Analysis of the Mycoplasma genitalium MgpB Adhesin to Predict Membrane Topology, Investigate Antibody Accessibility, Characterize Amino Acid Diversity, and Identify Functional and Immunogenic Epitopes

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.

Pathogenicity and virulence of Mycoplasma genitalium: Unraveling Ariadne's Thread

Mycoplasma genitalium, a pathogen from class Mollicutes, has been linked to sexually transmitted diseases and sparked widespread concern. To adapt to its environment, M. genitalium has evolved specific adhesins and motility mechanisms that allow it to adhere to and invade various eukaryotic cells, thereby causing severe damage to the cells. Even though traditional exotoxins have not been identified, secreted nucleases or membrane lipoproteins have been shown to cause cell death and inflammatory injury in M. genitalium infection. However, as both innate and adaptive immune responses are important for controlling infection, the immune responses that develop upon infection do not necessarily eliminate the organism completely. Antigenic variation, detoxifying enzymes, immunoglobulins, neutrophil extracellular trap-degrading enzymes, cell invasion, and biofilm formation are important factors that help the pathogen overcome the host defence and cause chronic infections in susceptible individuals. Furthermore, M. genitalium can increase the susceptibility to several sexually transmitted pathogens, which significantly complicates the persistence and chronicity of M. genitalium infection. This review aimed to discuss the virulence factors of M. genitalium to shed light on its complex pathogenicity and pathogenesis of the infection.

Molecular Tools for Typing Mycoplasma pneumoniae and Mycoplasma genitalium

Mycoplasma pneumoniae and Mycoplasma genitalium are cell wall-less bacteria with strongly reduced genome content and close phylogenetic relatedness. In humans, the only known natural host, the microorganisms colonize the respiratory or genitourinary mucosa and may cause a broad range of clinical presentations. Besides fundamental differences in their tissue specificity, transmission route, and ability to cause prevalence peaks, both species share similarities such as the occurrence of asymptomatic carriers, preferred populations for infection, and problems with high rates of antimicrobial resistance. To further understand the epidemiology of these practically challenging bacteria, typing of strains is necessary. Since the cultivation of both pathogens is difficult and not performed outside of specialized laboratories, molecular typing methods with adequate discriminatory power, stability, and reproducibility have been developed. These include the characterization of genes containing repetitive sequences, of variable genome regions without the presence of repetitive sequences, determination of single and multi-locus variable-number tandem repeats, and detection of single nucleotide polymorphisms in different genes, respectively. The current repertoire of procedures allows reliable differentiation of strains circulating in different populations and in different time periods as well as comparison of strains occurring subsequently in individual patients. In this review, the methods for typing M. pneumoniae and M. genitalium, including the results of their application in different studies, are summarized and current knowledge regarding the association of typing data with the clinical characteristics of infections is presented.

Mycoplasmas as Host Pantropic and Specific Pathogens: Clinical Implications, Gene Transfer, Virulence Factors, and Future Perspectives

Mycoplasmas as economically important and pantropic pathogens can cause similar clinical diseases in different hosts by eluding host defense and establishing their niches despite their limited metabolic capacities. Besides, enormous undiscovered virulence has a fundamental role in the pathogenesis of pathogenic mycoplasmas. On the other hand, they are host-specific pathogens with some highly pathogenic members that can colonize a vast number of habitats. Reshuffling mycoplasmas genetic information and evolving rapidly is a way to avoid their host's immune system. However, currently, only a few control measures exist against some mycoplasmosis which are far from satisfaction. This review aimed to provide an updated insight into the state of mycoplasmas as pathogens by summarizing and analyzing the comprehensive progress, current challenge, and future perspectives of mycoplasmas. It covers clinical implications of mycoplasmas in humans and domestic and wild animals, virulence-related factors, the process of gene transfer and its crucial prospects, the current application and future perspectives of nanotechnology for diagnosing and curing mycoplasmosis, Mycoplasma vaccination, and protective immunity. Several questions remain unanswered and are recommended to pay close attention to. The findings would be helpful to develop new strategies for basic and applied research on mycoplasmas and facilitate the control of mycoplasmosis for humans and various species of animals.

Host cell interactions of novel antigenic membrane proteins of Mycoplasma agalactiae

Background

Mycoplasma agalactiae is the main etiological agent of Contagious Agalactia syndrome of small ruminants notifiable to the World Organization for Animal Health. Despite serious economic losses, successful vaccines are unavailable, largely because its colonization and invasion factors are not well understood. This study evaluates the role of two recently identified antigenic proteins (MAG_1560, MAG_6130) and the cytadhesin P40 in pathogenicity related phenotypes.

Results

Adhesion to HeLa and sheep primary mammary stromal cells (MSC) was evaluated using ELISA, as well as in vitro adhesion assays on monolayer cell cultures. The results demonstrated MAG_6130 as a novel adhesin of M. agalactiae whose capacity to adhere to eukaryotic cells was significantly reduced by specific antiserum. Additionally, these proteins exhibited significant binding to plasminogen and extracellular matrix (ECM) proteins like lactoferrin, fibrinogen and fibronectin, a feature that could potentially support the pathogen in host colonization, tissue migration and immune evasion. Furthermore, these proteins played a detrimental role on the host cell proliferation and viability and were observed to activate pro-apoptotic genes indicating their involvement in cell death when eukaryotic cells were infected with M. agalactiae.

Conclusions

To summarize, the hypothetical protein corresponding to MAG_6130 has not only been assigned novel adhesion functions but together with P40 it is demonstrated for the first time to bind to lactoferrin and ECM proteins thereby playing important roles in host colonization and pathogenicity.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12866-022-02512-2.

Molecular epidemiology and antimicrobials resistance mechanism of Mycoplasma genitlaium

Currently, infections caused by Mycoplasma genitalium are ones the most common sexually transmitted infections. Their prevalence is varied from 1.3% to 15.9%. Infections caused by M.genitalium may lead to urethritis in men and a wide spectrum of diseases in women. Antibiotic resistance now is one of the most emerging problems both in the scientific and in the healthcare fields. The usage of antimicrobials inhibiting cell wall synthesis for the treatment of M.genitalium is ineffective, and resistance to macrolides and fluoroquinolones is increasing rapidly. M.genitalium infections diagnostics is complicated due to specific conditions and duration of culture methods. The usage of nucleic acid amplification techniques is the most relevant for laboratory diagnostics, and is used in existing assays. This review compiles current data on the prevalence, molecular mechanisms of pathogenesis and antibiotic resistance, as well as diagnostics methods of M.genitalium.

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.

Single-Locus-Sequence-Based Typing of the mgpB Gene Reveals Transmission Dynamics in Mycoplasma genitalium

Sexually transmitted infections (STIs) by Mycoplasma genitalium are a major problem worldwide, especially given their marked and rapid propensity for developing antimicrobial resistance. Since very few treatment options exist, clinicians face an important challenge in the management of the infection. In this scenario, little is known regarding the transmission dynamics of M. genitalium and the epidemiology of antimicrobial resistance. This mgpB-based molecular typing study, conducted among 54 asymptomatically infected individuals prospectively recruited from an STI screening service, reveals two distinct epidemiological clusters that significantly correlate with sexual conduct in heterosexuals and men who have sex with men (MSM), respectively. This well-defined structuration suggests the presence of two independent sexual networks with little connectivity between them. On the other hand, the study demonstrates the multiclonal feature of the emergence of antibiotic resistance in M. genitalium to both macrolides and fluoroquinolones. The high prevalence of macrolide resistance in M. genitalium among MSM, influenced by dense network connectivity and strong antibiotic selective pressure, may correspond to allodemics affecting other STIs such as gonorrhea, syphilis and enteric pathogens. Collaterally, the structural and functional impact of mutations in the mgpB gene, encoding the major adhesin P140 (MgpB), may require further investigation.

MgpB Types among Mycoplasma genitalium Strains from Men Who Have Sex with Men in Berlin, Germany, 2016-2018

Mycoplasma genitalium is a cell wall-less bacterium causing urethritis and other sexually transmitted diseases. Despite a strongly conserved genome, strains in clinical samples can be typed by different methods. To obtain data from the risk population of men having sex with men, we analyzed the typing region in the gene coding for the MgpB adhesin of M. genitalium first in 163 and 45 follow-up samples among patients of two specialized practices in Berlin, Germany. Strains belong to 43 different mgpB types emphasizing the diversity of the genome region. With respect to 133 types previously described, 27 new types were found. However, the majority of strains (64.4%) were assigned to types 4, 6, 113, and 108, respectively. A correlation between mgpB type and the occurrence of mutations associated with macrolide and quinolone resistance was not demonstrated. Investigation of follow-up samples from 35 patients confirmed the same mgpB and, additionally, MG_309 types in 25 cases. In 10 cases, differences between types in subsequent samples indicated an infection with a genetically different strain in the period between samplings. MgpB/MG_309 typing is a useful method to compare M. genitalium strains in samples of individual patients as well as those circulating in different populations

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.

Comparative genomic analysis for nucleotide, codon, and amino acid usage patterns of mycoplasmas

The evolutionary factors in influencing the genetic characteristics of nucleotide, synonymous codon, and amino acid usage of 18 mycoplasma species were analyzed. The nucleotide usage at the 1st and 2nd codon position which determines amino acid composition of proteins has a significant correlation with the total nucleotide composition of gene population of these mycoplasma species, however, the nucleotide usage at the 3rd codon position which affects synonymous codon usage patterns has a slight correlation with either the total nucleotide composition or the nucleotide usage at the 1st and 2nd codon position. Other evolutionary factors join in the evolutionary process of mycoplasma apart from mutation pressure caused by nucleotide usage constraint based on the relationships between effective number of codons/codon adaptation index and nucleotide usage at the 3rd codon position. Although nucleotide usage of gene population in mycoplasma dominates in forming the overall codon usage trends, the relative abundance of codon with nucleotide context and amino acid usage pattern show that translation selection involved in translation accuracy and efficiency play an important role in synonymous codon usage patterns. In addition, synonymous codon usage patterns of gene population have a bigger power to represent genetic diversity among different species than amino acid usage. These results suggest that although the mycoplasmas reduce its genome size during the evolutionary process and shape the form, which is opposite to their hosts, of AT usages at high levels, this kind organism still depends on nucleotide usage at the 1st and 2nd codon positions to control syntheses of the requested proteins for surviving in their hosts and nucleotide usage at the 3rd codon position to develop genetic diversity of different mycoplasma species. This systemic analysis with 18 mycoplasma species may provide useful clues for further in vivo genetic studies on the related species.

Mycoplasma genitalium: whole genome sequence analysis, recombination and population structure

Background

Although Mycoplasma genitalium is a common sexually transmitted pathogen causing clinically distinct diseases both in male and females, few genomes have been sequenced up to now, due mainly to its fastidious nature and slow growth. Hence, we lack a robust phylogenetic framework to provide insights into the population structure of the species. Currently our understanding of the nature and diversity of M. genitalium relies on molecular tests targeting specific genes or regions of the genome and knowledge is limited by a general under-testing internationally. This is set against a background of drug resistance whereby M. genitalium has developed resistance to mainly all therapeutic antimicrobials.

Results

We sequenced 28 genomes of Mycoplasma genitalium from temporally (1980–2010) and geographically (Europe, Japan, Australia) diverse sources. All the strain showed essentially the same genomic content without any accessory regions found. However, we identified extensive recombination across their genomes with a total of 25 regions showing heightened levels of SNP density. These regions include the MgPar loci, associated with host interactions, as well as other genes that could also be involved in this role. Using these data, we generated a robust phylogeny which shows that there are two main clades with differing degrees of genomic variability. SNPs found in region V of 23S rRNA and parC were consistent with azithromycin/erythromycin and fluoroquinolone resistances, respectively, and with their phenotypic MIC data.

Conclusions

The sequence data here generated is essential for designing rational approaches to type and track Mycoplasma genitalium as antibiotic resistance increases. It represents a first approach to its population genetics to better appreciate the role of this organism as a sexually transmitted pathogen.

Electronic supplementary material

The online version of this article (10.1186/s12864-017-4399-6) contains supplementary material, which is available to authorized users.

Structural characterization of the NAP; the major adhesion complex of the human pathogen Mycoplasma genitalium

Mycoplasma genitalium, the causative agent of non-gonococcal urethritis and pelvic inflammatory disease in humans, is a small eubacterium that lacks a peptidoglycan cell wall. On the surface of its plasma membrane is the major surface adhesion complex, known as NAP that is essential for adhesion and gliding motility of the organism. Here, we have performed cryo-electron tomography of intact cells and detergent permeabilized M. genitalium cell aggregates, providing sub-tomogram averages of free and cell-attached NAPs respectively, revealing a tetrameric complex with two-fold rotational (C2) symmetry. Each NAP has two pairs of globular lobes (named α and β lobes), arranged as a dimer of heterodimers with each lobe connected by a stalk to the cell membrane. The β lobes are larger than the α lobes by 20%. Classification of NAPs showed that the complex can tilt with respect to the cell membrane. A protein complex containing exclusively the proteins P140 and P110, was purified from M. genitalium and was structurally characterized by negative-stain single particle EM reconstruction. The close structural similarity found between intact NAPs and the isolated P140/P110 complexes, shows that dimers of P140/P110 heterodimers are the only components of the extracellular region of intact NAPs in M. genitalium.