Identification of fibronectin-binding proteins in Mycoplasma gallisepticum strain R

Immune Evasion of Mycoplasma gallisepticum: An Overview

Mycoplasma gallisepticum is one of the smallest self-replicating organisms. It causes chronic respiratory disease, leading to significant economic losses in poultry industry. Following M. gallisepticum invasion, the pathogen can persist in the host owing to its immune evasion, resulting in long-term chronic infection. The strategies of immune evasion by mycoplasmas are very complex and recent research has unraveled these sophisticated mechanisms. The antigens of M. gallisepticum exhibit high-frequency changes in size and expression cycle, allowing them to evade the activation of the host humoral immune response. M. gallisepticum can invade non-phagocytic chicken cells and also regulate microRNAs to modulate cell proliferation, inflammation, and apoptosis in tracheal epithelial cells during the disease process. M. gallisepticum has been shown to transiently activate the inflammatory response and then inhibit it by suppressing key inflammatory mediators, avoiding being cleared. The regulation and activation of immune cells are important for host response against mycoplasma infection. However, M. gallisepticum has been shown to interfere with the functions of macrophages and lymphocytes, compromising their defense capabilities. In addition, the pathogen can cause immunological damage to organs by inducing an inflammatory response, cell apoptosis, and oxidative stress, leading to immunosuppression in the host. This review comprehensively summarizes these evasion tactics employed by M. gallisepticum, providing valuable insights into better prevention and control of mycoplasma infection.

Mycoplasma synoviae LP78 is a fibronectin/plasminogen binding protein, putative adhesion, and potential diagnostic antigen

Mycoplasma synoviae (M. synoviae) is one of the major poultry pathogens causing infectious synovitis, airsacculitis, a high incidence of shell breakage, and egg production loss. However, the pathogenesis of M. synoviae remains unclear. Adhesion of mycoplasmas to host cells is a crucial step in infection and colonization. The purpose of this study was to determine the adhesive function of a putative P80 family lipoprotein (LP78) and evaluate its application in the detection of antibodies against M. synoviae. Recombinant LP78 (rLP78) was expressed in the supernatant component of Escherichia coli and mouse anti-rLP78 serum was prepared. Bioinformatic analysis and western blotting results revealed that LP78 was conservative among M. synoviae strains. It was distributed not only in the cytoplasm but also on the membrane of M. synoviae through western blotting and indirect immunofluorescence (IFA). The adherence of M. synoviae to DF-1 cells was significantly inhibited by mouse anti-rLP78 serum (p < 0.01). IFA revealed that rLP78 adhered to DF-1 cells, and this adherence was prevented by mouse anti-rLP78 serum. Furthermore, rLP78 was found to bind to the DF-1 cells membrane proteins in a dose-dependent manner by enzyme-linked immunosorbent assay (ELISA). Screening of DF-1 cells membrane proteins by western blotting showed that proteins with molecular weight of 35-40 kDa and 55-70 kDa bound to rLP78. Moreover, rLP78 was identified to be a fibronectin/plasminogen binding protein. The sensitivity and specificity of rLP78-based iELISA were 85.7 and 94.1%, respectively. The maximum dilution of positive serum (HI titer, 1:128) detected via rLP78-based iELISA was 1:6,400, whereas that detected using a commercial ELISA kit was 1:12,800-1:25,600. Both rLP78-based iELISA and the commercial ELISA kit detected seroconversion after 7 days of challenge and immunization. No cross-reactivity with positive sera against other avian pathogens was observed in rLP78-based iELISA. Collectively, these results indicate that LP78 is a fibronectin/plasminogen-binding adhesion protein of M. synoviae and a potential diagnostic antigen. The present study will facilitate a better understanding of the pathogenesis of M. synoviae and the development of new diagnostic.

Infection, Transmission, Pathogenesis and Vaccine Development against Mycoplasma gallisepticum

Mycoplasma sp. comprises cell wall-less bacteria with reduced genome size and can infect mammals, reptiles, birds, and plants. Avian mycoplasmosis, particularly in chickens, is primarily caused by Mycoplasma gallisepticum (MG) and Mycoplasma synoviae. It causes infection and pathology mainly in the respiratory, reproductive, and musculoskeletal systems. MG is the most widely distributed pathogenic avian mycoplasma with a wide range of host susceptibility and virulence. MG is transmitted both by horizontal and vertical routes. MG infection induces innate, cellular, mucosal, and adaptive immune responses in the host. Macrophages aid in phagocytosis and clearance, and B and T cells play critical roles in the clearance and prevention of MG. The virulent factors of MG are adhesion proteins, lipoproteins, heat shock proteins, and antigenic variation proteins, all of which play pivotal roles in host cell entry and pathogenesis. Prevention of MG relies on farm and flock biosecurity, management strategies, early diagnosis, use of antimicrobials, and vaccination. This review summarizes the vital pathogenic mechanisms underlying MG infection and recapitulates the virulence factors of MG-host cell adhesion, antigenic variation, nutrient transport, and immune evasion. The review also highlights the limitations of current vaccines and the development of innovative future vaccines against MG.

Novel mycoplasma nucleomodulin MbovP475 decreased cell viability by regulating expression of CRYAB and MCF2L2

Nucleomodulins are secreted bacterial proteins whose molecular targets are located in host cell nuclei. They are gaining attention as critical virulence factors that either modify the epigenetics of host cells or directly regulate host gene expression. Mycoplasma bovis is a major veterinary pathogen that secretes several potential virulence factors. The aim of this study was to determine whether any of their secreted proteins might function as nucleomodulins. After an initial in silico screening, the nuclear localization of the secreted putative lipoprotein MbovP475 of M. bovis was demonstrated in bovine macrophage cell line (BoMac) experimentally infected with M. bovis. Through combined application of ChIP-seq, Electrophoretic mobility shift assay (EMSA) and surface plasmon resonance (SPR) analysis, MbovP475 was determined to bind the promoter regions of the cell cycle central regulatory genes CRYAB and MCF2L2. MbovP475 has similar secondary structures with the transcription activator-like effectors (TALEs). Screening of various mutants affecting the potential DNA binding sites indicated that the residues ²⁴²NI²⁴³ within MbovP475 loop region of the helix-loop-helix domain were essential to its DNA binding activity, thereby contributing to decrease in BoMac cell viability. In conclusion, this is the first report to confirm M. bovis secretes a conserved TALE-like nucleomodulin that binds the promoters of CRYAB and MCF2L2 genes, and subsequently down-regulates their expression and decreases BoMac cell viability. Therefore, this study offers a new understanding of mycoplasma pathogenesis.

Long COVID and the Neuroendocrinology of Microbial Translocation Outside the GI Tract: Some Treatment Strategies

Similar to previous pandemics, COVID-19 has been succeeded by well-documented post-infectious sequelae, including chronic fatigue, cough, shortness of breath, myalgia, and concentration difficulties, which may last 5 to 12 weeks or longer after the acute phase of illness. Both the psychological stress of SARS-CoV-2 infection and being diagnosed with COVID-19 can upregulate cortisol, a stress hormone that disrupts the efferocytosis effectors, macrophages, and natural killer cells, leading to the excessive accumulation of senescent cells and disruption of biological barriers. This has been well-established in cancer patients who often experience unrelenting fatigue as well as gut and blood–brain barrier dysfunction upon treatment with senescence-inducing radiation or chemotherapy. In our previous research from 2020 and 2021, we linked COVID-19 to myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) via angiotensin II upregulation, premature endothelial senescence, intestinal barrier dysfunction, and microbial translocation from the gastrointestinal tract into the systemic circulation. In 2021 and 2022, these hypotheses were validated and SARS-CoV-2-induced cellular senescence as well as microbial translocation were documented in both acute SARS-CoV-2 infection, long COVID, and ME/CFS, connecting intestinal barrier dysfunction to disabling fatigue and specific infectious events. The purpose of this narrative review is to summarize what is currently known about host immune responses to translocated gut microbes and how these responses relate to fatiguing illnesses, including long COVID. To accomplish this goal, we examine the role of intestinal and blood–brain barriers in long COVID and other illnesses typified by chronic fatigue, with a special emphasis on commensal microbes functioning as viral reservoirs. Furthermore, we discuss the role of SARS-CoV-2/Mycoplasma coinfection in dysfunctional efferocytosis, emphasizing some potential novel treatment strategies, including the use of senotherapeutic drugs, HMGB1 inhibitors, Toll-like receptor 4 (TLR4) blockers, and membrane lipid replacement.

The expression of GapA and CrmA correlates with the Mycoplasma gallisepticum in vitro infection process in chicken TOCs

Mycoplasma (M.) gallisepticum is the most pathogenic mycoplasma species in poultry. Infections cause mild to severe clinical symptoms associated with respiratory epithelial lesion development. Adherence, biofilm formation, and cell invasion of M. gallisepticum contribute to successful infection, immune evasion, and survival within the host. The important M. gallisepticum membrane-bound proteins, GapA and CrmA, are key factors for host cell interaction and the bacterial life-cycle, including its gliding motility, although their precise role in the individual infection step is not yet fully understood. In this study, we investigated the correlation between the host-pathogen interaction and the GapA/CrmA expression in an environment that represents the natural host's multicellular compartment. We used an in vitro tracheal organ culture (TOC) model, allowing the investigation of the M. gallisepticum variants, Rlow, RCL1, RCL2, and Rhigh, under standardised conditions. In this regard, we examined the bacterial adherence, motility and colonisation pattern, host lesion development and alterations of mucociliary clearance. Compared to low virulent RCL2 and Rhigh, the high virulent Rlow and RCL1 were more efficient in adhering to TOCs and epithelium colonisation, including faster movement from the cilia tips to the apical membrane and subsequent cell invasion. RCL2 and Rhigh showed a more localised invasion pattern, accompanied by significantly fewer lesions than Rlow and RCL1. Unrelated to virulence, comparable mucus production was observed in all M. gallisepticum infected TOCs. Overall, the present study demonstrates the role of GapA/CrmA in virulence factors from adherence to colonisation, as well as the onset and severity of lesion development in the tracheal epithelium.

Beware of Mycoplasma Anti-immunoglobulin Strategies

Mycoplasmas are small, genome-reduced bacteria. They are obligate parasites that can be found in a wide range of host species, including the majority of livestock animals and humans. Colonization of the host can result in a wide spectrum of outcomes. In many cases, these successful parasites are considered commensal, as they are found in the microbiota of asymptomatic carriers. Conversely, mycoplasmas can also be pathogenic, as they are associated with a range of both acute and chronic inflammatory diseases which are problematic in veterinary and human medicine. The chronicity of mycoplasma infections and the ability of these bacteria to infect even recently vaccinated individuals clearly indicate that they are able to successfully evade their host’s humoral immune response. Over the years, multiple strategies of immune evasion have been identified in mycoplasmas, with a number of them aimed at generating important antigenic diversity. More recently, mycoplasma-specific anti-immunoglobulin strategies have also been characterized. Through the expression of the immunoglobulin-binding proteins protein M or mycoplasma immunoglobulin binding (MIB), mycoplasmas have the ability to target the host’s antibodies and to prevent them from interacting with their cognate antigens. In this review, we discuss how these discoveries shed new light on the relationship between mycoplasmas and their host’s immune system. We also propose that these strategies should be taken into consideration for future studies, as they are key to our understanding of mycoplasma diseases' chronic and inflammatory nature and are probably a contributing factor to reduce vaccine efficacy.

A Computational Reverse Vaccinology Approach for the Design and Development of Multi-Epitopic Vaccine Against Avian Pathogen Mycoplasma gallisepticum

Avian mycoplasma is a bacterial disease causing chronic respiratory disease (CRD) in poultry industries with high economic losses. The eradication of this disease still remains as a challenge. A multi-epitope prophylactic vaccine aiming the antigenic proteins of Mycoplasma gallisepticum can be a capable candidate to eradicate this infection. The present study is focused to design a multi-epitope vaccine candidate consisting of cytotoxic T-cell (CTL), helper T-cell (HTL), and B-cell epitopes of antigenic proteins, using immunoinformatics strategies. The multi-epitopic vaccine was designed, and its tertiary model was predcited, which was further refined and validated by computational tools. After initial validation, molecular docking was performed between multi-epitope vaccine construct and chicken TLR-2 and 5 receptors, which predicted effective binding. The in silico results specify the structural stability, precise specificity, and immunogenic response of the designed multi-epitope vaccine, and it could be an appropriate vaccine candidate for the M. gallisepticum infection.

Multi-epitope-Based Vaccine Designed by Targeting Cytoadherence Proteins of Mycoplasma gallisepticum

Mycoplasma gallisepticum causes chronic respiratory disease in chickens leading to large economic losses in the poultry industry, and the impacts remain to be a great challenge for a longer period. Among the other approaches, a vaccine targeting the adhesion proteins of M. gallisepticum would be a promising candidate in controlling the infection. Thus, the present study is aimed to design a multi-epitope vaccine candidate using cytoadhesion proteins of M. gallisepticum through an advanced immunoinformatics approach. As a result, the multi-epitope vaccine was constructed, which comprised potential T-cell and B-cell binding epitopes with appropriate adjuvants. The designed multi-epitope vaccine represented high antigenicity with viable physiochemical properties. The prospective three-dimensional structure of the epitope was predicted, refined, and validated. The molecular docking analysis of multi-epitope vaccine candidates with the chicken Toll-like receptor-5 predicted effective binding. Furthermore, codon optimization and in silico cloning ensured high expression. Thus, the present finding indicates that the engineered multi-epitope vaccine is structurally stable and can induce a strong immune response. Furthermore, the multi-epitope vaccine is suggested to be a suitable vaccine candidate for the M. gallisepticum infection due to its effective binding capacity and precise specificity.

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.

Mycoplasma bovis mbfN Encodes a Novel LRR Lipoprotein That Undergoes Proteolytic Processing and Binds Host Extracellular Matrix Components

Mycoplasma bovis causes serious infections in ruminants, leading to huge economic losses. Lipoproteins are key components of the mycoplasma membrane and are believed to function in nutrient acquisition, adherence, enzymatic interactions with the host, and induction of the host's immune response to infection. Many genes of M. bovis have not been assigned functions, in part because of their low sequence similarity with other bacteria, making it difficult to extrapolate gene functions. This study examined functions of a surface-localized leucine-rich repeat (LRR) lipoprotein encoded by mbfN of M. bovis PG45. Homologs of MbfN were detected as 48-kDa peptides by Western blotting in all the strains of M. bovis included in this study, with the predicted 70-kDa full-length polypeptide detected in some strains. Sequence analysis of the gene revealed the absence in some strains of a region encoding the carboxyl-terminal 147 amino acids found in strain PG45, which could account for the variation detected by immunoblotting. In silico analysis of MbfN suggested that it may have an adhesion-related function. In vitro binding assays confirmed MbfN to be a fibronectin and heparin-binding protein. Disruption of mbfN in M. bovis PG45 significantly reduced (P = 0.033) the adherence of M. bovis PG45 to MDBK cells in vitro, demonstrating the role of MbfN as an adhesin.IMPORTANCE Experimental validation of the putative functions of genes in M. bovis will advance our understanding of the basic biology of this economically important pathogen and is crucial in developing prevention strategies. This study demonstrated the extracellular matrix binding ability of a novel immunogenic lipoprotein of M. bovis, and the role of this protein in adhesion by M. bovis suggests that it could play a role in virulence.

Rasheed M, Chen Y, Hu C, Chen H, Sagné E, Citti C, Guo A. An emerging role for cyclic dinucleotide phosphodiesterase and nanoRNase activities in Mycoplasma bovis: Securing survival in cell culture

Mycoplasmas are host-restricted prokaryotes with a nearly minimal genome. To overcome their metabolic limitations, these wall-less bacteria establish intimate interactions with epithelial cells at mucosal surfaces. The alarming rate of antimicrobial resistance among pathogenic species is of particular concern in the medical and veterinary fields. Taking advantage of the reduced mycoplasma genome, random transposon mutagenesis was combined with high-throughput screening in order to identify key determinants of mycoplasma survival in the host-cell environment and potential targets for drug development. With the use of the ruminant pathogen Mycoplasma bovis as a model, three phosphodiesterases of the DHH superfamily were identified as essential for the proliferation of this species under cell culture conditions, while dispensable for axenic growth. Despite a similar domain architecture, recombinant Mbov_0327 and Mbov_0328 products displayed different substrate specificities. While rMbovP328 protein exhibited activity towards cyclic dinucleotides and nanoRNAs, rMbovP327 protein was only able to degrade nanoRNAs. The Mbov_0276 product was identified as a member of the membrane-associated GdpP family of phosphodiesterases that was found to participate in cyclic dinucleotide and nanoRNA degradation, an activity which might therefore be redundant in the genome-reduced M. bovis. Remarkably, all these enzymes were able to convert their substrates into mononucleotides, and medium supplementation with nucleoside monophosphates or nucleosides fully restored the capacity of a Mbov_0328/0327 knock-out mutant to grow under cell culture conditions. Since mycoplasmas are unable to synthesize DNA/RNA precursors de novo, cyclic dinucleotide and nanoRNA degradation are likely contributing to the survival of M. bovis by securing the recycling of purines and pyrimidines. These results point toward proteins of the DHH superfamily as promising targets for the development of new antimicrobials against multidrug-resistant pathogenic mycoplasma species.

Multiple differences in pathogen-host cell interactions following a bacterial host shift

Novel disease emergence is often associated with changes in pathogen traits that enable pathogen colonisation, persistence and transmission in the novel host environment. While understanding the mechanisms underlying disease emergence is likely to have critical implications for preventing infectious outbreaks, such knowledge is often based on studies of viral pathogens, despite the fact that bacterial pathogens may exhibit very different life histories. Here, we investigate the ability of epizootic outbreak strains of the bacterial pathogen, Mycoplasma gallisepticum, which jumped from poultry into North American house finches (Haemorhous mexicanus), to interact with model avian cells. We found that house finch epizootic outbreak strains of M. gallisepticum displayed a greater ability to adhere to, invade, persist within and exit from cultured chicken embryonic fibroblasts, than the reference virulent (R_low) and attenuated (R_high) poultry strains. Furthermore, unlike the poultry strains, the house finch epizootic outbreak strain HF_1994 displayed a striking lack of cytotoxicity, even exerting a cytoprotective effect on avian cells. Our results suggest that, at epizootic outbreak in house finches, M. gallisepticum was particularly adept at using the intra-cellular environment, which may have facilitated colonisation, dissemination and immune evasion within the novel finch host. Whether this high-invasion phenotype is similarly displayed in interactions with house finch cells, and whether it contributed to the success of the host shift, remains to be determined.

Mbov_0503 Encodes a Novel Cytoadhesin that Facilitates Mycoplasma bovis Interaction with Tight Junctions

Molecules contributing to microbial cytoadhesion are important virulence factors. In Mycoplasma bovis, a minimal bacterium but an important cattle pathogen, binding to host cells is emerging as a complex process involving a broad range of surface-exposed structures. Here, a new cytoadhesin of M. bovis was identified by producing a collection of individual knock-out mutants and evaluating their binding to embryonic bovine lung cells. The cytoadhesive-properties of this surface-exposed protein, which is encoded by Mbov_0503 in strain HB0801, were demonstrated at both the mycoplasma cell and protein levels using confocal microscopy and ELISA. Although Mbov_0503 disruption was only associated in M. bovis with a partial reduction of its binding capacity, this moderate effect was sufficient to affect M. bovis interaction with the host-cell tight junctions, and to reduce the translocation of this mycoplasma across epithelial cell monolayers. Besides demonstrating the capacity of M. bovis to disrupt tight junctions, these results identified novel properties associated with cytoadhesin that might contribute to virulence and host colonization. These findings provide new insights into the complex interplay taking place between wall-less mycoplasmas and the host-cell surface.

Development of Molecular Methods for Rapid Differentiation of Mycoplasma gallisepticum Vaccine Strains from Field Isolates

Mycoplasma gallisepticum is among the most economically significant mycoplasmas causing production losses in poultry. Seven melt-curve and agarose gel-based mismatch amplification mutation assays (MAMAs) and one PCR are provided in the present study to distinguish the M. gallisepticum vaccine strains and field isolates based on mutations in the crmA, gapA, lpd, plpA, potC, glpK, and hlp2 genes. A total of 239 samples (M. gallisepticum vaccine and type strains, pure cultures, and clinical samples) originating from 16 countries and from at least eight avian species were submitted to the presented assays for validation or in blind tests. A comparison of the data from 126 samples (including sequences available at GenBank) examined by the developed assays and a recently developed multilocus sequence typing assay showed congruent typing results. The sensitivity of the melt-MAMA assays varied between 10¹ and 10⁴ M. gallisepticum template copies/reaction, while that of the agarose-MAMAs ranged from 10³ to 10⁵ template copies/reaction, and no cross-reactions occurred with other Mycoplasma species colonizing birds. The presented assays are also suitable for discriminating multiple strains in a single sample. The developed assays enable the differentiation of live vaccine strains by targeting two or three markers/vaccine strain; however, considering the high variability of the species, the combined use of all assays is recommended. The suggested combination provides a reliable tool for routine diagnostics due to the sensitivity and specificity of the assays, and they can be performed directly on clinical samples and in laboratories with basic PCR equipment.

Variable Lipoprotein Hemagglutinin A Gene (vlhA) Expression in Variant Mycoplasma gallisepticum Strains In Vivo

Mycoplasma gallisepticum, the primary etiologic agent of chronic respiratory disease, is a significant poultry pathogen, causing severe inflammation and leading to economic losses worldwide. Immunodominant proteins encoded by the variable lipoprotein and hemagglutinin (vlhA) gene family are thought to be important for M. gallisepticum-host interaction, pathogenesis, and immune evasion, but their exact role remains unknown. Previous work has demonstrated that vlhA phase variation is dynamic throughout the earliest stages of infection, with vlhA 3.03 being the predominant vlhA expressed during the initial infection, and that the pattern of dominant vlhA expression may be nonrandom and regulated by previously unrecognized mechanisms. To further investigate this gene family, we assessed the vlhA profile of two well-characterized vaccine strains, GT5 and Mg7, a vlhA 3.03 mutant strain, and an M. gallisepticum population expressing an alternative immunodominant vlhA Here, we report that two M. gallisepticum vaccine strains show different vlhA profiles over the first 2 days of infection compared to that of wild-type R_low, while the population expressing an alternative immunodominant vlhA gene reverted to a profile indistinguishable from that of wild-type R_low Additionally, we observed a slight shift in the vlhA gene expression profile but no reduction in virulence in a vlhA 3.03 mutant. Taken together, these data further support the hypothesis that M. gallisepticum vlhA genes change in a nonstochastic temporal progression of expression and that vlhA 3.03, while preferred, is not required for virulence. Collectively, these data may be important in elucidating mechanisms of colonization and overall pathogenesis of M. gallisepticum.

P27 (MBOV_RS03440) is a novel fibronectin binding adhesin of Mycoplasma bovis

Mycoplasma bovis, one of the major pathogens of bovine respiratory disease, binds to respiratory epithelial cells resulting in severe pneumonia and tissue damage. This study was designed to identify the adhesive function of a putative 27-kDa M. bovis lipoprotein, encoded by the gene MBOV_RS03440 and designated as P27. The gene was cloned and overexpressed to produce antibodies against the recombinant P27 (rP27). The western blot and flow cytometry assay confirmed P27 to be a surface-localized protein, while ELISA confirmed it to be an immunogenic protein. Confocal immunofluorescence microscopy demonstrated that rP27 bound to embryonic bovine lung (EBL) cell monolayers in a dose-dependent manner. Furthermore, anti-rP27 antiserum inhibited the attachment of M. bovis to EBL cells demonstrating the binding specificity of P27 to EBL cells. The attachment of rP27 to EBL cells was mediated by fibronectin (Fn), an extracellular matrix component. The interaction between rP27 and Fn was qualitatively and quantitatively monitored by ligand immunoblot assay, ELISA, and biolayer interferometry. Collectively, these results indicate that P27 is a novel Fn-binding, immunogenic adhesive protein of M. bovis, thereby contributing to the further understanding of the molecular pathogenesis of M. bovis.

TrmFO, a Fibronectin-Binding Adhesin of Mycoplasma bovis

Mycoplasma bovis is an important pathogenic mycoplasma, causing the cattle industry serious economic losses. Adhesion is a crucial step in the mycoplasmas' infection and colonization process; fibronectin (Fn), an extracellular matrix glycoprotein, is a molecular bridge between the bacterial adhesins and host cell receptors. The present study was designed to characterize the Fn-binding ability of methylenetetrahydrofolate-tRNA-(uracil-5-)-methyltransferase (TrmFO) and its role in M. bovis cytoadherence. The trmFO (MBOV_RS00785) gene was cloned and expressed in E. coli BL21, and polyclonal antibodies against the recombinant TrmFO (rTrmFO) were raised in rabbits. Immunoblotting demonstrated that TrmFO was an immunogenic component, and the TrmFO expression was conserved in different M. bovis isolates. The mycoplasmacidal assay further showed that in the presence of complement, rabbit anti-recombinant TrmFO serum exhibited remarkable mycoplasmacidal efficacy. TrmFO was detected in both the M. bovis membrane and cytoplasm. By ligand dot blot and enzyme-linked immunosorbent assay (ELISA) binding assay, we found that rTrmFO bound Fn in a dose-dependent manner. Immunostaining visualized by confocal laser scanning microscopy showed that rTrmFO had capacity to adhere to the embryonic bovine lung (EBL) cells. In addition, the adhesion of M. bovis and rTrmFO to EBL cells could be inhibited by anti-rTrmFO antibodies. To the best of our knowledge, this is the first report to characterize the Fn-binding ability of TrmFO and its role in the bacterial adhesion to host cells.

P19 contributes to Mycoplasma mycoides subsp. mycoides adhesion to EBL cells

Mycoplasma mycoides subsp. mycoides (Mmm) is the causative agent of contagious bovine pleuropneumonia (CBPP). The virulent Mmm Ben-1 strain was isolated from the lung of a CBPP-infected cow in China in the 1950s. To attenuate the virulence of the Ben-1 strain and preserve its protective ability, the isolate was re-isolated after inoculation into the testicles of rabbits and into the rabbit thorax. As a result, after the subsequent isolates were continuously passaged 468 times in rabbits, its pathogenicity to cattle decreased. However, the molecular mechanisms leading to attenuation of the Mmm Ben-1 remain unknown. We compared the entire genomes of the Ben-1 strain and the 468 th generation strain passaged in rabbits (Ben-468) and discovered that a putative protein gene named p19 was absent from the Ben-468 strain. The p19 gene was cloned and expressed in Escherichia coli to obtain recombinant P19 (rP19). Western blot analysis demonstrated that the P19 protein is detected in the cell-membrane fraction, the cell-soluble cytosolic fraction and whole-cell lysate of the Mmm Ben-1 strain. The rP19 can interact with international standard serum against CBPP. Immunostaining visualised via confocal laser scanning microscopy indicated that P19 is able to adhere to embryonic bovine lung (EBL) cells, and this finding was also confirmed by a sandwich ELISA. We also found that anti-rP19 serum could inhibit the adhesion of the Mmm Ben-1 total proteins to EBL cells.

Global Changes in Mycoplasma gallisepticum Phase-Variable Lipoprotein Gene vlhA Expression during In Vivo Infection of the Natural Chicken Host

Mycoplasma gallisepticum is the primary etiologic agent of chronic respiratory disease in poultry, a disease largely affecting the respiratory tract and causing significant economic losses worldwide. Immunodominant proteins encoded by members of the variable lipoprotein and hemagglutinin (vlhA) gene family are thought to be important for mechanisms of M. gallisepticum-host interaction, pathogenesis, and immune evasion, but their exact role and the overall nature of their phase variation are unknown. To better understand these mechanisms, we assessed global transcriptomic vlhA gene expression directly from M. gallisepticum populations present on tracheal mucosae during a 7-day experimental infection in the natural chicken host. Here we report differences in both dominant and minor vlhA gene expression levels throughout the first week of infection and starting as early as day 1 postinfection, consistent with a functional role not dependent on adaptive immunity for driving phase variation. Notably, data indicated that, at given time points, specific vlhA genes were similarly dominant in multiple independent hosts, suggesting a nonstochastic temporal progression of dominant vlhA gene expression in the colonizing bacterial population. The dominant expression of a given vlhA gene was not dependent on the presence of 12-copy GAA trinucleotide repeats in the promoter region and did not revert to the predominate vlhA gene when no longer faced with host pressures. Overall, these data indicate that vlhA phase variation is dynamic throughout the earliest stages of infection and that the pattern of dominant vlhA expression may be nonrandom and regulated by previously unrecognized mechanisms.

Characterization of triosephosphate isomerase from Mycoplasma gallisepticum

Triosephosphate isomerase (Tpi) is a glycolytic enzyme that is essential for efficient energy production in many pathogens. However, its function in Mycoplasma gallisepticum has not been fully elucidated. In this study, the mga0357 gene of M. gallisepticum, which encodes TpiA (MGTpiA), was amplified and expressed in Escherichia coli by IPTG induction. The purified recombinant MGTpiA protein exhibited catalytic activity that was similar to TPI from rabbit muscle, reducing NAD(+) to NADH. The MGTpiA was also found to be a surface-exposed protein by western blotting and immunofluorescence assays. In addition, cytadherence inhibition assays confirmed that the cytadherence of M. gallisepticum to the DF-1 cells was significantly inhibited by the anti-MGTpiA serum. The results of the study suggested that MGTpiA plays an important role in the metabolism and closely related to the M. gallisepticum pathogenicity.

Mycoplasma gallisepticum in vivo induced antigens expressed during infection in chickens

Until now only a few genes encoding virulence factors have been characterized in the avian pathogen Mycoplasma gallisepticum. In order to identify candidate targets associated with infection we applied an immunoscreening technique-in vivo induced antigen technology (IVIAT)-to detect immunogens of M. gallisepticum strain Rlow expressed preferentially during in vivo infection. We identified 13 in vivo-induced (IVI) proteins that correspond to different functional categories including: previously reported putative virulence factors (GapA, PlpA, Hlp3, VlhA 1.07 and VlhA 4.01), transport (PotE, MGA_0241 and 0654), translation (L2, L23, ValS), chaperone (GroEL) and a protein with unknown function (MGA_0042). To validate the in vivo antigenic reactivity, 10 IVI proteins were tested by Western blot analysis using serum samples collected from chickens experimentally (with strain Rlow) and naturally (outbreaks, N=3) infected with M. gallisepticum. All IVI proteins tested were immunogenic. To corroborate these results, we tested expression of IVI genes in chickens experimentally infected with M. gallisepticum Rlow, and in MRC-5 human lung fibroblasts cell culture by using relative real time reverse-transcription PCR (RT-PCR). With the exception of MGA_0338, all six genes tested (MGA_1199, 0042, 0654, 0712, 0928 and 0241) were upregulated at least at one time point during experimental infection (2-4 week post-infection). In contrast, the expression of seven out of eight IVI genes (MGA_1199, 0152, 0338, 0042, 0654, 0712, 0928) were downregulated in MRC-5 cell culture at both 2 and 4h PI; MGA_0241 was upregulated 2h PI. Our data suggest that the identified IVI antigens may have important roles in the pathogenesis of M. gallisepticum infection in vivo.

Mycoplasma gallisepticum lipid associated membrane proteins up-regulate inflammatory genes in chicken tracheal epithelial cells via TLR-2 ligation through an NF-κB dependent pathway

Mycoplasma gallisepticum-mediated respiratory inflammation in chickens is associated with accumulation of leukocytes in the tracheal submucosa. However the molecular mechanisms underpinning these changes have not been well described. We hypothesized that the initial inflammatory events are initiated upon ligation of mycoplasma lipid associated membrane proteins (LAMP) to TLRs expressed on chicken tracheal epithelial cells (TEC). To test this hypothesis, live bacteria or LAMPs isolated from a virulent (R_low) or a non-virulent (R_high) strain were incubated with primary TECs or chicken tracheae ex vivo. Microarray analysis identified up-regulation of several inflammatory and chemokine genes in TECs as early as 1.5 hours post-exposure. Kinetic analysis using RT-qPCR identified the peak of expression for most genes to be at either 1.5 or 6 hours. Ex-vivo exposure also showed up-regulation of inflammatory genes in epithelial cells by 1.5 hours. Among the commonly up-regulated genes were IL-1β, IL-6, IL-8, IL-12p40, CCL-20, and NOS-2, all of which are important immune-modulators and/or chemo-attractants of leukocytes. While these inflammatory genes were up-regulated in all four treatment groups, R_low exposed epithelial cells both in vitro and ex vivo showed the most dramatic up-regulation, inducing over 100 unique genes by 5-fold or more in TECs. Upon addition of a TLR-2 inhibitor, LAMP-mediated gene expression of IL-1β and CCL-20 was reduced by almost 5-fold while expression of IL-12p40, IL-6, IL-8 and NOS-2 mRNA was reduced by about 2–3 fold. Conversely, an NF-κB inhibitor abrogated the response entirely for all six genes. miRNA-146a, a negative regulator of TLR-2 signaling, was up-regulated in TECs in response to either R_low or R_high exposure. Taken together we conclude that LAMPs isolated from both R_high and R_low induced rapid, TLR-2 dependent but transient up-regulation of inflammatory genes in primary TECs through an NF-κB dependent pathway.

A sialoreceptor binding motif in the Mycoplasma synoviae adhesin VlhA

Mycoplasma synoviae depends on its adhesin VlhA to mediate cytadherence to sialylated host cell receptors. Allelic variants of VlhA arise through recombination between an assemblage of promoterless vlhA pseudogenes and a single transcription promoter site, creating lineages of M. synoviae that each express a different vlhA allele. The predicted full-length VlhA sequences adjacent to the promoter of nine lineages of M. synoviae varying in avidity of cytadherence were aligned with that of the reference strain MS53 and with a 60-a.a. hemagglutinating VlhA C-terminal fragment from a Tunisian lineage of strain WVU1853^T. Seven different sequence variants of an imperfectly conserved, single-copy, 12-a.a. candidate cytadherence motif were evident amid the flanking variable residues of the 11 total sequences examined. The motif was predicted to adopt a short hairpin structure in a low-complexity region near the C-terminus of VlhA. Biotinylated synthetic oligopeptides representing four selected variants of the 12-a.a. motif, with the whole synthesized 60-a.a. fragment as a positive control, differed (P<0.01) in the extent they bound to chicken erythrocyte membranes. All bound to a greater extent (P<0.01) than scrambled or irrelevant VlhA domain negative control peptides did. Experimentally introduced branched-chain amino acid (BCAA) substitutions Val3Ile and Leu7Ile did not significantly alter binding, whereas fold-destabilizing substitutions Thr4Gly and Ala9Gly tended to reduce it (P<0.05). Binding was also reduced to background levels (P<0.01) when the peptides were exposed to desialylated membranes, or were pre-saturated with free sialic acid before exposure to untreated membranes. From this evidence we conclude that the motif P-X-(BCAA)-X-F-X-(BCAA)-X-A-K-X-G binds sialic acid and likely mediates VlhA-dependent M. synoviae attachment to host cells. This conserved mechanism retains the potential for fine-scale rheostasis in binding avidity, which could be a general characteristic of pathogens that depend on analogous systems of antigenically variable adhesins. The motif may be useful to identify previously unrecognized adhesins.

Factors influencing the cell adhesion and invasion capacity of Mycoplasma gallisepticum

Background

The cell invasiveness of Mycoplasma gallisepticum, the causative agent of respiratory disease in chickens and infectious sinusitis in turkeys, may be a substantial factor in the well-known chronicity of these diseases and in the systemic spread of infection. To date, not much is known about the host factors and mechanisms involved in promotion or obstruction of M. gallisepticum adherence and/or cell invasion.

In the current study, the influence of extracellular matrix (ECM) proteins such as fibronectin, collagen type IV and heparin, as well as plasminogen/plasmin, on the adhesion and cell invasion levels of M. gallisepticum to chicken erythrocytes and HeLa cells was investigated in vitro. Two strains, R_high and R_low, which differ in their adhesion and invasion capacity, were analyzed by applying a modified gentamicin invasion assay. Binding of selected ECM molecules to M. gallisepticum was proven by Western blot analysis.

Results

Collagen type IV, fibronectin, and plasminogen exerted positive effects on adhesion and cell invasion of M. gallisepticum, with varying degrees, depending on the strain used. Especially strain R_high, with its highly reduced cell adhesion and invasion capabilities seemed to profit from the addition of plasminogen. Western and dot blot analyses showed that R_high as well as R_low are able to adsorb horse fibronectin and plasminogen present in the growth medium. Depletion of HeLa cell membranes from cholesterol resulted in increased adhesion, but decreased cell invasion.

Conclusion

ECM molecules seem to play a supportive role in the adhesion/cell invasion process of M. gallisepticum. Cholesterol depletion known to affect lipid rafts on the host cell surface had contrary effects on cell adherence and cell invasion of M. gallisepticum.

P65 truncation impacts P30 dynamics during Mycoplasma pneumoniae gliding

The cell wall-less prokaryote Mycoplasma pneumoniae is a major cause of community-acquired bronchitis and pneumonia in humans. Colonization is mediated largely by a differentiated terminal organelle, which is also the leading end in gliding motility. Cytadherence-associated proteins P30 and P65 appear to traffic concurrently to the distal end of developing terminal organelles. Here, truncation of P65 due to transposon insertion in the corresponding gene resulted in lower gliding velocity, reduced cytadherence, and decreased steady-state levels of several terminal organelle proteins, including P30. Utilizing fluorescent protein fusions, we followed terminal organelle development over time. New P30 foci appeared at nascent terminal organelles in P65 mutants, as in the wild type. However, with forward cell motility, P30 in the P65 mutants appeared to drag toward the trailing cell pole, where it was released, yielding a fluorescent trail to which truncated P65 colocalized. In contrast, P30 was only rarely observed at the trailing end of gliding wild-type cells. Complementation with the recombinant wild-type P65 allele by transposon delivery restored P65 levels and stabilized P30 localization to the terminal organelle.

Detection and differentiation of avian mycoplasmas by surface-enhanced Raman spectroscopy based on a silver nanorod array

Mycoplasma gallisepticum is a bacterial pathogen of poultry that is estimated to cause annual losses exceeding $780 million. The National Poultry Improvement Plan guidelines recommend regular surveillance and intervention strategies to contain M. gallisepticum infections and ensure mycoplasma-free avian stocks, but several factors make detection of M. gallisepticum and diagnosis of M. gallisepticum infection a major challenge. Current techniques are laborious, require special expertise, and are typically plagued by false results. In this study, we describe a novel detection strategy which uses silver nanorod array-surface-enhanced Raman spectroscopy (NA-SERS) for direct detection of avian mycoplasmas. As a proof of concept for use in avian diagnostics, we used NA-SERS to detect and differentiate multiple strains of avian mycoplasma species, including Acholeplasma laidlawii, Mycoplasma gallinarum, Mycoplasma gallinaceum, Mycoplasma synoviae, and M. gallisepticum, including vaccine strains 6/85, F, and ts-11. Chemometric multivariate analysis of spectral data was used to classify these species rapidly and accurately, with >93% sensitivity and specificity. Furthermore, NA-SERS had a lower limit of detection that was 100-fold greater than that of standard PCR and comparable to that of real-time quantitative PCR. Detection of M. gallisepticum in choanal cleft swabs from experimentally infected birds yielded good sensitivity and specificity, suggesting that NA-SERS is applicable for clinical detection.

Effects of sialidase knockout and complementation on virulence of Mycoplasma gallisepticum

Reannotation of the pathogenic Mycoplasma gallisepticum strain R(low) genome identified the hypothetical gene MGA_0329 as a homolog of the sialidase gene MS53_0199 of Mycoplasma synoviae strain MS53. Potent sialidase activity was subsequently quantitated in several M. gallisepticum strains. Because sialidase activity levels correlate significantly with differing M. synoviae strain virulence, we hypothesized this enzyme may also influence the virulence of M. gallisepticum. MGA_0329 was disrupted in strain R(low) to create mutants 6, 358 and P1C5, which resulted in the loss of sialidase activity in all three mutants. Chickens infected with the knockout mutants had significantly less severe (P<0.05) tracheal lesions and tracheal mucosal thickening than chickens infected with equal doses of strain R(low). Significantly fewer (P<0.05) CCU especially of strains 6 and P1C5 were recovered at necropsy. Mini-Tn4001tet plasmid pTF20 carrying a wild-type copy of MGA_0329 with its native promoter was used to complement the genetic lesion in strain P1C5. Three clones derived from P1C5, each having one copy of MGA_0329 stably transposed into a different site in its genome, expressed sialidase restored to wild-type activity levels (1.58×10(-8)U/CFU). Complementation of P1C5 with MGA_0329 did not restore it to wild-type levels of virulence, indicating that the contribution of sialidase to M. gallisepticum virulence is not straightforward.

Mhp182 (P102) binds fibronectin and contributes to the recruitment of plasmin(ogen) to the Mycoplasma hyopneumoniae cell surface

Mycoplasma hyopneumoniae is a major, economically damaging respiratory pathogen. Although M. hyopneumoniae cells bind plasminogen, the identification of plasminogen-binding surface proteins and the biological ramifications of acquiring plasminogen requires further investigation. mhp182 encodes a highly expressed 102 kDa protein (P102) that undergoes proteolytic processing to generate surface-located N-terminal 60 kDa (P60) and C-terminal 42 kDa (P42) proteins of unknown function. We show that recombinant P102 (rP102) binds plasminogen at physiologically relevant concentrations (K(D) ~ 76 nM) increasing the susceptibility of plasmin(ogen) to activation by tissue-specific plasminogen activator (tPA). Recombinant proteins constructed to mimic P60 (rP60) and P42 (rP42) also bound plasminogen at physiologically significant levels. M. hyopneumoniae surface-bound plasminogen was activated by tPA and is able to degrade fibrinogen, demonstrating the biological functionality of M. hyopneumoniae-bound plasmin(ogen) upon activation. Plasmin(ogen) was readily detected in porcine ciliated airways and plasmin levels were consistently higher in bronchoalveolar lavage fluid from M. hyopneumoniae-infected animals. Additionally, rP102 and rP42 bind fibronectin with K(D) s of 26 and 33 nM respectively and recombinant P102 proteins promote adherence to porcine kidney epithelial-like cells. The multifunctional binding ability of P102 and activation of M. hyopneumoniae-sequestered plasmin(ogen) by an exogenous activator suggests P102 plays an important role in virulence.

Role of Mycoplasma pneumoniae glyceraldehyde-3-phosphate dehydrogenase (GAPDH) in mediating interactions with the human extracellular matrix

In different, phylogenetically unrelated micro-organisms, glycolytic enzymes play a dual role. In the cytosol they are involved in metabolic reactions whereas the surface-localized fraction of the enzymes contributes to adhesion and virulence. Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is a typical member of this group of multifunctional proteins. In this study, we characterized the GAPDH of Mycoplasma pneumoniae, a common pathogen of the human respiratory mucosa. Full-length GAPDH of M. pneumoniae was successfully expressed and used to produce a polyclonal antiserum. By immunofluorescence, colony blot and ELISA experiments with different fractions of the M. pneumoniae proteins, GAPDH was demonstrated to be present in the cytosol and at even higher concentrations at the surface of mycoplasmas. Nevertheless, antibodies against recombinant GAPDH were not detected in sera of immunized animals or of patients with confirmed M. pneumoniae infection. Recombinant GAPDH bound to different human cell lines in a concentration-dependent manner, and binding was inhibited by specific anti-GAPDH serum. In contrast, this antiserum did not significantly influence the adherence of M. pneumoniae to HeLa cells. When different human extracellular matrix proteins were tested in Western blot assays, GAPDH bound to fibrinogen. The results showed that the GAPDH of M. pneumoniae is a member of the family of cytosol-localized glycolytic enzymes, which also occur at the surface of the bacterium, and mediates interactions with the extracellular matrix proteins of the human host. Thus, the surface-exposed fraction of GAPDH may be a factor that contributes to the successful colonization of the human respiratory tract by M. pneumoniae.

The Mycoplasma gallisepticum α-enolase is cell surface-exposed and mediates adherence by binding to chicken plasminogen

The α-enolase protein is reported to be an adhesin in several pathogenic bacterial species, but its role in Mycoplasma gallisepticum is unknown. In this study, the M. gallisepticum α-enolase gene was adapted to heterologous expression in Escherichia coli by performing overlapping polymerase chain reaction with site-directed mutagenesis to introduce A960G and A1158G mutations in the nucleotide sequence. The full-length mutated gene was cloned into a pGEM-T Easy vector and subcloned into the expression vector pET32a(+) to construct the pET-rMGEno plasmid. The expression of rMGEno in E. coli strain DE3 was confirmed by sodium dodecyl sulfate polyacrylamide gel electrophoresis with Coomassie blue staining. Purified rMGEno exhibited α-enolase catalytic activity that it could reflect the conversion of NADH to NAD(+). Mouse antiserum to α-enolase was generated by immunization with rMGEno. Immunoblotting and immunofluorescence assay with the antiserum identified α-enolase on the surface of M. gallisepticum cells. Enzyme-linked immunosorbent assay characterized rMGEno as a chicken plasminogen binding protein. An adherence inhibition assay on immortalized chicken fibroblasts (DF-1) demonstrated more than 77% inhibition of adhesion in the presence of mouse antiserum, suggesting that α-enolase of M. gallisepticum participates in bacterial adhesion to DF-1 cells.

Mhp107 is a member of the multifunctional adhesin family of Mycoplasma hyopneumoniae

Mycoplasma hyopneumoniae is the causative pathogen of porcine enzootic pneumonia, an economically significant disease that disrupts the mucociliary escalator in the swine respiratory tract. Expression of Mhp107, a P97 paralog encoded by the gene mhp107, was confirmed using ESI-MS/MS. To investigate the function of Mhp107, three recombinant proteins, F1(Mhp107), F2(Mhp107), and F3(Mhp107), spanning the N-terminal, central, and C-terminal regions of Mhp107 were constructed. Colonization of swine by M. hyopneumoniae requires adherence of the bacterium to ciliated cells of the respiratory tract. Recent studies have identified a number of M. hyopneumoniae adhesins that bind heparin, fibronectin, and plasminogen. F1(Mhp107) was found to bind porcine heparin (K(D) ∼90 nM) in a dose-dependent and saturable manner, whereas F3(Mhp107) bound fibronectin (K(D) ∼180 nM) at physiologically relevant concentrations. F1(Mhp107) also bound porcine plasminogen (K(D) = 24 nM) in a dose-dependent and physiologically relevant manner. Microspheres coated with F3(Mhp107) mediate adherence to porcine kidney epithelial-like (PK15) cells, and all three recombinant proteins (F1(Mhp107)-F3(Mhp107)) bound swine respiratory cilia. Together, these findings indicate that Mhp107 is a member of the multifunctional M. hyopneumoniae adhesin family of surface proteins and contributes to both adherence to the host and pathogenesis.

A processed multidomain mycoplasma hyopneumoniae adhesin binds fibronectin, plasminogen, and swine respiratory cilia

Porcine enzootic pneumonia is a chronic respiratory disease that affects swine. The etiological agent of the disease, Mycoplasma hyopneumoniae, is a bacterium that adheres to cilia of the swine respiratory tract, resulting in loss of cilia and epithelial cell damage. A M. hyopneumoniae protein P116, encoded by mhp108, was investigated as a potential adhesin. Examination of P116 expression using proteomic analyses observed P116 as a full-length protein and also as fragments, ranging from 17 to 70 kDa in size. A variety of pathogenic bacterial species have been shown to bind the extracellular matrix component fibronectin as an adherence mechanism. M. hyopneumoniae cells were found to bind fibronectin in a dose-dependent and saturable manner. Surface plasmon resonance was used to show that a recombinant C-terminal domain of P116 bound fibronectin at physiologically relevant concentrations (K(D) 24 ± 6 nm). Plasmin(ogen)-binding proteins are also expressed by many bacterial pathogens, facilitating extracellular matrix degradation. M. hyopneumoniae cells were found to also bind plasminogen in a dose-dependent and saturable manner; the C-terminal domain of P116 binds to plasminogen (K(D) 44 ± 5 nm). Plasminogen binding was abolished when the C-terminal lysine of P116 was deleted, implicating this residue as part of the plasminogen binding site. P116 fragments adhere to the PK15 porcine kidney epithelial-like cell line and swine respiratory cilia. Collectively these data suggest that P116 is an important adhesin and virulence factor of M. hyopneumoniae.

The ability of disease and non-disease producing strains of Clostridium perfringens from chickens to adhere to extracellular matrix molecules and Caco-2 cells

Clostridium perfringens is a major enteric pathogen that is responsible for causing necrotic enteritis of poultry. The ability to adhere to the host's intestinal epithelium and to extracellular matrix molecules (ECMM) in the gut, are strategies used by numerous bacterial enteropathogens, however, C. perfringens has received comparatively little attention in this respect. The present study investigated sixteen type A C. perfringens isolates from chickens, with varying disease producing ability with respect to necrotic enteritis in chickens, for their ability to adhere to nine different extracellular matrix molecules (ECMM) and to the intestinal epithelial cell line Caco-2. C. perfringens strains were able to bind to ECMMs and there was strain variation. Strains of C. perfringens that produced severe disease, were capable of binding to collagen type III, IV and V, fibrinogen, laminin and vitronectin at higher levels than less severe disease producing strains, suggesting that the ability to adhere to ECMMs might enhance virulence with respect to induction of necrotic enteritis. In addition, severe disease producing strains also bound better to collagen type III and IV and fibrinogen, than non-disease producing strains. The present study also showed that some strains of C. perfringens possessed the ability to adhere to Caco-2 cells; however no relationship was found between the ability to adhere to Caco-2 cells and disease producing ability.

Comparative genomic analyses of attenuated strains of Mycoplasma gallisepticum

Mycoplasma gallisepticum is a significant respiratory and reproductive pathogen of domestic poultry. While the complete genomic sequence of the virulent, low-passage M. gallisepticum strain R (R(low)) has been reported, genomic determinants responsible for differences in virulence and host range remain to be completely identified. Here, we utilize genome sequencing and microarray-based comparative genomic data to identify these genomic determinants of virulence and to elucidate genomic variability among strains of M. gallisepticum. Analysis of the high-passage, attenuated derivative of R(low), R(high), indicated that relatively few total genomic changes (64 loci) occurred, yet they are potentially responsible for the observed attenuation of this strain. In addition to previously characterized mutations in cytadherence-related proteins, changes included those in coding sequences of genes involved in sugar metabolism. Analyses of the genome of the M. gallisepticum vaccine strain F revealed numerous differences relative to strain R, including a highly divergent complement of vlhA surface lipoprotein genes, and at least 16 genes absent or significantly fragmented relative to strain R. Notably, an R(low) isogenic mutant in one of these genes (MGA_1107) caused significantly fewer severe tracheal lesions in the natural host compared to virulent M. gallisepticum R(low). Comparative genomic hybridizations indicated few genetic loci commonly affected in F and vaccine strains ts-11 and 6/85, which would correlate with proteins affecting strain R virulence. Together, these data provide novel insights into inter- and intrastrain M. gallisepticum genomic variability and the genetic basis of M. gallisepticum virulence.

Amino acid changes in elongation factor Tu of Mycoplasma pneumoniae and Mycoplasma genitalium influence fibronectin binding

Mycoplasma pneumoniae and Mycoplasma genitalium are closely related organisms that cause distinct clinical manifestations and possess different tissue predilections despite their high degree of genome homology. We reported earlier that surface-localized M. pneumoniae elongation factor Tu (EF-Tu(Mp)) mediates binding to the extracellular matrix component fibronectin (Fn) through the carboxyl region of EF-Tu. In this study, we demonstrate that surface-associated M. genitalium EF-Tu (EF-Tu(Mg)), in spite of sharing 96% identity with EF-Tu(Mp), does not bind Fn. We utilized this finding to identify the essential amino acids of EF-Tu(Mp) that mediate Fn interactions by generating modified recombinant EF-Tu proteins with amino acid changes corresponding to those of EF-Tu(Mg). Amino acid changes in serine 343, proline 345, and threonine 357 were sufficient to significantly reduce the Fn binding of EF-Tu(Mp). Synthetic peptides corresponding to this region of EF-Tu(Mp) (EF-Tu(Mp) 340-358) blocked both recombinant EF-Tu(Mp) and radiolabeled M. pneumoniae cell binding to Fn. In contrast, EF-Tu(Mg) 340-358 peptides exhibited minimal blocking activity, reinforcing the specificity of EF-Tu-Fn interactions as mediators of microbial colonization and tissue tropism.

Diversifying and stabilizing selection of sialidase and N-acetylneuraminate catabolism in Mycoplasma synoviae

Sialidase activity varies widely among strains and tends to correlate with strain virulence in the avian pathogen Mycoplasma synoviae. To characterize the forms of selection acting on enzymes required for sialic acid scavenging and catabolism, the ratios of nonsynonymous (K(a)) to synonymous (K(s)) mutation frequency were calculated for codons in the sialidase gene of 16 strains of M. synoviae and for its nearly identical homolog in four strains of Mycoplasma gallisepticum. The K(a)/K(s) (omega) values for the linked genes required for nutritive N-acetylneuraminate catabolism (nanA, nagC, nanE, nagA, and nagB) from nine strains of M. synoviae were also determined. To provide context, omega was determined for all corresponding genes of 26 strains of Clostridium perfringens and Streptococcus pneumoniae. Bayesian models of sequence evolution showed that only the sialidase of M. synoviae was under significant (P < 0.001) diversifying selection, while the M. synoviae genes for N-acetylneuraminate catabolism and all genes examined from M. gallisepticum, C. perfringens, and S. pneumoniae were under neutral to stabilizing selection. Diversifying selection acting on the sialidase of M. synoviae, but not on the sialidase of M. gallisepticum or the sialidases or other enzymes essential for sialic acid scavenging in other Firmicutes, is evidence that variation in specific activity of the enzyme is perpetuated by a nonnutritive function in M. synoviae that is influenced by the genomic context of the organism.

Cytoskeletal asymmetrical dumbbell structure of a gliding mycoplasma, Mycoplasma gallisepticum, revealed by negative-staining electron microscopy

Several mycoplasma species feature a membrane protrusion at a cell pole, and unknown mechanisms provide gliding motility in the direction of the pole defined by the protrusion. Mycoplasma gallisepticum, an avian pathogen, is known to form a membrane protrusion composed of bleb and infrableb and to glide. Here, we analyzed the gliding motility of M. gallisepticum cells in detail. They glided in the direction of the bleb at an average speed of 0.4 microm/s and remained attached around the bleb to a glass surface, suggesting that the gliding mechanism is similar to that of a related species, Mycoplasma pneumoniae. Next, to elucidate the cytoskeletal structure of M. gallisepticum, we stripped the envelopes by treatment with Triton X-100 under various conditions and observed the remaining structure by negative-staining transmission electron microscopy. A unique cytoskeletal structure, about 300 nm long and 100 nm wide, was found in the bleb and infrableb. The structure, resembling an asymmetrical dumbbell, is composed of five major parts from the distal end: a cap, a small oval, a rod, a large oval, and a bowl. Sonication likely divided the asymmetrical dumbbell into a core and other structures. The cytoskeletal structures of M. gallisepticum were compared with those of M. pneumoniae in detail, and the possible protein components of these structures were considered.

New insights into the pathogenesis and detection of Mycoplasma pneumoniae infections

Mycoplasma pneumoniae is a common cause of upper and lower respiratory tract infections in persons of all ages and may be responsible for up to 40% of community-acquired pneumonias. A wide array of extrapulmonary events may accompany the infections caused by this organism, related to autoimmunity or direct spread. This review includes a discussion of the latest knowledge concerning the molecular pathological basis of mycoplasmal respiratory disease, how the organism interacts with the host immune system and its association with the development of chronic conditions such as asthma, recent emergence of macrolide resistance and the status of laboratory diagnostic methods.

The C-terminal variable domain of LigB from Leptospira mediates binding to fibronectin

Adhesion through microbial surface components that recognize adhesive matrix molecules is an essential step in infection for most pathogenic bacteria. In this study, we report that LigB interacts with fibronectin (Fn) through its variable region. A possible role for LigB in bacterial attachment to host cells during the course of infection is supported by the following observations: (i) binding of the variable region of LigB to Madin-Darby canine kidney (MDCK) cells in a dose-dependent manner reduces the adhesion of Leptospira, (ii) inhibition of leptospiral attachment to Fn by the variable region of LigB, and (iii) decrease in binding of the variable region of LigB to the MDCK cells in the presence of Fn. Furthermore, we found a significant reduction in binding of the variable region of LigB to Fn using small interfering RNA (siRNA). Finally, the isothermal titration calorimetric results confirmed the interaction between the variable region of LigB and Fn. This is the first report to demonstrate that LigB binds to MDCK cells. In addition, the reduction of Fn expression in the MDCK cells, by siRNA, reduced the binding of LigB. Taken together, the data from the present study showed that LigB is a Fn-binding protein of pathogenic Leptospira spp. and may play a pivotal role in Leptospira-host interaction during the initial stage of infection.

Epidemiology, clinical manifestations, pathogenesis and laboratory detection of Mycoplasma pneumoniae infections

Since its initial description in the 1940s and eventual elucidation as a highly evolved pathogenic bacterium, Mycoplasma pneumoniae has come to be recognized as a worldwide cause of primary atypical pneumonia. Beyond its ability to cause severe lower respiratory illness and milder upper respiratory symptoms it has become apparent that a wide array of extrapulmonary infectious and postinfectious events may accompany the infections in humans caused by this organism. Autoimmune disorders and chronic diseases such as asthma and arthritis are increasingly being associated with this mycoplasma, which frequently persists in individuals for prolonged periods. The reductive evolutionary process that has led to the minimal genome of M. pneumoniae suggests that it exists as a highly specialized parasitic bacterium capable of residing in an intracellular state within the respiratory tissues, occasionally emerging to produce symptoms. This review includes discussion of some of the newer aspects of our knowledge on this pathogen, characteristics of clinical infections, how it causes disease, the recent emergence of macrolide resistance, and the status of laboratory diagnostic methods.

Deletion of the Mycoplasma genitalium MG_217 gene modifies cell gliding behaviour by altering terminal organelle curvature

Motility is often a virulence factor of pathogenic bacteria. Although recent works have identified genes involved in gliding motility of mycoplasmas, little is known about the mechanisms governing the cell gliding behaviour. Here, we report that Mycoplasma genitalium MG217 is a novel protein involved in the gliding apparatus of this organism and it is, at least, one of the genes that are directing cells to move in narrow circles when they glide. In the absence of MG_217 gene, cells are still able to glide but they mainly move drawing erratic or wide circular paths. This change in the gliding behaviour correlates with a rearrangement in the terminal organelle disposition, suggesting that the terminal organelle operates as a guide to steer the mycoplasma cell in a specific direction. Immunogold labelling reveals that MG217 protein is located intracellular at the distal end of the terminal organelle, between the cell membrane and the terminal button. Such location is consistent with the idea that MG217 could act as a modulator of the terminal organelle curvature, allowing cells to move in specific directions.

The Mycoplasma gallisepticum OsmC-like protein MG1142 resides on the cell surface and binds heparin

Mycoplasma gallisepticum is an avian pathogen that causes a chronic respiratory disease of chickens and results in significant economic losses to the poultry industry worldwide. Colonization of the host and the establishment of chronic disease are initiated by the cytadherence of M. gallisepticum to the host respiratory epithelium. While several proteins involved in cytadhesion have been characterized, molecules that interact with components of the host extracellular matrix, a process that is central to pathogenesis, are only now being identified. In this study, M. gallisepticum whole cells were shown to bind heparin in a specific and saturable manner. Heparin also significantly inhibited the binding of M. gallisepticum to the human lung fibroblast cell line MRC-5, suggesting a potential role for glycosaminoglycans (GAGs) in cytadherence. M. gallisepticum protein MG1142 (encoded by mga 1142), which displays homology to the osmotically induced (OsmC) family of proteins, binds strongly to heparin, is highly expressed during in vitro culture, and is surface accessible. Recombinant MG1142 bound heparin in a dose-dependent and saturable manner with a dissociation constant (K(d)) of 10+/-1.8 nM, which is within a physiologically significant range, compared to that of other heparin-binding proteins. Binding to heparin was inhibited by the heavily sulfated polysaccharide fucoidan, but not by mucin or chondroitin sulfate A or B, suggesting that electrostatic interactions between the sulfate groups of heparin and the positively charged basic residues of the MG1142 protein are important in binding. The ability of M. gallisepticum to bind GAGs may contribute to host adherence and colonization.

Mycoplasma gallisepticum invades chicken erythrocytes during infection

Recently, it was demonstrated using in vitro assays that the avian pathogen Mycoplasma gallisepticum is able to invade nonphagocytic cells. It was also shown that this mycoplasma can survive and multiply intracellularly for at least 48 h and that this cell invasion capacity contributes to the systemic spread of M. gallisepticum from the respiratory tract to the inner organs. Using the gentamicin invasion assay and a differential immunofluorescence technique combined with confocal laser scanning microscopy, we were able to demonstrate in in vitro experiments that M. gallisepticum is also capable of invading sheep and chicken erythrocytes. The frequencies of invasion of three well-defined M. gallisepticum strains were examined over a period of 24 h, and a significant increase in invasiveness occurred after 8 h of infection. In addition, blood samples derived from chickens experimentally infected via the aerosol route with the virulent strain M. gallisepticum R(low) were analyzed. Surprisingly, M. gallisepticum R(low) was detected in the bloodstream of infected chickens by nested PCR, as well as by differential immunofluorescence and interference contrast microscopy that showed that mycoplasmas were not only on the surface but also inside chicken erythrocytes. This finding provides novel insight into the pathomechanism of M. gallisepticum and may have implications for the development of preventive strategies.

Ultrastructure and gliding motility of Mycoplasma amphoriforme, a possible human respiratory pathogen

Despite their small size and reduced genomes, many mycoplasma cells have complex structures involved in virulence. Mycoplasma pneumoniae has served as a model for the study of virulence factors of a variety of mycoplasma species that cause disease in humans and animals. These cells feature an attachment organelle, which mediates cytadherence and gliding motility and is required for virulence. An essential component of the architecture of the attachment organelle is an internal detergent-insoluble structure, the electron-dense core. Little information is known regarding its underlying mechanisms. Mycoplasma amphoriforme, a close relative of both M. pneumoniae and the avian pathogen Mycoplasma gallisepticum, is a recently discovered organism associated with chronic bronchitis in immunosuppressed individuals. This work describes both the ultrastructure of M. amphoriforme strain A39T as visualized by scanning electron microscopy and the gliding motility characteristics of this organism on glass. Though externally resembling M. gallisepticum, M. amphoriforme cells were found to have a Triton X-100-insoluble structure similar to the M. pneumoniae electron-dense core but with different dimensions. M. amphoriforme also exhibited gliding motility using time-lapse microcinematography; its movement was slower than that of either M. pneumoniae or M. gallisepticum.