Type 1 and type 2 strains of Mycoplasma pneumoniae form different biofilms

Unravelling distinct patterns of metagenomic surveillance and respiratory microbiota between two P1 genotypes of Mycoplasma pneumoniae

To unravel distinct patterns of metagenomic surveillance and respiratory microbiota between Mycoplasma pneumoniae (M. pneumoniae) P1-1 and P1-2 and to explore the impact of the COVID-19 pandemic on epidemiological features, we conducted a multicentre retrospective study which spanned 90,886 pneumonia patients, among which 3164 cases M. pneumoniae were identified. Our findings revealed a concurrent outbreak of M. pneumoniae, with the positivity rate rising sharply to 9.62% from July 2023, compared to the 0.16% to 4.06% positivity rate observed during the 2020-2022 COVID-19 pandemic. P1-1 had a higher odds ratio of co-detecting opportunistic pathogens. However, no significant differences were observed in the co-detection odds ratio between children and other age groups in P1-2. This study is the first to demonstrate differences in relative abundance, diversity of respiratory microbiota and co-detection rate of opportunistic pathogen between M. pneumoniae P1-1 and P1-2. Through bronchoalveolar lavage (BAL) metagenomic and host transcriptomic analyses, we identified variations in co-detection rates of M. pneumoniae P1-1 genotype with opportunistic pathogens like S. pneumoniae, alterations in respiratory microbiota composition, lung inflammation, and disruption of ciliary function. Consistent with the results of host transcriptome, we found that P1-1 infections were associated with significantly higher rates of requiring respiratory support and mechanical ventilation compared to P1-2 infections (Fisher's exact test, p-value = 0.035/0.004). Our study provides preliminary evidence of clinical severity between M. pneumoniae strains, underscoring the need for ongoing research and development of targeted therapeutic strategies.

A diagnostic host-specific transcriptome response for Mycoplasma pneumoniae pneumonia to guide pediatric patient treatment

Mycoplasma pneumoniae causes atypical pneumonia in children and young adults. Its lack of a cell wall makes it resistant to beta-lactams, which are the first-line treatment for typical pneumonia. Current diagnostic tests are time-consuming and have low specificity, leading clinicians to administer empirical antibiotics. Using a LASSO regression simulation approach and blood microarray data from 107 children with pneumonia (including 30 M. pneumoniae) we identify eight different transcriptomic signatures, ranging from 3-10 transcripts, that differentiate mycoplasma pneumonia from other bacterial/viral pneumonias with high accuracy (AUC: 0.84-0.95). Additionally, we demonstrate that existing signatures for broadly distinguishing viral/bacterial infections and viral/bacterial pneumonias are ineffective in distinguishing M. pneumoniae from viral pneumonia. The new signatures are successfully validated in an independent RNAseq cohort of children with pneumonia, demonstrating their robustness. The high sensibility of these signatures presents a valuable opportunity to guide the treatment and management of M. pneumoniae pneumonia patients.

Global prevalence, resistance rates, and underlying resistance mechanisms of clinical Mycoplasma and Ureaplasma species

Mycoplasmas are significant pathogens in human health, implicated in a range of clinical conditions from respiratory infections to urogenital disorders. Their resistance to commonly used antibiotics poses a substantial challenge to treatment and control. This study aims to provide a comprehensive overview of the global distribution of clinical mycoplasmas, elucidate their resistance to various antibiotics, and identify the genetic and molecular mechanisms underlying their resistance. A systematic review and meta-analysis were conducted, collating data from peer-reviewed publications between 2012 and 2024. The UK (100%) and Germany (98%) reported high numbers of respiratory mycoplasmas, with 7% and 2% being resistant to macrolides. For urogenital mycoplasmas, Iceland (99%) and Estonia (94%) reported a high prevalence of Mycoplasma species, whereas the UK (85%), France (82%), and the USA (82%) reported a high prevalence of Ureaplasma species. High resistance rates in Mycoplasma and Ureaplasma have been reported in Greenland (100%) and the UK (86%), respectively. The rising resistance rates in these species underscore an urgent need for updated treatment guidelines and the development of novel therapeutic options. Our findings highlight the importance of tailored antibiotic stewardship and the potential of genomic insights in guiding effective treatment strategies.

Capsular Polysaccharide Production in Bacteria of the Mycoplasma Genus: A Huge Diversity of Pathways and Synthases for So-Called Minimal Bacteria

Mycoplasmas are wall-less bacteria with many species spread across various animal hosts in which they can be pathogenic. Despite their reduced anabolic capacity, some mycoplasmas are known to secrete hetero- and homopolysaccharides, which play a role in host colonization through biofilm formation or immune evasion, for instance. This study explores how widespread the phenomenon of capsular homopolysaccharide secretion is within mycoplasmas, and investigates the diversity of both the molecules produced and the synthase-type glycosyltransferases responsible for their production. Fourteen strains representing 14 (sub)species from four types of hosts were tested in vitro for their polysaccharide secretion using both specific (immunodetection) and nonspecific (sugar dosage) assays. We evidenced a new, atypical homopolymer of β-(1 → 6)-glucofuranose (named glucofuranan) in the human pathogen Mycoplasma (M.) fermentans, as well as a β-(1 → 6)-glucopyranose polymer for the turkey pathogen M. iowae and galactan (β-(1 → 6)-galactofuranose) and β-(1 → 2)-glucopyranose for M. bovigenitalium infecting ruminants. Sequence and phylogenetic analyses revealed a huge diversity of synthases from varied Mycoplasma species. The clustering of these membrane-embedded glycosyltransferases into three main groups was only partially correlated to the structure of the produced homopolysaccharides.

Mycoplasma pneumoniae: not a typical respiratory pathogen

Mycoplasma pneumoniae is a leading cause of community-acquired pneumonia among school-aged children and young adults. Infections occur throughout the year but tend to surge during winter months across Europe. A characteristic epidemic cycle, where a substantial surge in the number of infections occurs, is seen approximately every 1-4 years and hypothesized to be driven by changes in immunity and a shift in circulating variants. Once thought to be an organism of low virulence, it has now been found to possess several virulence factors, including toxin production, biofilm formation and evasion of antibody-mediated immunity. The lack of a cell wall and reduced metabolic pathways limit the options for antibiotic treatment. Acquired macrolide resistance is a growing concern, with >80% of cases in China being macrolide-resistant. Although efforts have been made to develop a vaccine, there are still substantial hurdles to overcome in relation to vaccine-enhanced disease, which results from an inappropriate immune response among vaccinated individuals.

Comparative genomic sequencing to characterize Mycoplasma pneumoniae genome, typing, and drug resistance

To analyze the characteristics of Mycoplasma pneumoniae as well as macrolide antibiotic resistance through whole-genome sequencing and comparative genomics. Thirteen clinical strains isolated from 2003 to 2019 were selected, 10 of which were resistant to erythromycin (MIC >64 µg/mL), including 8 P1-type I and 2 P1-type II. Three were sensitive (<1 µg/mL) and P1-type II. One resistant strain had an A→G point mutation at position 2064 in region V of the 23S rRNA, the others had it at position 2063, while the three sensitive strains had no mutation here. Genome assembly and comparative genome analysis revealed a high level of genome consistency within the P1 type, and the primary differences in genome sequences concentrated in the region encoding the P1 protein. In P1-type II strains, three specific gene mutations were identified: C162A and A430G in L4 gene and T1112G mutation in the CARDS gene. Clinical information showed seven cases were diagnosed with severe pneumonia, all of which were infected with drug-resistant strains. Notably, BS610A4 and CYM219A1 exhibited a gene multi-copy phenomenon and shared a conserved functional domain with the DUF31 protein family. Clinically, the patients had severe refractory pneumonia, with pleural effusion, necessitating treatment with glucocorticoids and bronchoalveolar lavage. The primary variations between strains occur among different P1-types, while there is a high level of genomic consistency within P1-types. Three mutation loci associated with specific types were identified, and no specific genetic alterations directly related to clinical presentation were observed.IMPORTANCEMycoplasma pneumoniae is an important pathogen of community-acquired pneumonia, and macrolide resistance brings difficulties to clinical treatment. We analyzed the characteristics of M. pneumoniae as well as macrolide antibiotic resistance through whole-genome sequencing and comparative genomics. The work addressed primary variations between strains that occur among different P1-types, while there is a high level of genomic consistency within P1-types. In P1-type II strains, three specific gene mutations were identified: C162A and A430G in L4 gene and T1112G mutation in the CARDS gene. All the strains isolated from severe pneumonia cases were drug-resistant, two of which exhibited a gene multi-copy phenomenon, sharing a conserved functional domain with the DUF31 protein family. Three mutation loci associated with specific types were identified, and no specific genetic alterations directly related to clinical presentation were observed.

Discovery of antimicrobial peptides in the global microbiome with machine learning

Novel antibiotics are urgently needed to combat the antibiotic-resistance crisis. We present a machine-learning-based approach to predict antimicrobial peptides (AMPs) within the global microbiome and leverage a vast dataset of 63,410 metagenomes and 87,920 prokaryotic genomes from environmental and host-associated habitats to create the AMPSphere, a comprehensive catalog comprising 863,498 non-redundant peptides, few of which match existing databases. AMPSphere provides insights into the evolutionary origins of peptides, including by duplication or gene truncation of longer sequences, and we observed that AMP production varies by habitat. To validate our predictions, we synthesized and tested 100 AMPs against clinically relevant drug-resistant pathogens and human gut commensals both in vitro and in vivo. A total of 79 peptides were active, with 63 targeting pathogens. These active AMPs exhibited antibacterial activity by disrupting bacterial membranes. In conclusion, our approach identified nearly one million prokaryotic AMP sequences, an open-access resource for antibiotic discovery.

Pathogenic avian mycoplasmas show phenotypic differences in their biofilm forming ability compared to non-pathogenic species in vitro

Mycoplasmas are known as the minimalist microorganisms in the microbes' world. Their minimalist nature makes them highly sensitive to the environmental conditions and limits their ability to survive for extended periods outside their animal host. Nevertheless, there are documented instances of mycoplasma transmission over significant distances and this phenomenon may be linked to relatively unexplored abilities of mycoplasmas, such as their capacity to synthesize biofilm-the predominant mode of bacterial growth in nature. The authors decided to establish a method aimed at inducing the clustering of mycoplasma planktonic cells within a biofilm in vitro and subsequently assess the capacity of certain avian mycoplasmas to synthesize a biofilm. A total of 299 avian mycoplasma isolates were included in the study, encompassing both pathogenic (Mycoplasma gallisepticum, M. synoviae, M. meleagridis, M. iowae) and non-pathogenic species (M. gallinaceum, M. gallinarum, M. iners and M. pullorum). The authors successfully demonstrated the feasibility of inducing avian mycoplasmas to synthetize in vitro a biofilm, which can be visually quantified. The only species that did not produce any biofilm was M. iowae. In general, the pathogenic mycoplasmas produced greater quantities of biofilm compared to the non-pathogenic ones. Furthermore, it was observed that the ability to produce biofilm appeared to vary, both qualitatively and quantitatively, not only among different species but also among isolates of a single species. Future studies will be necessary to determine whether biofilm production plays a pivotal epidemiological role for the pathogenic avian mycoplasmas.

Computational exploration of the global microbiome for antibiotic discovery

Novel antibiotics are urgently needed to combat the antibiotic-resistance crisis. We present a machine learning-based approach to predict prokaryotic antimicrobial peptides (AMPs) by leveraging a vast dataset of 63,410 metagenomes and 87,920 microbial genomes. This led to the creation of AMPSphere, a comprehensive catalog comprising 863,498 non-redundant peptides, the majority of which were previously unknown. We observed that AMP production varies by habitat, with animal-associated samples displaying the highest proportion of AMPs compared to other habitats. Furthermore, within different human-associated microbiota, strain-level differences were evident. To validate our predictions, we synthesized and experimentally tested 50 AMPs, demonstrating their efficacy against clinically relevant drug-resistant pathogens both in vitro and in vivo. These AMPs exhibited antibacterial activity by targeting the bacterial membrane. Additionally, AMPSphere provides valuable insights into the evolutionary origins of peptides. In conclusion, our approach identified AMP sequences within prokaryotic microbiomes, opening up new avenues for the discovery of antibiotics.

The Association between Mycoplasma pneumoniae Genotype and Cutaneous Disease

Mycoplasma pneumoniae (Mp) can cause several extrapulmonary manifestations, most frequently dermatological ones. It is largely unknown whether Mp genotype determines Mp-induced cutaneous disease. The aim of our study was to assess the association between Mp genotype and this clinical outcome. We performed a retrospective study of children referred with signs of acute Mp infection from 1 January 2014 to 31 December 2014. We compared the characteristics of children presenting as cutaneous disease, upper (URTI) and lower respiratory tract infection (LRTI). In addition, we separately analyzed the data of patients presenting with Mp-induced cutaneous disease. We evaluated data from 435 patients (mean age 7.3 years, SD 3.4 years; 52.0% boys) who had Mp PCR-positive pharyngeal swab, P1 genotype and/or multilocus variable-number tandem-repeat analysis (MLVA) genotype defined and no viral co-detection, presenting as cutaneous disease (38/435), URTI (46/435) or LRTI (351/435). The majority of patients had urticarial (55%, 21/38) or maculopapular eruptions (37%, 14/38). We found no association between Mp genotype and clinical outcome of cutaneous disease, nor any specific dermatological presentation. In the group with cutaneous disease, 18% (7/38) required hospital admission because of rash. We found that infection with MLVA-3,6,6,2 strains was more common in admitted patients than in outpatients (40% vs. 4%, p = 0.017) and significantly affected the likelihood of hospital admission in a logistic regression model. The results of our cohort study suggest that Mp genotype does not determine Mp-induced cutaneous disease or a specific dermatological presentation. Nevertheless, infections with certain MLVA strains could induce more severe cutaneous disease requiring hospitalization.

Mycoplasma pneumoniae downregulates RECK to promote matrix metalloproteinase-9 secretion by bronchial epithelial cells

Airway epithelial cells function as both a physical barrier against harmful substances and pathogenic microorganisms and as an important participant in the innate immune system. Matrix metalloproteinase-9 (MMP-9) plays a crucial role in modulating inflammatory responses during respiratory infections. However, the signalling cascade that induces MMP-9 secretion from epithelial cells infected with Mycoplasma pneumoniae remains poorly understood. In this study, we investigated the mechanism of MMP-9 secretion in airway epithelial cells infected with M. pneumoniae. Our data clearly showed that M. pneumoniae induced the secretion of MMP-9 from bronchial epithelial cells and upregulated its enzymatic activity in a time- and dose-dependent manner. Using specific inhibitors and chromatin co-precipitation experiments, we confirmed that the expression of MMP-9 is reliant on the activation of the Toll-like receptor 2 (TLR2) and TLR6-dependent mitogen-activated protein kinase/nuclear factor- κB/activator protein-1 (MAPK/NF-κB/AP-1) pathways. Additionally, epigenetic modifications such as histone acetylation and the nuclear transcription factor Sp1 also regulate MMP-9 expression. M. pneumoniae infection also decreased the expression of the tumour suppressor reversion-inducing cysteine-rich protein with Kazal motifs (RECK) by inducing Sp1 phosphorylation. Overexpression of RECK significantly impaired the M. pneumoniae-triggered increase in MMP-9 enzymatic activity, although the level of MMP-9 protein remained constant. The study demonstrated that M. pneumoniae-triggered MMP-9 expression is modulated by TLR2 and 6, the MAPK/NF-κB/AP-1 signalling cascade, and histone acetylation, and M. pneumoniae downregulated the expression of RECK, thereby increasing MMP-9 activity to modulate the inflammatory response, which could play a role in airway remodelling.

Cell shape controls rheotaxis in small parasitic bacteria

Mycoplasmas, a group of small parasitic bacteria, adhere to and move across host cell surfaces. The role of motility across host cell surfaces in pathogenesis remains unclear. Here, we used optical microscopy to visualize rheotactic behavior in three phylogenetically distant species of Mycoplasma using a microfluidic chamber that enabled the application of precisely controlled fluid flow. We show that directional movements against fluid flow occur synchronously with the polarized cell orienting itself to be parallel against the direction of flow. Analysis of depolarized cells revealed that morphology itself functions as a sensor to recognize rheological properties that mimic those found on host-cell surfaces. These results demonstrate the vital role of cell morphology and motility in responding to mechanical forces encountered in the native environment.

The small, parasitic bacterium Mycoplasma pneumoniae attaches to, and moves over, host cell surfaces. Adherence to host surfaces and motility are critical for the pathogenicity of M. pneumoniae. The role of motility by M. pneumoniae in vivo, however, is poorly understood. Host airways generate constant fluid flow toward the mouth as part of their defense against pathogens and irritants. Consequently, pulmonary invaders must counter the rheological forces found in host airways in order to successfully colonize the host. Here, we demonstrate that M. pneumoniae exhibits directional movement against fluid flow. These findings suggest there is a vital role for rheotactic motility that has evolved in order to overcome host defense mechanisms such as mucociliary clearance.

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.

The Mycoplasma spp. ‘Releasome’: A New Concept for a Long-Known Phenomenon

The bacterial secretome comprises polypeptides expressed at the cell surface or released into the extracellular environment as well as the corresponding secretion machineries. Despite their reduced coding capacities, Mycoplasma spp. are able to produce and release several components into their environment, including polypeptides, exopolysaccharides and extracellular vesicles. Technical difficulties in purifying these elements from the complex broth media used to grow mycoplasmas have recently been overcome by optimizing growth conditions and switching to chemically defined culture media. However, the secretion pathways responsible for the release of these structurally varied elements are still poorly described in mycoplasmas. We propose the use of the term ‘releasome,’ instead of secretome, to refer to molecules released by mycoplasmas into their environment. The aim of this review is to more precisely delineate the elements that should be considered part of the mycoplasmal releasome and their role in the interplay of mycoplasmas with host cells and tissues.

Community-Acquired Respiratory Distress Syndrome Toxin: Unique Exotoxin for M. pneumoniae

Mycoplasma pneumoniae infection often causes respiratory diseases in humans, particularly in children and adults with atypical pneumonia and community-acquired pneumonia (CAP), and is often exacerbated by co-infection with other lung diseases, such as asthma, bronchitis, and chronic obstructive pulmonary disorder. Community-acquired respiratory distress syndrome toxin (CARDS TX) is the only exotoxin produced by M. pneumoniae and has been extensively studied for its ADP-ribosyltransferase (ADPRT) activity and cellular vacuolization properties. Additionally, CARDS TX induces inflammatory responses, resulting in cell swelling, nuclear lysis, mucus proliferation, and cell vacuolization. CARDS TX enters host cells by binding to the host receptor and is then reverse transported to the endoplasmic reticulum to exert its pathogenic effects. In this review, we focus on the structural characteristics, functional activity, distribution and receptors, mechanism of cell entry, and inflammatory response of CARDS TX was examined. Overall, the findings of this review provide a theoretical basis for further investigation of the mechanism of M. pneumoniae infection and the development of clinical diagnosis and vaccines.

Pathogenicity & virulence of Mycoplasma hyopneumoniae

Mycoplasma hyopneumoniae: is the etiological agent of porcine enzootic pneumonia (EP), a disease that impacts the swine industry worldwide. Pathogen-induced damage, as well as the elicited host-response, contribute to disease. Here, we provide an overview of EP epidemiology, control and prevention, and a more in-depth review of M. hyopneumoniae pathogenicity determinants, highlighting some molecular mechanisms of pathogen-host interactions relevant for pathogenesis. Based on recent functional, immunological, and comparative “omics” results, we discuss the roles of many known or putative M. hyopneumoniae virulence factors, along with host molecules involved in EP. Moreover, the known molecular bases of pathogenicity mechanisms, including M. hyopneumoniae adhesion to host respiratory epithelium, protein secretion, cell damage, host microbicidal response and its modulation, and maintenance of M. hyopneumoniae homeostasis during infection are described. Recent findings regarding M. hyopneumoniae pathogenicity determinants also contribute to the development of novel diagnostic tests, vaccines, and treatments for EP.

Mycoplasma pneumoniae P1 Genotype Indicates Severity of Lower Respiratory Tract Infections in Children

Mycoplasma pneumoniae strains can be classified into two major genetic groups, P1 type 1 (P1-1) and P1 type 2 (P1-2). It remains unknown if clinical manifestations of lower respiratory tract infections (LRTI) in children differ between the two genotypes. We aimed to determine if the M. pneumoniae P1 genotype is associated with severity of LRTI in children. Medical charts of 420 children (≤15 years old) with signs of acute LRTI who were PCR positive for M. pneumoniae from pharyngeal swabs in a recent M. pneumoniae epidemic were analyzed. We used a culture and pyrosequencing approach for genotyping PCR-positive samples. We compared epidemiological and clinical data of children with either P1-1 or P1-2 LRTI. P1-2-infected children presented with a significantly higher median baseline C-reactive protein level and were admitted to the hospital more often. The P1 genotype had a significant predictive value in a multiple linear regression model predicting C-reactive protein levels in our study sample. Moreover, the P1 genotype significantly affected the likelihood of hospital admission in a logistic regression model. Our modeling results were also confirmed on an additional independent sample of children with M. pneumoniae LRTI. Results from our large patient group indicate that the two M. pneumoniae P1 genotypes may have different pathogenic potential and that LRTI with P1-2 strains may have a more severe disease course than those with P1-1 strains in children. P1 genotyping is not routinely performed but could be used as a predictor of M. pneumoniae LRTI severity, enabling patient-tailored treatments.

Mycoplasma pneumoniae biofilms grown in vitro: traits associated with persistence and cytotoxicity

The atypical bacterial pathogen Mycoplasma pneumoniae is a leading etiological agent of community-acquired pneumonia in humans; infections are often recalcitrant, recurrent and resistant to antibiotic treatment. These characteristics suggest a mechanism that facilitates long-term colonization in hosts. In an in vitro setting, M. pneumoniae forms biofilms that are unusual in that motility plays no more than a very limited role in their formation and development. Given the unusual nature of M. pneumoniae biofilms, open questions remain concerning phenotypes associated with persistence, such as what properties might favour the bacteria while minimizing host damage. M. pneumoniae also produces several cytotoxic molecules including community-acquired respiratory distress syndrome (CARDS) toxin, H₂S and H₂O₂, but how it deploys these agents during growth is unknown. Whereas several biochemical techniques for biofilm disruption were ineffective, sonication was required for disruption of M. pneumoniae biofilms to generate individual cells for comparative studies, suggesting unusual physical properties likely related to the atypical cell envelope. Nonetheless, like for other bacteria, biofilms were less susceptible to antibiotic inhibition and complement killing than dispersed cells, with resistance increasing as the biofilms matured. CARDS toxin levels and enzymatic activities associated with H₂S and H₂O₂ production were highest during early biofilm formation and decreased over time, suggesting attenuation of virulence in connection with chronic infection. Collectively, these findings result in a model of how M. pneumoniae biofilms contribute to both the establishment and propagation of M. pneumoniae infections, and how both biofilm towers and individual cells participate in persistence and chronic disease.

Visualisation and biovolume quantification in the characterisation of biofilm formation in Mycoplasma fermentans

The ability of mycoplasmas to persist on surfaces has been widely acknowledged, despite their fastidious nature. However, the organism's capability to form a recognisable biofilm structure has been identified more recently. In the current study Mycoplasma fermentans was found to adhere to the glass surface forming highly differentiated biofilm structures. The volumes of biofilm microcolonies were quantified and observed to be greater at late growth stage than those at early growth stage. The channel diameters within biofilms were measured with Scanning Electron Microscopy images and found to be consistent with the size observed in Confocal Laser Scanning Microscope images. The combination of imaging methods with 3D visualisation provides key findings that aid understanding of the mycoplasma biofilm formation and true biofilm architecture. The observations reported here provide better understanding of the persistence of these minimalist pathogens in nature and clinical settings.

A requirement for flow to enable the development of Ureaplasma parvum biofilms in vitro

AIMS

To use a flow-based method to establish, quantify and visualize biofilms of Ureaplasma parvum.

METHODS AND RESULTS

Absorbance readings of a U. parvum HPA5 culture were taken at 550 nm every 3 h for 30 h in order to establish a growth curve, with viability determined by the number of colour changing units (CCUs). Biofilms were established using the DTU flow-cell with a flow rate of 0·01 ml min^-1 and compared to the static control. Titres of bacteria were determined by CCU and biofilm biomass was quantified by Syto9 staining and COMSTAT analysis. High-resolution images were obtained by scanning electron microscopy (SEM). Flow resulted in significantly more biofilm and higher cell titre (0·599 µm³ /µm²  ± 0·152 and 4 × 10⁸  CCU per ml, respectively) compared with static conditions (0·008 µm³ /µm²  ± 0·010 and no recoverable cells, respectively). SEM revealed pleomorphic cells, with signs of budding and possible membrane vesicle formation.

CONCLUSIONS

Flow is an essential requirement for the establishment of U. parvum biofilms.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first quantification of biofilm biomass formed by U. parvum. It is now possible to establish viable biofilms of U. parvum which will allow for future testing of antimicrobial agents and understanding of virulence-associated with adhesion.

Infection strategies of mycoplasmas: Unraveling the panoply of virulence factors

Mycoplasmas, the smallest bacteria lacking a cell wall, can cause various diseases in both humans and animals. Mycoplasmas harbor a variety of virulence factors that enable them to overcome numerous barriers of entry into the host; using accessory proteins, mycoplasma adhesins can bind to the receptors or extracellular matrix of the host cell. Although the host immune system can eradicate the invading mycoplasma in most cases, a few sagacious mycoplasmas employ a series of invasion and immune escape strategies to ensure their continued survival within their hosts. For instance, capsular polysaccharides are crucial for anti-phagocytosis and immunomodulation. Invasive enzymes degrade reactive oxygen species, neutrophil extracellular traps, and immunoglobulins. Biofilm formation is important for establishing a persistent infection. During proliferation, successfully surviving mycoplasmas generate numerous metabolites, including hydrogen peroxide, ammonia and hydrogen sulfide; or secrete various exotoxins, such as community-acquired respiratory distress syndrome toxin, and hemolysins; and express various pathogenic enzymes, all of which have potent toxic effects on host cells. Furthermore, some inherent components of mycoplasmas, such as lipids, membrane lipoproteins, and even mycoplasma-generated superantigens, can exert a significant pathogenic impact on the host cells or the immune system. In this review, we describe the proposed virulence factors in the toolkit of notorious mycoplasmas to better understand the pathogenic features of these bacteria, along with their pathogenic mechanisms.

Modelling persistent Mycoplasma pneumoniae biofilm infections in a submerged BEAS-2B bronchial epithelial tissue culture model

Introduction. Infections with the respiratory pathogen Mycoplasma pneumoniae are often chronic, recurrent and resistant, persisting after antibiotic treatment. M. pneumoniae grown on glass forms protective biofilms, consistent with a role for biofilms in persistence. These biofilms consist of towers of bacteria interspersed with individual adherent cells.Hypothesis/Gap Statement. A tissue culture model for M. pneumoniae biofilms has not been described or evaluated to address whether growth, development and resistance properties are consistent with persistence in the host. Moreover, it is unclear whether the M. pneumoniae cells in the biofilm towers and individual bacterial cells have distinct roles in disease.Aim. We evaluated the properties of biofilms of M. pneumoniae grown on the immortalized human bronchial epithelial cell line BEAS-2B in relation to persistence in the host. We observed nucleation of biofilm towers and the disposition of individual cells in culture, leading to a model of how tower and individual cells contribute to infection and disease.Methodology. With submerged BEAS-2B cells as a substrate, we evaluated growth and development of M. pneumoniae biofilms using scanning electron microscopy and confocal laser scanning microscopy. We characterized resistance to erythromycin and complement using minimum inhibitory concentration assays and quantification of colony forming units. We monitored biofilm tower formation using time-lapse microscopic analysis of host-cell-free M. pneumoniae cultures.Results. Bacteria grown on host cells underwent similar development to those grown without host cells, including tower formation, rounding and incidence of individual cells outside towers. Erythromycin and complement significantly reduced growth of M. pneumoniae. Towers formed exclusively from pre-existing aggregates of bacteria. We discuss a model of the M. pneumoniae biofilm life cycle in which protective towers derive from pre-existing aggregates, and generate individual cytotoxic cells.Conclusion . M. pneumoniae can form protective biofilms in a tissue culture model, implicating biofilms in chronic infections, with aggregates of M. pneumoniae cells being important for establishing infections.

Mycoplasma pneumoniae Infections: Pathogenesis and Vaccine Development

Mycoplasma pneumoniae is a major causative agent of community-acquired pneumonia which can lead to both acute upper and lower respiratory tract inflammation, and extrapulmonary syndromes. Refractory pneumonia caused by M. pneumonia can be life-threatening, especially in infants and the elderly. Here, based on a comprehensive review of the scientific literature related to the respective area, we summarize the virulence factors of M. pneumoniae and the major pathogenic mechanisms mediated by the pathogen: adhesion to host cells, direct cytotoxicity against host cells, inflammatory response-induced immune injury, and immune evasion. The increasing rate of macrolide-resistant strains and the harmful side effects of other sensitive antibiotics (e.g., respiratory quinolones and tetracyclines) in young children make it difficult to treat, and increase the health risk or re-infections. Hence, there is an urgent need for development of an effective vaccine to prevent M. pneumoniae infections in children. Various types of M. pneumoniae vaccines have been reported, including whole-cell vaccines (inactivated and live-attenuated vaccines), subunit vaccines (involving M. pneumoniae protein P1, protein P30, protein P116 and CARDS toxin) and DNA vaccines. This narrative review summarizes the key pathogenic mechanisms underlying M. pneumoniae infection and highlights the relevant vaccines that have been developed and their reported effectiveness.

Mycoplasma genitalium Biofilms Contain Poly-GlcNAc and Contribute to Antibiotic Resistance

Mycoplasma genitalium is an important etiologic agent of non-gonococcal urethritis (NGU), known for chronicity and multidrug resistance, in which biofilms may play an integral role. In some bacterial species capable of forming biofilms, extracellular polymeric substances (EPS) composed of poly-N-acetylglucosamine (PNAG) are a crucial component of the matrix. Monosaccharide analysis of M. genitalium strains revealed high abundance of GlcNAc, suggesting a biofilm-specific EPS. Chromatograms also showed high concentrations of galactose and glucose as observed in other mycoplasma species. Fluorescence microscopy of M. genitalium biofilms utilizing fluor-coupled lectins revealed differential staining of biofilm structures. Scanning electron microscopy (SEM) showed increasing maturation over time of bacterial “towers” seen in biofilm development. As seen with Mycoplasma pneumoniae, organisms within fully mature M. genitalium biofilms exhibited loss of cell polarization. Bacteria associated with disrupted biofilms exhibited decreased dose-dependent viability after treatment with antibiotics compared to bacteria with intact biofilms. In addition, growth index analysis demonstrated decreases in metabolism in cultures with disrupted biofilms with antibiotic treatment. Taken together, these data suggest that M. genitalium biofilms are a contributing factor in antibiotic resistance.

Diversity in Genotype Distribution of Mycoplasma pneumoniae Obtained from Children and Adults

The aim of this study was to explore whether there was any specific genotype responsible for the high prevalence of Mycoplasma pneumoniae infection in children. A total of 247 M. pneumoniae-DNA positive clinical specimens including 200 from children and 47 from adults, collected in Beijing, China, during the same period, were analyzed. We performed P1-restriction fragment length polymorphism analysis (RFLP), multi-locus variable number tandem repeat analysis (MLVA) and detected the macrolide resistance-associated mutations in 23S rRNA of the clinical specimens. In the present study, we observed P1 genotype 1 and MLVA type M4-5-7-2 accounted for the majority of the cases across all ages in Beijing. Macrolide resistance-associated mutants of M. pneumoniae were also at a high level with 90.5% (181/200) in children and 76.6% (36/47) in adults. However, more diverse genotypes and a higher prevalence of macrolide resistance-associated mutations were found in the pediatric specimens. Further investigations are warranted to help to explain the difference of morbidity and molecular characteristics across the demographic spectrum.

Subversion of the Immune Response by Human Pathogenic Mycoplasmas

Mycoplasmas are a large group of prokaryotes which is believed to be originated from Gram-positive bacteria via degenerative evolution, and mainly capable of causing a wide range of human and animal infections. Although innate immunity and adaptive immunity play crucial roles in preventing mycoplasma infection, immune response that develops after infection fails to completely eliminate this bacterium under certain circumstances. Thus, it is reasonable to speculate that mycoplasmas employ some mechanisms to deal with coercion of host defense system. In this review, we will highlight and provide a comprehensive overview of immune evasion strategies that have emerged in mycoplasma infection, which can be divided into four aspects: (i) Molecular mimicry and antigenic variation on the surface of the bacteria to evade the immune surveillance; (ii) Overcoming the immune effector molecules assaults: Induction of detoxified enzymes to degradation of reactive oxygen species; Expression of nucleases to degrade the neutrophil extracellular traps to avoid killing by Neutrophil; Capture and cleavage of immunoglobulins to evade humoral immune response; (iii) Persistent survival: Invading into the host cell to escape the immune damage; Formation of a biofilm to establish a persistent infection; (iv) Modulation of the immune system to down-regulate the intensity of immune response. All of these features increase the probability of mycoplasma survival in the host and lead to a persistent, chronic infections. A profound understanding on the mycoplasma to subvert the immune system will help us to better understand why mycoplasma is so difficult to eradicate and ultimately provide new insights on the development of therapeutic regimens against this bacterium in future.

Molecular and clinical characteristics of severe Mycoplasma pneumoniae pneumonia in children

OBJECTIVES

To analyze the molecular and the clinical characteristics of Mycoplasma pneumoniae (Mp) pneumonia (MPP) and to explore the related factors predicting severe MPP (SMPP).

METHODS

A total of 423 pediatric cases of MPP were retrospectively analyzed, in 2013-2017, in Beijing, China. Clinical information was collected from the medical records. Mp-positive specimens were characterized using P1 typing and multiple locus variable-number tandem repeat analysis (MLVA). The macrolide resistance-associated mutations were also detected.

RESULTS

The predominant genotype was P1-1 (88.2%) and M4-5-7-2 (87.5%), whereas percentages of type P1-2 and M3-5-6-2 increased across the 5-year period. The mutation rate of genotype M4-5-7-2 (365/370, 98.6%) was significantly higher than that of the genotype M3-5-6-2 (15/48, 32.25%; P = 0.000). Overall, 180 (42.6%) of the 423 Mp-positive patients were coinfected with other pathogens. Respiratory syncytial virus coinfection (24/180, 13.3%) was more common in cases typed M3-5-6-2 (4/23, 17.4%) than that of M4-5-7-2 (20/155, 12.9%; P = 0.038). Pleural effusion accounted for 52.6% (169/321) of the observed complications. In the mono-infection cases, cases typed M3-5-6-2 (56%, 14/25) were significantly (P = 0.020) associated with pleural effusion compared with those typed M4-5-7-2 (32.6%, 70/215); 84% (21/25) of specimens typed M3-5-6-2 were diagnosed as SMPP, whereas 63.7% (137/215) of specimens typed M4-5-7-2 were diagnosed as SMPP (P = 0.043).

CONCLUSIONS

In our study, we proposed for the first time that the mono-infection patients with Mp typed M3-5-6-2 appear to have a higher risk for progressing to SMPP. MLVA typing can provide hints on the clinical characteristics of Mpp.

Molecular Typing of Mycoplasma pneumoniae Strains in Sweden from 1996 to 2017 and the Emergence of a New P1 Cytadhesin Gene, Variant 2e

Mycoplasma pneumoniae causes respiratory infections, such as community-acquired pneumonia (CAP), with epidemics recurring every 3 to 7 years. In 2010 and 2011, many countries experienced an extraordinary epidemic peak.

Mycoplasma pneumoniae causes respiratory infections, such as community-acquired pneumonia (CAP), with epidemics recurring every 3 to 7 years. In 2010 and 2011, many countries experienced an extraordinary epidemic peak. The cause of these recurring epidemics is not understood, but decreasing herd immunity and shifts in the strains’ antigenic properties have been suggested as contributing factors. M. pneumoniae PCR-positive samples were collected between 1996 and 2017 from four neighboring counties inhabited by 12% of Sweden’s population. A total of 578 isolates were characterized directly from 624 clinical samples using P1 typing by sequencing and multilocus variable number tandem repeat analysis (MLVA). A fluorescence resonance energy transfer (FRET)-PCR approach was also used to detect mutations associated with macrolide resistance in the 23S rRNA gene. Through P1 typing, the strains were classified into type 1 and type 2, as well as variants 2a, 2b, 2c, and a new variant found in nine of the strains, denoted variant 2e. Twelve MLVA types were distinguished, and 3-5-6-2 (42.4%), 4-5-7-2 (37.4%), and 3-6-6-2 (14.9%) predominated. Several P1 and MLVA types cocirculated each year, but type 2/variant 2 strains and MLVA types 3-5-6-2 and 4-5-7-2 predominated during the epidemic period comprising the peak of 2010 and 2011. In 2016 and 2017, type 1 became more common, and MLVA type 4-5-7-2 predominated. We also found that 0.2% (1/578) of the strains carried a macrolide resistance-associated mutation, indicating a very low prevalence of macrolide resistance in this region of Sweden.

Turning the Tide against Antibiotic Resistance by Evaluating Novel, Halogenated Phenazine, Quinoline, and NH125 Compounds against Ureaplasma Species Clinical Isolates and Mycoplasma Type Strains

Escalating levels of antibiotic resistance in mycoplasmas, particularly macrolide resistance in Mycoplasma pneumoniae and M. genitalium, have narrowed our antibiotic arsenal. Further, mycoplasmas lack a cell wall and do not synthesize folic acid, rendering common antibiotics, such as beta-lactams, vancomycin, sulfonamides, and trimethoprim, of no value.

Escalating levels of antibiotic resistance in mycoplasmas, particularly macrolide resistance in Mycoplasma pneumoniae and M. genitalium, have narrowed our antibiotic arsenal. Further, mycoplasmas lack a cell wall and do not synthesize folic acid, rendering common antibiotics, such as beta-lactams, vancomycin, sulfonamides, and trimethoprim, of no value. To address this shortage, we screened nitroxoline, triclosan, and a library of 20 novel, halogenated phenazine, quinoline, and NH125 analogues against Ureaplasma species and M. hominis clinical isolates from urine. We tested a subset of these compounds (n = 9) against four mycoplasma type strains (M. pneumoniae, M. genitalium, M. hominis, and Ureaplasma urealyticum) using a validated broth microdilution or agar dilution method. Among 72 Ureaplasma species clinical isolates, nitroxoline proved most effective (MIC₉₀, 6.25 µM), followed by an N-arylated NH125 analogue (MIC₉₀, 12.5 µM). NH125 and its analogue had significantly higher MICs against U. urealyticum isolates than against U. parvum isolates, whereas nitroxoline did not. Nitroxoline exhibited bactericidal activity against U. parvum isolates but bacteriostatic activity against the majority of U. urealyticum isolates. Among the type strains, the compounds had the greatest activity against M. pneumoniae and M. genitalium, with 8 (80%) and 5 (71.4%) isolates demonstrating MICs of ≤12.5 µM, respectively. Triclosan also exhibited lower MICs against M. pneumoniae and M. genitalium. Overall, we identified a promising range of quinoline, halogenated phenazine, and NH125 compounds that showed effectiveness against M. pneumoniae and M. genitalium and found that nitroxoline, approved for use outside the United States for the treatment of urinary tract infections, and an N-arylated NH125 analogue demonstrated low MICs against Ureaplasma species isolates.

Positively interacting strains that co-circulate within a network structured population induce cycling epidemics of Mycoplasma pneumoniae

Mycoplasma pneumoniae (MP) is considered a common cause of pneumonia, causing about 15–20% of adult community-acquired pneumonia (CAP) and up to 40% of cases in children. It has often been observed that MP epidemics last approximately 1–2 years and occur every 3–7 years, with the dominant strains alternating between epidemics. However, the underlying mechanism by which these cycles and changes in the dominant strains occur remains unclear. The traditional models for the periodicity of MP epidemics neglected two phenomena: structured contact patterns among people and co-circulating strains of MP. We also believe that the two distinctive aspects of MP epidemics: prevalent serotype shifts among epidemics and incidence cycling of MP, are interconnected. We propose a network transmission model that assumes two strains of MP are transmitted within a network structured population and they can interact as secondary infections with primary infections. Our studies show that multiple strains that co-circulate within a network structured population and interact positively generate the observed patterns of recurrent epidemics of MP. Hence our study provides a possible mechanism for the cycling epidemics of MP, and could provide useful information for future vaccine design and vaccine evaluation/monitoring processes.

Mycoplasma pneumoniae Pneumonia with Worsening Pleural Effusion Despite Treatment with Appropriate Antimicrobials: Case report

Mycoplasma pneumoniae is a common cause of community-acquired pneumonia. As M. pneumoniae pneumonia is usually a mild and self-limiting disease, complications such as pleural effusion occur only rarely. We report a 22-year-old woman who presented to the Emergency Medicine Department of the Sultan Qaboos University Hospital, Muscat, Oman, in 2017 with an eight-day history of fever associated with coughing, chills and rigors. She was diagnosed with M. pneumoniae pneumonia, but subsequently developed pleural effusion which worsened despite treatment with appropriate antimicrobials. The pleural effusion required drainage, which revealed that it was of the more severe exudative type. Following drainage, the patient improved dramatically. She was discharged and advised to continue taking antibiotics.

Extracellular DNA release from the genome-reduced pathogen Mycoplasma hyopneumoniae is essential for biofilm formation on abiotic surfaces

Mycoplasma hyopneumoniae is an economically devastating, globally disseminated pathogen that can maintain a chronic infectious state within its host, swine. Here, we depict the events underpinning M. hyopneumoniae biofilm formation on an abiotic surface and demonstrate for the first time, biofilms forming on porcine epithelial cell monolayers and in the lungs of pigs, experimentally infected with M. hyopneumoniae. Nuclease treatment prevents biofilms forming on glass but not on porcine epithelial cells indicating that extracellular DNA (eDNA), which localises at the base of biofilms, is critical in the formation of these structures on abiotic surfaces. Subpopulations of M. hyopneumoniae cells, denoted by their ability to take up the dye TOTO-1 and release eDNA, were identified. A visually distinct sub-population of pleomorphic cells, that we refer to here as large cell variants (LCVs), rapidly transition from phase dark to translucent "ghost" cells. The translucent cells accumulate the membrane-impermeable dye TOTO-1, forming readily discernible membrane breaches immediately prior to lysis and the possible release of eDNA and other intracellular content (public goods) into the extracellular environment. Our novel observations expand knowledge of the lifestyles adopted by this wall-less, genome-reduced pathogen and provide further insights to its survival within farm environments and swine.

Clinical characteristics of infections caused by Mycoplasma pneumoniae P1 genotypes in children

Mycoplasma pneumoniae (M. pneumoniae) isolates can be classified into two major genetic groups, P1 type 1 (MP1) and P1 type 2 (MP2), based on the DNA sequence of the P1 adhesion protein gene. The aim of our study was to determine if M. pneumoniae P1 genotype is associated with disease manifestation and severity of acute M. pneumoniae infection. We compared epidemiological and clinical data of children infected with either MP1 or MP2. In addition, we separately analysed data of patients presenting with individual manifestations of M. pneumoniae infection. Data of 356 patients infected with MP1 were compared with those of 126 patients infected with MP2. MP2-infected children presented with higher median baseline C-reactive protein levels and were admitted to the hospital more often. The distribution of P1 genotype varied among groups of patients with different manifestations of M. pneumoniae infection. MP2 was more common than MP1 among patients with neurological and cardiovascular manifestations, whereas MP1 was more prevalent in other manifestations. The results from our large cohort indicate that the two P1 subtypes may have different pathogenic potential and that infections with MP2 strains could be more virulent than those with MP1 strains.

Gap analysis of Mycoplasma bovis disease, diagnosis and control: An aid to identify future development requirements

There is a worldwide problem of disease caused by Mycoplasma (M.) bovis in cattle; it has a significant detrimental economic and animal welfare impact on cattle rearing. Infection can manifest as a plethora of clinical signs including mastitis, pneumonia, arthritis, keratoconjunctivitis, otitis media and genital disorders that may result in infertility and abortion. Current diagnosis and control information are reviewed and analysed to identify gaps in knowledge of the causative organism in respect of the disease pathology, diagnosis and control methods. The main considerations are as follows: no vaccines are commercially available; antimicrobial resistance is increasing; diagnostic and antimicrobial sensitivity testing needs to be improved; and a pen-side test would facilitate more rapid diagnosis and implementation of treatment with antimicrobials. More data on host susceptibility, stress factors, immune response and infectious dose levels are required. The impact of asymptomatic carriers, M. bovis survival in the environment and the role of wildlife in transmitting the disease also needs investigation. To facilitate development of vaccines, further analysis of more M. bovis genomes, its pathogenic mechanisms, including variable surface proteins, is required, along with reproducible disease models.

Development of Mycoplasma pneumoniae biofilms in vitro and the limited role of motility

Mycoplasma pneumoniae is a bacterial pathogen of humans that is a major causative agent of chronic respiratory disease. M. pneumoniae infections often recur even after successful treatment of symptoms with antibiotics, and resistance to antibiotics is increasing worldwide, with nearly complete resistance in some places. Although biofilms often contribute to chronicity and resistance, M. pneumoniae biofilms remain poorly characterized. Scanning electron microscopy revealed that cells of wild-type (WT) M. pneumoniae strain M129 biofilms, as well as mutants II-3 and II-3R, in vitro became increasingly rounded as the biofilm towers matured over 5 days. The role of gliding motility in biofilm formation was addressed by analyzing differences in biofilm architecture in non-motile mutant II-3R and hypermotile mutant prpC-and by using time-lapse microcinematography to measure flux of cells around biofilm towers. There were no major differences in biofilm architecture between WT and motility mutants, with perhaps a slight tendency for the prpC- cells to spread outside towers during early stages of biofilm formation. Consistent with an insignificant role of motility in biofilm development, flux of cells near towers, which was low, was dominated by exit of cells. Immunofluorescence microscopy revealed that motility-associated attachment organelle (AO) proteins exhibited no discernable changes in localization to foci over time, but immunoblotting identified a decrease in steady-state levels of protein P200, which is required for normal gliding speed, as the WT culture aged. Non-adherent strain II-3 and non-motile strain II-3R also exhibited a steady decrease in P200 steady-state levels, suggesting that the decrease in P200 levels was not a response to changes in gliding behavior during maturation. We conclude that M. pneumoniae cells undergo morphological changes as biofilms mature, motility plays no major role in biofilm development, and P200 loss might be related to maturation of cells. This study helps to characterize potential therapeutic targets for M. pneumoniae infections.

Modelling persistent Mycoplasma pneumoniae infection of human airway epithelium

Mycoplasma pneumoniae is a human respiratory tract pathogen causing acute and chronic airway disease states that can include long-term carriage and extrapulmonary spread. The mechanisms of persistence and migration beyond the conducting airways, however, remain poorly understood. We previously described an acute exposure model using normal human bronchial epithelium (NHBE) in air-liquid interface culture, showing that M. pneumoniae gliding motility is essential for initial colonisation and subsequent spread, including localisation to epithelial cell junctions. We extended those observations here, characterizing M. pneumoniae infection of NHBE for up to 4 weeks. Colonisation of the apical surface was followed by pericellular invasion of the basolateral compartment and migration across the underlying transwell membrane. Despite fluctuations in transepithelial electrical resistance and increased NHBE cell desquamation, barrier function remained largely intact. Desquamation was accompanied by epithelial remodelling that included cytoskeletal reorganisation and development of deep furrows in the epithelium. Finally, M. pneumoniae strains S1 and M129 differed with respect to invasion and histopathology, consistent with contrasting virulence in experimentally infected mice. In summary, this study reports pericellular invasion, NHBE cytoskeletal reorganisation, and tissue remodelling with persistent infection in a human airway epithelium model, providing clear insight into the likely route for extrapulmonary spread.

Elongation factor Tu is a multifunctional and processed moonlighting protein

Many bacterial moonlighting proteins were originally described in medically, agriculturally, and commercially important members of the low G + C Firmicutes. We show Elongation factor Tu (Ef-Tu) moonlights on the surface of the human pathogens Staphylococcus aureus (Sa_Ef-Tu) and Mycoplasma pneumoniae (Mpn_Ef-Tu), and the porcine pathogen Mycoplasma hyopneumoniae (Mhp_Ef-Tu). Ef-Tu is also a target of multiple processing events on the cell surface and these were characterised using an N-terminomics pipeline. Recombinant Mpn_Ef-Tu bound strongly to a diverse range of host molecules, and when bound to plasminogen, was able to convert plasminogen to plasmin in the presence of plasminogen activators. Fragments of Ef-Tu retain binding capabilities to host proteins. Bioinformatics and structural modelling studies indicate that the accumulation of positively charged amino acids in short linear motifs (SLiMs), and protein processing promote multifunctional behaviour. Codon bias engendered by an A + T rich genome may influence how positively-charged residues accumulate in SLiMs.

Mycoplasma pneumoniae from the Respiratory Tract and Beyond

Mycoplasma pneumoniae is an important cause of respiratory tract infections in children as well as adults that can range in severity from mild to life-threatening. Over the past several years there has been much new information published concerning infections caused by this organism. New molecular-based tests for M. pneumoniae detection are now commercially available in the United States, and advances in molecular typing systems have enhanced understanding of the epidemiology of infections. More strains have had their entire genome sequences published, providing additional insights into pathogenic mechanisms. Clinically significant acquired macrolide resistance has emerged worldwide and is now complicating treatment. In vitro susceptibility testing methods have been standardized, and several new drugs that may be effective against this organism are undergoing development. This review focuses on the many new developments that have occurred over the past several years that enhance our understanding of this microbe, which is among the smallest bacterial pathogens but one of great clinical importance.

Comprehensive bioinformatics analysis of Mycoplasma pneumoniae genomes to investigate underlying population structure and type-specific determinants

Mycoplasma pneumoniae is a significant cause of respiratory illness worldwide. Despite a minimal and highly conserved genome, genetic diversity within the species may impact disease. We performed whole genome sequencing (WGS) analysis of 107 M. pneumoniae isolates, including 67 newly sequenced using the Pacific BioSciences RS II and/or Illumina MiSeq sequencing platforms. Comparative genomic analysis of 107 genomes revealed >3,000 single nucleotide polymorphisms (SNPs) in total, including 520 type-specific SNPs. Population structure analysis supported the existence of six distinct subgroups, three within each type. We developed a predictive model to classify an isolate based on whole genome SNPs called against the reference genome into the identified subtypes, obviating the need for genome assembly. This study is the most comprehensive WGS analysis for M. pneumoniae to date, underscoring the power of combining complementary sequencing technologies to overcome difficult-to-sequence regions and highlighting potential differential genomic signatures in M. pneumoniae.

Comparison of Mycoplasma pneumoniae Genome Sequences from Strains Isolated from Symptomatic and Asymptomatic Patients

Mycoplasma pneumoniae is a common cause of respiratory tract infections (RTIs) in children. We recently demonstrated that this bacterium can be carried asymptomatically in the respiratory tract of children. To identify potential genetic differences between M. pneumoniae strains that are carried asymptomatically and those that cause symptomatic infections, we performed whole-genome sequence analysis of 20 M. pneumoniae strains. The analyzed strains included 3 reference strains, 3 strains isolated from asymptomatic children, 13 strains isolated from clinically well-defined patients suffering from an upper (n = 4) or lower (n = 9) RTI, and one strain isolated from a follow-up patient who recently recovered from an RTI. The obtained sequences were each compared to the sequences of the reference strains. To find differences between strains isolated from asymptomatic and symptomatic individuals, a variant comparison was performed between the different groups of strains. Irrespective of the group (asymptomatic vs. symptomatic) from which the strains originated, subtype 1 and subtype 2 strains formed separate clusters. We could not identify a specific genotype associated with M. pneumoniae virulence. However, we found marked genetic differences between clinical isolates and the reference strains, which indicated that the latter strains may not be regarded as appropriate representatives of circulating M. pneumoniae strains.

Epidemiology of Mycoplasma pneumoniae Infections in Japan and Therapeutic Strategies for Macrolide-Resistant M. pneumoniae

Pneumonia caused by Mycoplasma pneumoniae (M. pneumoniae pneumonia) is a major cause of community-acquired pneumonia worldwide. The surveillance of M. pneumoniae pneumonia is important for etiological and epidemiological studies of acute respiratory infections. In Japan, nation-wide surveillance of M. pneumoniae pneumonia has been conducted as a part of the National Epidemiological Surveillance of Infectious Diseases (NESID) program. This surveillance started in 1981, and significant increases in the numbers of M. pneumoniae pneumonia patients were noted in 1984, 1988, 2006, 2010, 2011, 2012, and 2015. The epidemics in 2011 and 2012 were particularly widespread and motivated researchers to conduct detailed epidemiological studies, including genotyping and drug resistance analyses of M. pneumoniae isolates. The genotyping studies based on the p1 gene sequence suggested that the p1 gene type 1 lineage has been dominant in Japan since 2003, including the epidemic period during 2011-2012. However, more detailed p1 typing analysis is required to determine whether the type 2 lineages become more relevant after the dominance of the type 1 lineage. There has been extensive research interest in implications of the p1 gene types on the epidemiology of M. pneumoniae infections. Serological characterizations of sera from patients have provided a glimpse into these associations, showing the presence of type specific antibody in the patient sera. Another important epidemiological issue of M. pneumoniae pneumonia is the emergence of macrolide-resistant M. pneumoniae (MRMP). MRMPs were noted among clinical isolates in Japan after 2000. At present, the isolation rate of MRMPs from pediatric patients is estimated at 50-90% in Japan, depending on the specific location. In view of the situation, Japanese societies have issued guiding principles for treating M. pneumoniae pneumonia. In these guiding principles, macrolides are still recommended as the first-line drug, however, if the fever does not subside in 48-72 h from first-line drug administration, a change of antibiotics to second-line drugs is recommended.

Mycoplasma agalactiae Secretion of β-(1→6)-Glucan, a Rare Polysaccharide in Prokaryotes, Is Governed by High-Frequency Phase Variation

Mycoplasmas are minimal, wall-less bacteria but have retained the ability to secrete complex carbohydrate polymers that constitute a glycocalyx. In members of the Mycoplasma mycoides cluster, which are important ruminant pathogens, the glycocalyx includes both cell-attached and cell-free polysaccharides. This report explores the potential secretion of polysaccharides by M. agalactiae, another ruminant pathogen that belongs to a distant phylogenetic group. Comparative genomic analyses showed that M. agalactiae possesses all the genes required for polysaccharide secretion. Notably, a putative synthase gene (gsmA) was identified, by in silico reconstruction of the biosynthetic pathway, that could be involved in both polymerization and export of the carbohydrate polymers. M. agalactiae polysaccharides were then purified in vitro and found to be mainly cell attached, with a linear β-(1→6)-glucopyranose structure [β-(1→6)-glucan]. Secretion of β-(1→6)-glucan was further shown to rely on the presence of a functional gsmA gene, whose expression is subjected to high-frequency phase variation. This event is governed by the spontaneous intraclonal variation in length of a poly(G) tract located in the gsmA coding sequence and was shown to occur in most of the M. agalactiae clinical isolates tested in this study. M. agalactiae susceptibility to serum-killing activity appeared to be dictated by ON/OFF switching of β-(1→6)-glucan secretion, suggesting a role of this phenomenon in survival of the pathogen when it invades the host bloodstream. Finally, β-(1→6)-glucan secretion was not restricted to M. agalactiae but was detected also in M. mycoides subsp. capri PG3(T), another pathogen of small ruminants.

IMPORTANCE

Many if not all bacteria are able to secrete polysaccharides, either attached to the cell surface or exported unbound into the extracellular environment. Both types of polysaccharides can play a role in bacterium-host interactions. Mycoplasmas are no exception despite their poor overall metabolic capacity. We showed here that M. agalactiae secretes a capsular β-(1→6)-glucopyranose thanks to a specific glycosyltransferase with synthase activity. This secretion is governed by high-frequency ON/OFF phase variation that might be crucial in mycoplasma host dissemination, as cell-attached β-(1→6)-glucopyranose increases serum-killing susceptibility. Our results provide functional genetic data about mycoplasmal glycosyltransferases with dual functions, i.e., assembly and export of the sugar polymers across the cell membrane. Furthermore, we demonstrated that nonprotein epitopes can be subjected to surface antigenic variation in mycoplasmas. Finally, the present report contributes to unravel the role of secreted polysaccharides in the virulence and pathogenicity of these peculiar bacteria.

Potential Molecular Targets for Narrow-Spectrum Agents to Combat Mycoplasma pneumoniae Infection and Disease

As Mycoplasma pneumoniae macrolide resistance grows and spreads worldwide, it is becoming more important to develop new drugs to prevent infection or limit disease. Because other mycoplasma species have acquired resistance to other classes of antibiotics, it is reasonable to presume that M. pneumoniae can do the same, so switching to commonly used antibiotics like fluoroquinolones will not result in forms of therapy with long-term utility. Moreover, broad-spectrum antibiotics can have serious consequences for the patient, as these drugs may have severe impacts on the natural microbiota of the individual, compromising the health of the patient either short-term or long-term. Therefore, developing narrow-spectrum antibiotics that effectively target only M. pneumoniae and no more than a small portion of the microbiota is likely to yield impactful, positive results that can be used perhaps indefinitely to combat M. pneumoniae. Development of these agents requires a deep understanding of the basic biology of M. pneumoniae, in many areas deeper than what is currently known. In this review, we discuss potential targets for new, narrow-spectrum agents and both the positive and negative aspects of selecting these targets, which include toxic molecules, metabolic pathways, and attachment and motility. By gathering this information together, we anticipate that it will be easier for researchers to evaluate topics of priority for study of M. pneumoniae.

Antibody Response to Mycoplasma pneumoniae: Protection of Host and Influence on Outbreaks?

In humans of all ages, the cell wall-less and genome-reduced species Mycoplasma pneumoniae can cause infections of the upper and lower respiratory tract. The well-documented occurrence of major peaks in the incidence of community-acquired pneumonia cases reported world-wide, the multifaceted clinical manifestations of infection and the increasing number of resistant strains provide reasons for ongoing interest in the pathogenesis of mycoplasmal disease. The results of recent studies have provided insights into the interaction of the limited virulence factors of the bacterium with its host. In addition, the availability of complete M. pneumoniae genomes from patient isolates and the development of proteomic methods for investigation of mycoplasmas have not only allowed characterization of sequence divergences between strains but have also shown the importance of proteins and protein parts for induction of the immune reaction after infection. This review focuses on selected aspects of the humoral host immune response as a factor that might influence the clinical course of infections, subsequent protection in cases of re-infections and changes of epidemiological pattern of infections. The characterization of antibodies directed to defined antigens and approaches to promote their induction in the respiratory mucosa are also preconditions for the development of a vaccine to protect risk populations from severe disease due to M. pneumoniae.

General N-and O-Linked Glycosylation of Lipoproteins in Mycoplasmas and Role of Exogenous Oligosaccharide

The lack of a cell wall, flagella, fimbria, and other extracellular appendages and the possession of only a single membrane render the mycoplasmas structurally simplistic and ideal model organisms for the study of glycoconjugates. Most species have genomes of about 800 kb and code for few proteins predicted to have a role in glycobiology. The murine pathogens Mycoplasma arthritidis and Mycoplasma pulmonis have only a single gene annotated as coding for a glycosyltransferase but synthesize glycolipid, polysaccharide and glycoproteins. Previously, it was shown that M. arthritidis glycosylated surface lipoproteins through O-linkage. In the current study, O-linked glycoproteins were similarly found in M. pulmonis and both species of mycoplasma were found to also possess N-linked glycans at residues of asparagine and glutamine. Protein glycosylation occurred at numerous sites on surface-exposed lipoproteins with no apparent amino acid sequence specificity. The lipoproteins of Mycoplasma pneumoniae also are glycosylated. Glycosylation was dependent on the glycosidic linkages from host oligosaccharides. As far as we are aware, N-linked glycoproteins have not been previously described in Gram-positive bacteria, the organisms to which the mycoplasmas are phylogenetically related. The findings indicate that the mycoplasma cell surface is heavily glycosylated with implications for the modulation of mycoplasma-host interactions.

Comparative "-omics" in Mycoplasma pneumoniae Clinical Isolates Reveals Key Virulence Factors

The human respiratory tract pathogen M. pneumoniae is one of the best characterized minimal bacterium. Until now, two main groups of clinical isolates of this bacterium have been described (types 1 and 2), differing in the sequence of the P1 adhesin gene. Here, we have sequenced the genomes of 23 clinical isolates of M. pneumoniae. Studying SNPs, non-synonymous mutations, indels and genome rearrangements of these 23 strains and 4 previously sequenced ones, has revealed new subclasses in the two main groups, some of them being associated with the country of isolation. Integrative analysis of in vitro gene essentiality and mutation rates enabled the identification of several putative virulence factors and antigenic proteins; revealing recombination machinery, glycerol metabolism and peroxide production as possible factors in the genetics and physiology of these pathogenic strains. Additionally, the transcriptomes and proteomes of two representative strains, one from each of the two main groups, have been characterized to evaluate the impact of mutations on RNA and proteins levels. This study has revealed that type 2 strains show higher expression levels of CARDS toxin, a protein recently shown to be one of the major factors of inflammation. Thus, we propose that type 2 strains could be more toxigenic than type 1 strains of M. pneumoniae.