistent infection of men with non-gonococcal urethritis

Mycoplasma genitalium is a sexually transmitted bacterial pathogen that infects men and women. Antigenic variation of MgpB and MgpC, the immunodominant adherence proteins of M. genitalium, is thought to contribute to immune evasion and chronic infection. We investigated the evolution of mgpB and mgpC sequences in men with non-gonococcal urethritis persistently infected with M. genitalium, including two men with anti-M. genitalium antibodies at enrollment and two that developed antibodies during follow-up. Each of the four patients was persistently infected with a different strain type and each patient produced antibodies targeting MgpB and MgpC. Amino acid sequence evolution in the variable regions of MgpB and MgpC occurred in all four patients with changes observed in single and multiple variable regions over time. Using the available crystal structure of MgpC of the G37 type strain we found that predicted conformational B cell epitopes localize predominantly to the variable region of MgpC, amino acids that changed during patient infection lie in these epitopes, and variant amino acids are in close proximity to the conserved sialic acid binding pocket. These findings support the hypothesis that sequence variation functions to avoid specific antibodies thereby contributing to persistence in the genital tract.

The mechanisms underlying antigenic variation and maintenance of genomic integrity in Mycoplasma pneumoniae and Mycoplasma genitalium

Mycoplasma pneumoniae and Mycoplasma genitalium are important causative agents of infections in humans. Like all other mycoplasmas, these species possess genomes that are significantly smaller than that of other prokaryotes. Moreover, both organisms possess an exceptionally compact set of DNA recombination and repair-associated genes. These genes, however, are sufficient to generate antigenic variation by means of homologous recombination between specific repetitive genomic elements. At the same time, these mycoplasmas have likely evolved strategies to maintain the stability and integrity of their 'minimal' genomes. Previous studies have indicated that there are considerable differences between mycoplasmas and other bacteria in the composition of their DNA recombination and repair machinery. However, the complete repertoire of activities executed by the putative recombination and repair enzymes encoded by Mycoplasma species is not yet fully understood. In this paper, we review the current knowledge on the proteins that likely form part of the DNA repair and recombination pathways of two of the most clinically relevant Mycoplasma species, M. pneumoniae and M. genitalium. The characterization of these proteins will help to define the minimal enzymatic requirements for creating bacterial genetic diversity (antigenic variation) on the one hand, while maintaining genomic integrity on the other.

Structure and mechanism of the Nap adhesion complex from the human pathogen Mycoplasma genitalium

Mycoplasma genitalium is a human pathogen adhering to host target epithelial cells and causing urethritis, cervicitis and pelvic inflammatory disease. Essential for infectivity is a transmembrane adhesion complex called Nap comprising proteins P110 and P140. Here we report the crystal structure of P140 both alone and in complex with the N-terminal domain of P110. By cryo-electron microscopy (cryo-EM) and tomography (cryo-ET) we find closed and open Nap conformations, determined at 9.8 and 15 Å, respectively. Both crystal structures and the cryo-EM structure are found in a closed conformation, where the sialic acid binding site in P110 is occluded. By contrast, the cryo-ET structure shows an open conformation, where the binding site is accessible. Structural information, in combination with functional studies, suggests a mechanism for attachment and release of M. genitalium to and from the host cell receptor, in which Nap conformations alternate to sustain motility and guarantee infectivity.

Design and Validation of Transcription-Mediated-Amplification Nucleic Acid Amplification Tests for Mycoplasma genitalium

Mycoplasma genitalium is a sexually transmitted bacterium linked to adverse sexual and reproductive health outcomes in women and men. M. genitalium is difficult to culture, and in the absence of validated amplified molecular methods for diagnosis of infection, there is no reference standard available for use as a comparator for the validation of new M. genitalium diagnostic tests. We evaluated the analytical and clinical performance of three transcription-mediated amplification (TMA) tests for M. genitalium, each targeting unique rRNA sequences, for use as a composite comparator for clinical validation of the Aptima Mycoplasma genitalium (AMG) assay, an in vitro diagnostic (IVD) TMA test that targets 16 s rRNA of M. genitalium Analytical sensitivity, specificity, and strain inclusivity of all four TMA tests were determined using nine laboratory strains of M. genitalium and 56 nontarget bacteria, protozoa, and viruses. Analytical sensitivity of the tests for M. genitalium ranged from 0.017 to 0.040 genome equivalents/ml. None of the nontarget organisms evaluated cross-reacted with any test. A composite comparator reference standard consisting of the 3 alternate (Alt) TMA tests was used to evaluate the clinical performance of the AMG assay by testing residual vaginal swab, female urine, and male urine specimens obtained from 1,400 adult subjects from three U.S. clinical sites. Using this reference standard to establish infected specimen status, the sensitivity, specificity, and overall agreement of the AMG IVD assay were 100%, 99.9%, and 99.9%, respectively. These results demonstrate the utility of molecular composite reference standard methodology for the clinical validation of future IVD tests for this organism.

Mycoplasma genitalium adhesin P110 binds sialic-acid human receptors

Adhesion of pathogenic bacteria to target cells is a prerequisite for colonization and further infection. The main adhesins of the emerging sexually transmitted pathogen Mycoplasma genitalium, P140 and P110, interact to form a Nap complex anchored to the cell membrane. Herein, we present the crystal structures of the extracellular region of the virulence factor P110 (916 residues) unliganded and in complex with sialic acid oligosaccharides. P110 interacts only with the neuraminic acid moiety of the oligosaccharides and experiments with human cells demonstrate that these interactions are essential for mycoplasma cytadherence. Additionally, structural information provides a deep insight of the P110 antigenic regions undergoing programmed variation to evade the host immune response. These results enlighten the interplay of M. genitalium with human target cells, offering new strategies to control mycoplasma infections.

How the Mycoplasma genitalium cytadhesins P140 and P110 promote host cell invasion remains poorly understood. Here, combining structural analysis with functional assays, Aparicio et al. identify the P110 domain that binds to sialylated receptors essential for mycoplasma cytadherence.

Activation of σ20-dependent recombination and horizontal gene transfer in Mycoplasma genitalium

In the human pathogen Mycoplasma genitalium, homologous recombination is under the control of σ20, an alternative sigma factor that boosts the generation of genetic and antigenic diversity in the population. Under laboratory growth conditions, σ20 activation is rare and the factors governing its intermittent activity are unknown. Two σ20-regulated genes, rrlA and rrlB, showed to be important for recombination of homologous DNA sequences in this bacterium. Herein, we demonstrate that rrlA and rrlB code for two small proteins that participate in a feed-forward loop essential for σ20 function. In addition, we identify novel genes regulated by σ20 and show that several non-coding regions, which function as a reservoir for the generation of antigenic diversity, are also activated by this alternative sigma factor. Finally, we reveal that M. genitalium cells can transfer DNA horizontally by a novel mechanism that requires RecA and is facilitated by σ20 over-expression. This DNA transfer system is arguably fundamental for persistence of M. genitalium within the host since it could facilitate a rapid dissemination of successful antigenic variants within the population. Overall, these findings impose a novel conception of genome evolution, genetic variation and survival of M. genitalium within the host.

Mycoplasma genitalium Nonadherent Phase Variants Arise by Multiple Mechanisms and Escape Antibody-Dependent Growth Inhibition

Antigenic variation of the immunodominant MgpB and MgpC proteins has been suggested to be a mechanism of immune evasion of the human pathogen Mycoplasma genitalium, a cause of several reproductive tract disease syndromes. Phase variation resulting in the loss of adherence has also been documented, but the molecular mechanisms underlying this process and its role in pathogenesis are still poorly understood. In this study, we isolated and characterized 40 spontaneous, nonadherent phase variants from in vitro-passaged M. genitalium cultures. In all cases, nonadherence was associated with the loss of MgpBC protein expression, attributable to sequence changes in the mgpBC expression site. Phase variants were grouped into seven classes on the basis of the nature of the mutation. Consistent with the established role of RecA in phase variation, 31 (79.5%) variants arose via recombination with MgPa repeat regions that contain mgpBC variable sequences. The remaining mutants arose via nonsense or frameshift mutations. As expected, revertants were obtained for phase variants that were predicted to be reversible but not for those that arose via an irreversible mechanism. Furthermore, phase variants were enriched in M. genitalium cultures exposed to antibodies reacting to the extracellular, conserved C terminus of MgpB but not in cultures exposed to antibodies reacting to an intracellular domain of MgpB or the cytoplasmic HU protein. Genetic characterization of the antibody-selected phase variants confirmed that they arose via reversible and irreversible recombination and point mutations within mgpBC These phase variants resisted antibody-mediated growth inhibition, suggesting that phase variation promotes immune evasion.

Contribution of the swine model in the study of human sexually transmitted infections

The pig has garnered more and more interest as a model animal to study various conditions in humans. The growing success of the pig as an experimental animal model is explained by its similarities with humans in terms of anatomy, genetics, immunology, and physiology, by their manageable behavior and size, and by the general public acceptance of using pigs for experimental purposes. In addition, the immunological toolbox of pigs has grown substantially in the last decade. This development led to a boost in the use of pigs as a preclinical model for various human infections including sexually transmitted diseases (STIs) like Chlamydia trachomatis. In the current review, we discuss the use of animal models for biomedical research on the major human STIs. We summarize results obtained in the most common animal models and focus on the contributions of the pig model towards the understanding of pathogenesis and the host immune response. In addition, we present the main features of the porcine model that are particularly relevant for the study of pathogens affecting human female and male genital tracts. We also inform on the technological advancements in the porcine toolbox to facilitate new discoveries in this biologically important animal model. There is a continued need for improvements in animal modeling for biomedical research inclusive STI research. With all its advantages and the highly improved toolbox, the porcine model can play a crucial role in STI research and open the door to new exciting discoveries.

The Unique Microbiology and Molecular Pathogenesis of Mycoplasma genitalium

Mycoplasma genitalium is increasingly appreciated as a common cause of sexually transmitted disease syndromes, including urethritis in men and cervicitis, endometritis, pelvic inflammatory disease, and possibly preterm birth, tubal factor infertility, and ectopic pregnancy in women. Despite these disease associations, which parallel those of Chlamydia trachomatis and Neisseria gonorrhoeae, the mechanisms by which this pathogen elicits inflammation, causes cellular damage, and persists in its only natural host (humans) are unique and are not fully understood. The purpose of this review is to briefly provide a historical background on the discovery, microbiology, and recognition of M. genitalium as a pathogen, and then summarize the recent advances in our understanding of the molecular biology and pathogenesis of this unique urogenital organism. Collectively, the basic scientific discussions herein should provide a framework for understanding the clinical and epidemiological outcomes described in the accompanying articles in this supplemental issue.

Mycoplasma genitalium in Women: Current Knowledge and Research Priorities for This Recently Emerged Pathogen

Health consequences of sexually transmitted diseases disproportionately affect women, making it important to determine whether newly emerged pathogens cause sequelae. Although the pathogenic role of Mycoplasma genitalium in male urethritis is clear, fewer studies have been conducted among women to determine its pathogenic role in the female reproductive tract. Pelvic inflammatory disease (PID) is an important cause of infertility and ectopic pregnancy, and Chlamydia trachomatis and Neisseria gonorrhoeae are recognized microbial causes. Emerging data demonstrate an association between M. genitalium and PID, and limited data suggest associations with infertility and preterm birth, yet the attributable risk for female genital tract infections remains to be defined. Further investigations are needed to better define the impact of M. genitalium on women's reproductive health. Importantly, prospective studies evaluating whether screening programs and targeted treatment of M. genitalium improve reproductive outcomes in women are necessary to guide public health policy for this emerging pathogen.