MSG1, a surface-localised protein of Mycoplasma suis is involved in the adhesion to erythrocytes

Mycoplasma suis Alpha-Enolase Subunit Vaccine Induces an Immune Response in Experimental Animals

Recombinant protein technology has emerged as an excellent option for vaccine development. However, prior to our study, the immune induction ability of recombinant Mycoplasma suis alpha-enolase (rMseno) in animals remained unclear. The purpose of this study was to develop a rMseno protein subunit vaccine and to determine its ability to elicit an immunological response. To accomplish this, we cloned the gene into pET-15b, expressed it in BL21 cells, and purified it. Following the establishment of immunity, the immunogenicity and potential for protection of rMseno were evaluated in mice and piglets. The results demonstrate that anti-M. suis serum recognized the pure rMseno protein in both mice and piglets as evidenced by high levels of specific anti-rMseno antibodies, significantly increased levels of IFN-γ and IL-4 cytokines, and significantly increased T lymphocyte proliferation index. Piglets also had significantly increased levels of specific IgG₁, IgG_2a, CD4⁺, and CD8⁺ cells. The rMseno findings demonstrated a robust immunological response in mice and piglets, affording partial clinical protective efficacy in piglets.

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) moonlights as an adhesin in Mycoplasma hyorhinis adhesion to epithelial cells as well as a plasminogen receptor mediating extracellular matrix degradation

Mycoplasma hyorhinis infects pigs causing polyserositis and polyarthritis, and has also been reported in a variety of human tumor tissues. The occurrence of disease is often linked with the systemic invasion of the pathogen. Glyceraldehyde-3-Phosphate Dehydrogenase (GAPDH), one of the key enzymes of glycolysis, was reported as a surface multifunctional molecule in several bacteria. Here, we investigated whether GAPDH could manifest binary functions; as an adhesin to promote colonization as well as a plasminogen receptor functioning in extracellular matrix (ECM) degradation to promote systemic invasion. The surface localization of GAPDH was observed in M. hyorhinis with flow cytometry and colony blot analysis. Recombinant GAPDH (rGAPDH) was found to be able to bind porcine-derived PK-15 and human-derived NCI-H292 cells. The incubation with anti-GAPDH antibody significantly decreased the adherence of M. hyorhinis to both cell lines. To investigate its function in recruiting plasminogen, firstly, the interaction between rGAPDH and plasminogen was demonstrated by ELISA and Far-Western blot assay. The activation of the rGAPDH-bound plasminogen into plasmin was proved by using a chromogenic substrate, and furtherly confirmed to degrade extracellular matrix by using a reconstituted ECM. Finally, the ability of rGAPDH to bind different ECM components was demonstrated, including fibronectin, laminin, collagen type IV and vitronectin. Collectively, our data imply GAPDH as an important adhesion factor of M. hyrohinis and a receptor for hijacking host plasminogen to degrade ECM. The multifunction of GAPDH to bind both plasminogen and ECM components is believed to increase the targeting of proteolysis and facilitate the dissemination of M. hyorhinis.

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.

Persistence in Livestock Mycoplasmas—a Key Role in Infection and Pathogenesis

Purpose of Review

Mycoplasma, economically important pathogens in livestock, often establishes immunologically complex persistent infections that drive their pathogenesis and complicate prophylaxis and therapy of the caused diseases. In this review, we summarize some of the recent findings concerning cellular and molecular persistence mechanisms related to the pathogenesis of mycoplasma infections in livestock.

Recent Findings

Data from recent studies prove several mechanisms including intracellular lifestyle, immune dysregulation, and autoimmunity as well as microcolony and biofilm formation and apoptosis of different host cell types as important persistence mechanisms in several clinically significant Mycoplasma species, i.e., M. bovis, M. gallisepticum, M. hyopneumoniae, and M. suis.

Summary

Evasion of the immune system and the establishment of persistent infections are key features in the pathogenesis of livestock mycoplasmas. In-depth knowledge of the underlying mechanisms will provide the basis for the development of therapy and prophylaxis strategies against mycoplasma infections.

Formylated N-terminal methionine is absent from the Mycoplasma hyopneumoniae proteome: Implications for translation initiation

N-terminal methionine excision (NME) is a proteolytic pathway that cleaves the N-termini of proteins, a process that influences where proteins localise in the cell and their turnover rates. In bacteria, protein biosynthesis is initiated by formylated methionine start tRNA (fMet-tRNA_f^Met). The formyl group is attached by formyltransferase (FMT) and is subsequently removed by peptide deformylase (PDF) in most but not all proteins. Methionine aminopeptidase then cleaves deformylated methionine to complete the process. Components of NME, particularly PDF, are promising therapeutic targets for bacterial pathogens. In Mycoplasma hyopneumoniae, a genome-reduced, major respiratory pathogen of swine, pdf and fmt are absent from its genome. Our bioinformatic analysis uncovered additional enzymes involved in formylated N-terminal methionine (fnMet) processing missing in fourteen mycoplasma species, including M. hyopneumoniae but not in Mycoplasma pneumoniae, a major respiratory pathogen of humans. Consistent with our bioinformatic studies, an analysis of in-house tryptic peptide libraries confirmed the absence of fnMet in M. hyopneumoniae proteins but, as expected fnMet peptides were detected in the proteome of M. pneumoniae. Additionally, computational molecular modelling of M. hyopneumoniae translation initiation factors reveal structural and sequence differences in areas known to interact with fMet-tRNA_f^Met. Our data suggests that some mycoplasmas have evolved a translation process that does not require fnMet.

Characterization of Mycoplasma gallisepticum pyruvate dehydrogenase alpha and beta subunits and their roles in cytoadherence

Mycoplasma gallisepticum is a causative agent of chronic respiratory disease in chickens, typically causing great economic losses. Cytoadherence is the critical stage for mycoplasma infection, and the associated proteins are important for mycoplasma pathogenesis. Many glycolytic enzymes are localized on the cell surface and can bind the extracellular matrix of host cells. In this study, the M. gallisepticum pyruvate dehydrogenase E1 alpha subunit (PDHA) and beta subunit (PDHB) were expressed in Escherichia coli, and their enzymatic activities were identified based on 2,6-dichlorophenol indophenol reduction. When recombinant PDHA (rPDHA) and recombinant PDHB (rPDHB) were mixed at a 1:1 molar ratio, they exhibited strong enzymatic activity. Alone, rPDHA and rPDHB exhibited no or weak enzymatic activity. Further experiments indicated that both PDHA and PDHB were surface-exposed immunogenic proteins of M. gallisepticum. Bactericidal assays showed that the mouse anti-rPDHA and anti-rPDHB sera killed 48.0% and 75.1% of mycoplasmas respectively. A combination of rPDHA and rPDHB antisera had a mean bactericidal rate of 65.2%, indicating that rPDHA and rPDHB were protective antigens, and combining the two sera did not interfere with bactericidal activity. Indirect immunofluorescence and surface display assays showed that both PDHA and PDHB adhered to DF-1 chicken embryo fibroblast cells and adherence was significantly inhibited by antisera against PDHA and PDHB. Adherence inhibition of M. gallisepticum to DF-1 chicken embryo fibroblast cells was 30.2% for mouse anti-rPDHA serum, 45.1% for mouse anti-rPDHB serum and 72.5% for a combination of rPDHA and rPDHB antisera, suggesting that rPDHA and rPDHB antisera may have synergistically interfered with M. gallisepticum cytoadherence. Plasminogen (Plg)-binding assays further demonstrated that both PDHA and PDHB were Plg-binding proteins, which may have contributed to bacterial colonization. Our results clarified the enzymatic activity of M. gallisepticum PDHA and PDHB and demonstrated these compounds as Plg-binding proteins involved in cytoadherence.

Identification of erythrocyte membrane proteins interacting with Mycoplasma suis GAPDH and OSGEP

Mycoplasma suis (M. suis) is an uncultivable haemotrophic mycoplasma that parasitizes the red blood cells of a wide range of domestic and wild animals. Adhesion of M. suis to host erythrocytes is crucial for its unique RBC-dependent lifecycle. MSG1 protein (now named as GAPDH) with homology to glyceraldehyde-3-phosphate dehydrogenase (GAPDH) was the first identified adhesion protein of M. suis. In this study, we found that O-sialoglycoprotein endopeptidase (OSGEP) is another M. suis protein capable of binding porcine erythrocytes. Recombinant OSGEP expressed in E. coli demonstrated surface localization similar to GAPDH. Purified rOSGEP bound to erythrocyte membrane preparations in a dose-dependent manner and this adhesion could be specifically inhibited by anti-rOSGEP antibodies. E. coli transformants expressing OSGEP on their surface were able to adhere to porcine erythrocytes. Furthermore, using far-western and pull-down assays, we determined the host membrane proteins that interacted with OSGEP and GAPDH were Band3 and glycophorin A (GPA). In conclusion, our studies indicated that OSGEP and GAPDH could interact with both Band3 and GPA to mediate adhesion of M. suis to porcine erythrocytes.

Quantitative analysis of Mycoplasma wenyonii and 'Candidatus Mycoplasma haemobos" infections in cattle using novel gapN-based realtime PCR assays

Hemotrophic mycoplasmas (HMs) are associated with anemia and other disease complexes in a wide range of livestock and wild animals. Two bovine HM species have been identified to date, i.e. Mycoplasma wenyonii and 'Candidatus Mycoplasma haemobos'. The study aim was to develop quantitative real-time PCR assays (qPCRs) to detect and quantify M. wenyonii and 'C. M. haemobos' and to apply these assays to DNA samples extracted from bovine blood collected in Germany (n = 220) from 22 herds. The qPCR assays specific for M. wenyonii and 'C. M. haemobos' were designed using the gapN of the respective hemoplasma species as gene target which encodes the NADP-dependent glyceraldehyde 3-phosphate dehydrogenases (GAPN). The sensitivity of both assays was 10 genome equivalents per reaction, corresponding to 2500 genome equivalents per ml blood. No cross-reactivity with non-target bovine HMs. and other bovine pathogens was observed. Bovine HM DNA was detected in 137 samples (62.27%) with 118 samples (53.64%) being positive for 'C.M. haemobos' and 19 samples (8.64%) being positive for M. wenyonii. Thereof, 11 animals (5.00%) were co-infected with both bovine HM species. The found herd prevalence for `C. M. haemobos` was 100.00%, and for M. wenyonii 36.36% with mean bacterial loads of 3.7 × 10⁷ `C. M. haemobos`/mL blood and of 4.29 × 10⁵M. wenyonii/mL blood respectively. Clinical and economic relevance of bovine HM species should be goal of future studies for which the novel gapN qPCR assays can serve as a valuable diagnostic tool.

Interactions of surface-displayed glycolytic enzymes of Mycoplasma pneumoniae with components of the human extracellular matrix

Mycoplasma pneumoniae is a major cause of community-acquired respiratory infections worldwide. Due to the strongly reduced genome, the number of virulence factors expressed by this cell wall-less pathogen is limited. To further understand the processes during host colonization, we investigated the interactions of the previously confirmed surface-located glycolytic enzymes of M. pneumoniae (pyruvate dehydrogenase A-C [PdhA-C], glyceraldehyde-3-phosphate dehydrogenase [GapA], lactate dehydrogenase [Ldh], phosphoglycerate mutase [Pgm], pyruvate kinase [Pyk] and transketolase [Tkt]) to the human extracellular matrix (ECM) proteins fibrinogen (Fn), fibronectin (Fc), lactoferrin (Lf), laminin (Ln) and vitronectin (Vc), respectively. Concentration-dependent interactions between Fn and Vc and all eight recombinant proteins derived from glycolytic enzymes, between Ln and PdhB-C, GapA, Ldh, Pgm, Pyk and Tkt, between Lf and PdhA-C, GapA and Pyk, and between Fc and PdhC and GapA were demonstrated. In most cases, these associations are significantly influenced by ionic forces and by polyclonal sera against recombinant proteins. In immunoblotting, the complex of human plasminogen, activator (tissue-type or urokinase plasminogen activator) and glycolytic enzyme was not able to degrade Fc, Lf and Ln, respectively. In contrast, degradation of Vc was confirmed in the presence of all eight enzymes tested. Our data suggest that the multifaceted associations of surface-localized glycolytic enzymes play a potential role in the adhesion and invasion processes during infection of human respiratory mucosa by M. pneumoniae.

Updating the proteome of the uncultivable hemotrophic Mycoplasma suis in experimentally infected pigs

Mycoplasma suis belongs to the hemotrophic mycoplasmas that are associated with acute and chronic anemia in a wide range of livestock and wild animals. The inability to culture M. suis in vitro has hindered its characterization at the molecular level. Since the publication of M. suis genome sequences in 2011 only one proteome study has been published. Aim of the presented study was to significantly extend the proteome coverage of M. suis strain KI_3806 during acute infection by applying three different protein extraction methods followed by 1D SDS-PAGE and LC-MS/MS. A total of 404 of 795 M. suis KI_3806 proteins (50.8%) were identified. Data analysis revealed the expression of 83.7% of the predicted ORFs with assigned functions but also highlights the expression of 179 of 523 (34.2%) hypothetical proteins with unknown functions. Computational analyses identified expressed membrane-associated hypothetical proteins that might be involved in adhesion or host-pathogen interaction. Furthermore, analyses of the expressed proteins indicated the existence of a hexose-6-phosphate-transporter and an ECF transporter. In conclusion, our proteome study provides a further step toward the elucidation of the unique life cycle of M. suis and the establishment of an in vitro culture. All MS data have been deposited in the ProteomeXchange with identifier PXD002294 (http://proteomecentral.proteomexchange.org/dataset/PXD002294).

Network of Surface-Displayed Glycolytic Enzymes in Mycoplasma pneumoniae and Their Interactions with Human Plasminogen

In different bacteria, primarily cytosolic and metabolic proteins are characterized as surface localized and interacting with different host factors. These moonlighting proteins include glycolytic enzymes, and it has been hypothesized that they influence the virulence of pathogenic species. The presence of surface-displayed glycolytic enzymes and their interaction with human plasminogen as an important host factor were investigated in the genome-reduced and cell wall-less microorganism Mycoplasma pneumoniae, a common agent of respiratory tract infections of humans. After successful expression of 19 glycolytic enzymes and production of polyclonal antisera, the localization of proteins in the mycoplasma cell was characterized using fractionation of total proteins, colony blot, mild proteolysis and immunofluorescence of M. pneumoniae cells. Eight glycolytic enzymes, pyruvate dehydrogenases A to C (PdhA-C), glyceraldehyde-3-phosphate dehydrogenase (GapA), lactate dehydrogenase (Ldh), phosphoglycerate mutase (Pgm), pyruvate kinase (Pyk), and transketolase (Tkt), were confirmed as surface expressed and all are able to interact with plasminogen. Plasminogen bound to recombinant proteins PdhB, GapA, and Pyk was converted to plasmin in the presence of urokinase plasminogen activator and plasmin-specific substrate d-valyl-leucyl-lysine-p-nitroanilide dihydrochloride. Furthermore, human fibrinogen was degraded by the complex of plasminogen and recombinant protein PdhB or Pgm. In addition, surface-displayed proteins (except PdhC) bind to human lung epithelial cells, and the interaction was reduced significantly by preincubation of cells with antiplasminogen. Our results suggest that plasminogen binding and activation by different surface-localized glycolytic enzymes of M. pneumoniae may play a role in successful and long-term colonization of the human respiratory tract.

Glyceradehyde-3-phosphate dehydrogenase as a suitable vaccine candidate for protection against bacterial and parasitic diseases

The enzyme glyceraldehyde-3-P-dehydrogenase (GAPDH) has been identified as having other properties in addition to its key role in glycolysis. The ability of GAPDH to bind to numerous extracellular matrices, modulation of host-immune responses, a role in virulence and surface location has prompted numerous investigators to postulate that GAPDH may be a good vaccine candidate for protection against numerous pathogens. Although immune responses against GAPDH have been described for many microorganisms, vaccines containing GAPDH have been successfully tested in few cases including those against the trematode-Schistosoma mansoni, the helminth-Enchinococcus multilocularis; the nematode filaria- Litomosoides sigmodontis; fish pathogens such as Aeromonas spp., Vibrio spp., Edwarsiella spp., and Streptococcus iniae; and environmental streptococci, namely, Streptococcus uberis and Streptococcus dysgalactiae. Before GAPDH-based vaccines are considered viable options for protection against numerous pathogens, we need to take into account the homology between the host and pathogen GAPDH proteins to prevent potential autoimmune reactions, thus protective GAPDH epitopes unique to the pathogen protein must be identified.

Expression and immunological characteristics of the surface-localized pyruvate kinase in Mycoplasma gallisepticum

The widespread avian pathogen Mycoplasma gallisepticum is a causative agent of respiratory disease. The wall-less prokaryotes lack some tricarboxylic acid cycle enzymes, therefore, the glycolysis metabolic pathway is of great importance to these organisms. Pyruvate kinase (PK) is one of the key enzymes of the glycolytic pathway, and its immunological characteristics in Mycoplasma are not well known. In this study, the M. gallisepticum pyruvate kinase fusion protein (PykF) was expressed in a pET system. The full-length of the gene was subcloned into the expression vector pET28a(+) to construct the pET28a-rMGPykF plasmid, which was then transformed into Escherichia coli strain BL21 (DE3) cells. The expression of the 62 kDa recombinant protein of rMGPykF in E. coli strain BL21 (DE3) was confirmed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis with Coomassie blue staining. Purified rMGPykF exhibited PK catalytic activity, which could reflect the conversion of NADH to NAD(+). Mouse anti-PykF antibodies were generated by immunization of mice with rMGPykF. Immunoblot and immunoelectron microscopy assays identified PykF as an immunogenic protein expressed on the surface of M. gallisepticum cells. Bactericidal assay showed that anti-rMGPykF antiserum killed 70.55% of M. gallisepticum cells, suggesting the protective potential of PykF. Adherence inhibition assay on immortalized chicken fibroblasts (DF-1) cells revealed more than 39.31% inhibition of adhesion in the presence of anti-rMGPykF antiserum, suggesting that PykF of M. gallisepticum participates in bacterial adhesion to DF-1 cells.

Identification of B cell epitopes in the MSG1 protein of Mycoplasma suis

Mycoplasma suis (M. suis) is an extracellular bacterial organism that attaches to and causes deformity and damage to porcine red blood cells. M. suis glyceraldehyde-3-phosphate dehydrogenase-like protein 1 (MSG1), a membrane-associated adhesion protein, plays a major role in M. suis attachment and infection of porcine erythrocytes. In order to identify the epitopes in MSG1 protein of M. suis, recombinant MSG1 (rMSG1) expressed in Escherichia coli Top10 was purified with affinity chromatography and used to immunize BALB/c mice to prepare and screen monoclonal antibodies (MAbs). Western blot results showed that 1C10, 2F10, 4G10, and 10E9 can specifically react with recombinant MSG1 and M. suis. Moreover, 23 truncated fragments of MSG1 were amplified and cloned into pET-32a vector and induced by IPTG. Different recombinant truncated proteins were used to identify B cell epitopes in the rMSG1 protein. Epitope mapping revealed that MAb 1C10 recognizes the linear epitope D(291)THGSVF(297); MAb 2F10 recognizes the linear epitope L(251)CLKI(255); and MAbs 4G10 and 10E9 recognize the linear epitope I(268)KDGENE(274). The alignment of MSG1 epitope sequences with that of different M. suis strains accessed on NCBI showed that one epitope is highly conserved in M. suis strains. This research is the first to examine the epitopes in MSG1 of M. suis and demonstrate the variations of epitopes.

Subunits of the Pyruvate Dehydrogenase Cluster of Mycoplasma pneumoniae Are Surface-Displayed Proteins that Bind and Activate Human Plasminogen

The dual role of glycolytic enzymes in cytosol-located metabolic processes and in cell surface-mediated functions with an influence on virulence is described for various micro-organisms. Cell wall-less bacteria of the class Mollicutes including the common human pathogen Mycoplasma pneumoniae possess a reduced genome limiting the repertoire of virulence factors and metabolic pathways. After the initial contact of bacteria with cells of the respiratory epithelium via a specialized complex of adhesins and release of cell-damaging factors, surface-displayed glycolytic enzymes may facilitate the further interaction between host and microbe. In this study, we described detection of the four subunits of pyruvate dehydrogenase complex (PDHA-D) among the cytosolic and membrane-associated proteins of M. pneumoniae. Subunits of PDH were cloned, expressed and purified to produce specific polyclonal guinea pig antisera. Using colony blotting, fractionation of total proteins and immunofluorescence experiments, the surface localization of PDHA-C was demonstrated. All recombinant PDH subunits are able to bind to HeLa cells and human plasminogen. These interactions can be specifically blocked by the corresponding polyclonal antisera. In addition, an influence of ionic interactions on PDHC-binding to plasminogen as well as of lysine residues on the association of PDHA-D with plasminogen was confirmed. The PDHB subunit was shown to activate plasminogen and the PDHB-plasminogen complex induces degradation of human fibrinogen. Hence, our data indicate that the surface-associated PDH subunits might play a role in the pathogenesis of M. pneumoniae infections by interaction with human plasminogen.

Identification of Mycoplasma suis MSG1 interaction proteins on porcine erythrocytes

Adhesion protein MSG1 mediating adherence to porcine erythrocytes in Mycoplasma suis (M. suis) invasion has been identified previously. In order to determine the host membrane proteins that interact with MSG1, recombinant His-tagged MSG1 (rMSG1) was used to screen for interacting proteins in the protein extracts of porcine erythrocyte membrane. Potential rMSG1-interacting proteins were initially identified as band 3 and β-actin with molecular weight of 46 and 45 kDa, respectively. Immune fluorescence results showed that rMSG1 can specifically bind with the β-actin of HeLa, BHK-21, and HEK-293A cells, respectively. RNA interference assays further demonstrated that the interaction between β-actin and rMSG1 on HeLa cells was specific and dose dependent. Confocal microscopy showed that both rMSG1 and M. suis can partially co-localize with β-actin on the surface of porcine erythrocytes. Pull-down assays showed that rMSG1 can directly interact with β-actin. Our study is the first to report the interaction of MSG1 with β-actin, which will be of help to understand the pathogenesis of M. suis and develop a cultivation system.

Pathobiology of Mycoplasma suis

Mycoplasma suis is an uncultivable bacterium lacking a cell wall that attaches to and may invade the red blood cells of pigs. M. suis infections occur worldwide and cause the pig industry serious economic losses due to the disease known as infectious anaemia of pigs or, historically, porcine eperythrozoonosis. Infectious anaemia of pigs is characterised predominantly by acute haemolytic or chronic anaemia, along with non-specific manifestations, such as growth retardation in feeder pigs and poor reproductive performance in sows. The fastidious nature of M. suis, as well as the lack of an in vitro cultivation system, has hampered the understanding of the biology and pathogenicity of this organism. Pathogenetic mechanisms of M. suis include direct destruction of red blood cells by adhesion, invasion, nutrient scavenging, immune-mediated lysis and eryptosis, as well as endothelial targeting. Recently published genome sequences, in combination with proteome analyses, have generated new insights into the pathogenicity of M. suis. The present review combines these data with the knowledge provided by experimental M. suis infections.

Interactive host cells related to Mycoplasma suis α-enolase by yeast two-hybrid analysis

Mycoplasma suis belongs to the haemotrophic mycoplasmas, which colonise the red blood cells of a wide range of vertebrates. Adhesion to red blood cells is the crucial step in the unique lifecycle of M. suis. In addition to MSG1 protein, α-enolase is the second adhesion protein of M. suis, and may be involved in the adhesion of M. suis to porcine red blood cells (RBC). To simulate the environment of the RBC, we established the cDNA library of swine peripheral blood mononuclear cells (PBMC). The yeast two-hybrid (Y2H) system was adopted to screen α-enolase interactive proteins in the PBMC line. Alignment with the NCBI database revealed four interactive proteins: beta-actin, 60S ribosomal protein L11, clusterin precursor and endonuclease/reverse transcriptase. However, the M. suis α-enolase interactive proteins in the PBMC cDNA library obtained in the current study provide valuable information about the host cell interactions of the M. suis α-enolase protein.

Seroprevalence and risk factors of Mycoplasma suis infection in pig farms in central China

Mycoplasma suis, the causative agent of porcine infectious anemia, causes large economic losses to the swine industry worldwide. A questionnaire-based survey was conducted in 69 pig farms in Hubei Province, China, from November 2011 to August 2013 to ascertain the prevalence and associated risk factors of M. suis. Four thousand and four blood samples from pigs of all the age groups were tested for M. suis antibodies using the established rMSG1-ELISA assay. Among these 4004 samples, 1615 blood samples from multiparous sows were examined to identify the association between seroprevalence and different seasons. Information on risk factors collected from farmers or attending veterinarians was recorded on a pre-designed questionnaire. The overall test seroprevalence of M. suis infection at the animal level was 31.9% (1277/4004; 95% CI: 30.5%, 33.4%), whereas at the farm level, this value was 95.65% (66/69; 95% CI: 87.8%, 99.1%). The seroprevalence of M. suis was higher in replacement gilts (40.6%; 95% CI: 35.1%, 46.3%), multiparous sows (48.2%; 95% CI: 45.8%, 50.7%) and boars (44.4%; 95% CI: 34.5%, 54.8%), as compared to piglets (13.0%; 95% CI: 9.4%, 17.3%), weaned-piglets (10.8%; 95% CI: 8.9%, 13.0%), and growing-finishing pigs (25.0%; 95% CI: 22.0%, 28.3%). In terms of seasons, the prevalence of M. suis in pigs was significantly higher in summer (65.3%; 95% CI: 61.0%, 69.5%) and autumn (65.0%; 95% CI: 59.0%, 70.6%) compared to spring (30.1%; 95% CI: 26.0%, 34.4%) and winter (36.4%; 95% CI: 31.4%, 41.5%). Farm-level risk factors were identified by multivariable logistic regression analysis. The associated factors retained in the final multivariable logistic regression model were drug treatment, presence of mosquitoes and flies, and frequency of disinfection. Drug treatment (OR=0.24; 95% CI: 0.07, 0.88; P=0.031) and frequency of disinfection (OR=0.23; 95% CI: 0.06, 0.90; P=0.035) were protective factors, and the presence of mosquitoes and flies (OR=5.994; 95% CI: 1.56, 23.00; P=0.009) was a risk factor for M. suis infection on farms. The results of the present study provide the first insight into the impact of associated determinants on M. suis infection in central China.

Mycoplasma suis infection results endothelial cell damage and activation: new insight into the cell tropism and pathogenicity of hemotrophic mycoplasma

Hemotrophic mycoplasmas (HM) are highly specialized red blood cell parasites that cause infectious anemia in a variety of mammals, including humans. To date, no in vitro cultivation systems for HM have been available, resulting in relatively little information about the pathogenesis of HM infection. In pigs, Mycoplasma suis-induced infectious anemia is associated with hemorrhagic diathesis, and coagulation dysfunction. However, intravasal coagulation and subsequent consumption coagulopathy can only partly explain the sequence of events leading to hemorrhagic diathesis manifesting as cyanosis, petechial bleeding, and ecchymosis, and to disseminated coagulation. The involvement of endothelial activation and damage in M. suis-associated pathogenesis was investigated using light and electron microscopy, immunohistochemistry, and cell sorting. M. suis interacted directly with endothelial cells in vitro and in vivo. Endothelial activation, widespread endothelial damage, and adherence of red blood cells to the endothelium were evident in M. suis-infected pigs. These alterations of the endothelium were accompanied by hemorrhage, intravascular coagulation, vascular occlusion, and massive morphological changes within the parenchyma. M. suis biofilm-like microcolonies formed on the surface of endothelial cells, and may represent a putative persistence mechanism of M. suis. In vitro analysis demonstrated that M. suis interacted with the endothelial cytoskeletal protein actin, and induced actin condensation and activation of endothelial cells, as determined by the up-regulation of ICAM, PECAM, E-selectin, and P-selectin. These findings demonstrate an additional cell tropism of HM for endothelial cells and suggest that M. suis interferes with the protective function of the endothelium, resulting in hemorrhagic diathesis.

Use of MSG1 protein in a novel blocking ELISA for the detection of Mycoplasma suis infection

A blocking ELISA based on the monoclonal antibody (MAb) 1A7 was developed to detect antibodies against Mycoplasma suis. The MAb was produced by immunising BALB/c mice with recombinant MSG1 protein (rMSG1) from M. suis expressed in E. coli. Following identification by Western blotting, the MAb was purified and labelled with horseradish peroxidase. The parameters of the ELISA were optimised, and the cut-off value determined as 36.35% by analysing the percentage inhibition of M. suis negative serum. The sensitivity and specificity of the ELISA were 92% and 100%, respectively. In repeatability tests, the intra- and inter-batch variation coefficients were <10%. The results suggest this blocking ELISA is specific, sensitive and reproducible, and will be a valuable tool in the serodiagnosis of M. suis infection in pigs.

Insights into the gene expression profile of uncultivable hemotrophic Mycoplasma suis during acute infection, obtained using proteome analysis

Hemotrophic mycoplasmas, bacteria without cell walls whose niche is the erythrocytes of their hosts, have never been cultivated in vitro. Therefore, knowledge of their pathogenesis is fundamental. Mycoplasma suis infects pigs, causing either acute fatal hemolytic anemia or chronic low-grade anemia, growth retardation, and immune suppression. Recently, the complete genomes of two hemotrophic mycoplasma species, M. suis and M. haemofelis, were sequenced, offering new strategies for the analysis of their pathogenesis. In this study we implemented a proteomic approach to identify M. suis proteins during acute infection by using tandem mass spectrometry. Twenty-two percent of the predicted proteins encoded in M. suis strain KI_3806 were identified. These included nearly all encoded proteins of glycolysis and nucleotide metabolism. The proteins for lipid metabolism, however, were underrepresented. A high proportion of the detected proteins are involved in information storage and processing (72.6%). In addition, several proteins of different functionalities, i.e., posttranslational modification, membrane genesis, signal transduction, intracellular trafficking, inorganic ion transport, and defense mechanisms, were identified. In its reduced genome, M. suis harbors 65.3% (strain Illinois) and 65.9% (strain KI_3806) of the genes encode hypothetical proteins. Of these, only 6.3% were identified at the proteome level. All proteins identified in this study are present in both M. suis strains and are encoded in more highly conserved regions of the genome sequence. In conclusion, our proteome approach is a further step toward the elucidation of the pathogenesis and life cycle of M. suis as well as the establishment of an in vitro cultivation system.

Role of GapC in the pathogenesis of Staphylococcus aureus

Staphylococcus aureus is recognized worldwide as a major pathogen causing clinical or subclinical intramammary infections in lactating cows, sheep and goats. S. aureus produces a wide arsenal of cell surface and extracellular proteins involved in virulence. Among these are two conserved proteins with glyceraldehyde-3-phosphate dehydrogenase (GAPDH) activity named glyceraldehyde-3-phosphate dehydrogenase-B (GapB) and -C (GapC). In this study, we used the S. aureus wild type strain RN6390 and its isogenic gapC mutant H330 in in vitro and in vivo studies and determined that the S. aureus GapC protein plays a role on adherence to and internalization into bovine mammary epithelial (MAC-T) cells. In addition, we found that S. aureus H330 did not caused mastitis after an experimental infection of ovine mammary glands. Together, these results show that GapC is important in the pathogenesis of S. aureus mastitis.

The surface-localised α-enolase of Mycoplasma suis is an adhesion protein

Mycoplasma suis belongs to the haemotrophic mycoplasmas which colonise red blood cells of a wide range of vertebrates. Adhesion to red blood cells is the crucial step in the unique lifecycle of M. suis. Due to the lack of a cultivation system, identification of adhesion structures has been difficult. So far, only one adhesion protein, i.e. MSG1 was identified. In order to determine further adhesion molecules of M. suis, we screened genomic M. suis libraries and performed Southern blot hybridisation analyses of genomic M. suis DNA. The α-enolase of M. suis was identified and analysed genetically and functionally. The encoding gene has 1623 bp in size. The deduced amino acid sequence showed an overall identity of 59.6-65.1% to α-enolases of other pathogenic mycoplasmas. The 540 aa M. suis α-enolase displays a size extension of about 90 aa in comparison to α-enolases of other mycoplasmas. Recombinant α-enolase expressed in Escherichia coli demonstrated immunogenicity in experimentally infected pigs. Immunoblot, confocal laser scanning microscopy and immune electron microscopy analysis using antibodies against recombinant α-enolase, indicate the membrane and surface localisation of native α-enolase in M. suis, though no typical signal sequences exist. Furthermore, we showed that recombinant α-enolase binds to porcine erythrocyte lysate in a dose-dependent manner. E. coli transformants which express α-enolase on their surface acquire the ability to adhere to porcine red blood cells. In conclusion, our observations indicate that α-enolase could be involved in the adhesion of M. suis to porcine red blood cells.

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.

Molecular characterization of the uncultivatable hemotropic bacterium Mycoplasma haemofelis

Mycoplasma haemofelis is a pathogenic feline hemoplasma. Despite its importance, little is known about its metabolic pathways or mechanism of pathogenicity due to it being uncultivatable. The recently sequenced M. haemofelis str. Langford 1 genome was analysed and compared to those of other available hemoplasma genomes.

Analysis showed that in hemoplasmas genes involved in carbohydrate metabolism are limited to enzymes of the glycolytic pathway, with glucose appearing to be the sole energy source. The majority of the pentose phosphate pathway enzymes that catalyze the de novo synthesis of ribonucleotides were absent, as were cell division protein FtsZ and chaperonins GroEL/ES. Uncharacterized protein paralogs containing putative surface expression motifs, comprised 62% of M. haemofelis and 19% of Mycoplasma suis genome coverage respectively, the majority of which were present in a small number of unstructured islands. Limited mass spectrometry and immunoblot data matched a number of characterized proteins and uncharacterized paralogs, confirming their expression and immunogenicity in vivo.

These data have allowed further characterization of these important pathogens, including their limited metabolic capabilities, which may contribute to their uncultivatable status. A number of immunogenic proteins, and a potential mechanism for host immune system evasion, have been identified.

Hemotrophic mycoplasmas induce programmed cell death in red blood cells

Hemotrophic mycoplasmas (HM) are uncultivable bacteria found on and in the red blood cells (RBCs). The main clinical sign of HM infections is the hemolytic anemia. However, anemia-inducing pathogenesis has not been totally clarified. In this work we used the splenectomized pig as animal model and Mycoplasma suis as a representative for hemotrophic mycoplasmas to study anemia pathogenesis. Eryptosis, i.e. programmed cell death of RBCs, is characterized by cell shrinkage, microvesiculation and phosphatidylserine (PS) exposure on the outer membrane. The eryptosis occurrence and its influence on anemia pathogenesis was observed over the time-course of M. suis infections in pigs using 3 M. suis isolates of differing virulence. All 3 isolates induced eryptosis, but with different characteristics. The occurrence of eryptosis could as well be confirmed in vitro: serum and plasma of an acutely ill pig induced PS exposure on erythrocytes drawn from healthy pigs. Since M. suis is able to induce eryptotic processes it is concluded that eryptosis is one anemia-inducing factor during M. suis infections and, therefore, plays a significant role in the pathogenesis of infectious anemia due to HM infection.

Protein chimeras containing the Mycoplasma bovis GAPDH protein and bovine host-defence peptides retain the properties of the individual components

Besides the well characterized role in glycolysis, glyceraldehyde-3-phosphate dehydrogenase (GAPDH) has been implicated in virulence of pathogenic micro-organisms and because of its cell surface location, it has been shown to act as an adhesin for colonization of tissue surfaces both for pathogenic and non-pathogenic normal microflora. These novel properties of GAPDH make this protein a target for studies in pathogenesis and a candidate for vaccine development against several diseases. Previously, we have isolated the GAPDH protein of Mycoplasma bovis and we are currently using this protein as a test antigen to develop a vaccine to protect feedlot animals from M. bovis-related diseases. As part of our vaccine studies, we are testing several novel immune modulators, some of which are host-defence peptides (HDP). HDP are small protein molecules that are part of the innate immune system of the host possess antimicrobial activities and can act as adjuvants. These novel compounds have been used as part of chimeric proteins composed of viral antigens fused to HDP and these chimeras were found to promote immune responses. The first step in the use of the M. bovis GAPDH protein and HDP as components of a vaccine was to construct M. bovis GAPDH-HDP chimeric proteins. The three M. bovis GAPDH-HDP chimeric proteins constructed here: GAPDH-BMAP28 (sGap-M), GAPDH-indolicidin (sGap-I), and GAPDH-TAP (Gap-T) retained properties associated with the individual components, namely GAPDH enzymatic and HDP antimicrobial activities.

Glyceraldehyde-3-phosphate dehydrogenase of the entomopathogenic fungus Metarhizium anisopliae: cell-surface localization and role in host adhesion

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is a classic glycolytic enzyme that plays important roles in various cellular processes. Here, we report the sequence and transcriptional analyses of a regulated gene (gpdh1) encoding GAPDH in the entomopathogenic fungus Metarhizium anisopliae, a well-characterized biocontrol agent of a wide range of arthropod pests. Transcript and protein analyses of the gpdh1 showed a carbohydrate-dependent expression pattern in response to different carbon sources. A demonstration that GAPDH is localized at the cell surface is presented, and assays with insect wings show that this protein has adhesion-like activity. These results imply that GAPDH adhesion to the wing surface is specific and may play a role in the binding of conidia to a host. Our observations indicate new roles for GAPDH both physiologically and during the entomopathogen-host interaction.

Invasion of bovine peripheral blood mononuclear cells and erythrocytes by Mycoplasma bovis

Mycoplasma bovis is a small, cell wall-less bacterium that contributes to a number of chronic inflammatory diseases in both dairy and feedlot cattle, including mastitis and bronchopneumonia. Numerous reports have implicated M. bovis in the activation of the immune system, while at the same time inhibiting immune cell proliferation. However, it is unknown whether the specific immune-cell population M. bovis is capable of attaching to and potentially invading. Here, we demonstrate that incubation of M. bovis Mb1 with bovine peripheral blood mononuclear cells (PBMC) resulted in a significant reduction in their proliferative responses while still remaining viable and capable of gamma interferon secretion. Furthermore, we show that M. bovis Mb1 can be found intracellularly (suggesting a role for either phagocytosis or attachment/invasion) in a number of select bovine PBMC populations (T cells, B cells, monocytes, γδ T cells, dendritic cells, NK cells, cytotoxic T cells, and T-helper cells), as well as red blood cells, albeit it at a significantly lower proportion. M. bovis Mb1 appeared to display three main patterns of intracellular staining: diffuse staining, an association with the intracellular side of the cell membrane, and punctate/vacuole-like staining. The invasion of circulating immune cells and erythrocytes could play an important role in disease pathogenesis by aiding the transport of M. bovis from the lungs to other sites.

Inorganic pyrophosphatase in uncultivable hemotrophic mycoplasmas: identification and properties of the enzyme from Mycoplasma suis

Background

Mycoplasma suis belongs to a group of highly specialized hemotrophic bacteria that attach to the surface of host erythrocytes. Hemotrophic mycoplasmas are uncultivable and the genomes are not sequenced so far. Therefore, there is a need for the clarification of essential metabolic pathways which could be crucial barriers for the establishment of an in vitro cultivation system for these veterinary significant bacteria.

Inorganic pyrophosphatases (PPase) are important enzymes that catalyze the hydrolysis of inorganic pyrophosphate PP_i to inorganic phosphate P_i. PPases are essential and ubiquitous metal-dependent enzymes providing a thermodynamic pull for many biosynthetic reactions. Here, we describe the identification, recombinant production and characterization of the soluble (s)PPase of Mycoplasma suis.

Results

Screening of genomic M. suis libraries was used to identify a gene encoding the M. suis inorganic pyrophosphatase (sPPase). The M. suis sPPase consists of 164 amino acids with a molecular mass of 20 kDa. The highest identity of 63.7% was found to the M. penetrans sPPase. The typical 13 active site residues as well as the cation binding signature could be also identified in the M. suis sPPase. The activity of the M. suis enzyme was strongly dependent on Mg²⁺ and significantly lower in the presence of Mn²⁺ and Zn²⁺. Addition of Ca²⁺ and EDTA inhibited the M. suis sPPase activity. These characteristics confirmed the affiliation of the M. suis PPase to family I soluble PPases. The highest activity was determined at pH 9.0. In M. suis the sPPase builds tetramers of 80 kDa which were detected by convalescent sera from experimentally M. suis infected pigs.

Conclusion

The identification and characterization of the sPPase of M. suis is an additional step towards the clarification of the metabolism of hemotrophic mycoplasmas and, thus, important for the establishment of an in vitro cultivation system. As an antigenic and conserved protein the M. suis sPPase could in future be further analyzed as a diagnostic antigen.

Antigen specificity of the humoral immune response to Mycoplasma haemofelis infection

The aim of the present study was to characterize the antigenic specificity of the humoral immune response made by cats infected with the feline hemoplasma, Mycoplasma haemofelis. A crude M. haemofelis antigen preparation was prepared from red blood cells (RBCs) collected from a cat at the time of a high level of bacteremia. Plasma samples were collected from six cats before and after experimental infection with M. haemofelis, with regular sampling being performed from 15 to 149 or 153 days postinfection (dpi). Preinfection RBC membrane ghosts were prepared from these six cats and used to identify erythrocyte proteins that may have contaminated the M. haemofelis antigen preparation. The M. haemofelis antigen preparation comprised 11 protein bands. The immunodominant bands on Western blotting with infected cat plasma had molecular masses of 78, 68, 60, 48, and 38 kDa. Most cats (n = 5) had plasma antibody that reacted with at least one band (always including the one of 68 kDa) at 15 dpi, and all cats were seroreactive by 29 dpi. The maximum number of antibodies from an individual animal specific for an antigen was identified in plasma collected from 57 to 99 dpi. Contamination of the M. haemofelis antigen preparation with RBC membrane proteins was observed. The contaminating RBC proteins had molecular masses of from 71 to 72 kDa (consistent with band 4.2) and 261 and 238 kDa (consistent with spectrin), and these were recognized by all plasma samples. A range of M. haemofelis antigens is recognized by cats infected experimentally with the organism. These represent possible targets for immunoassays, but care must be taken to prevent false-positive results due to host protein contamination.

Proteomic study of Mycoplasma suis using the gel-based shotgun strategy

Mycoplasma suis (M. suis) is an uncultivable pathogen that colonizes the surface of porcine erythrocytes. In the present study, gel-based LC-MS/MS was performed to analyze the proteomic composition of M. suis. We identified 191 proteins with two or more peptides and additional 217 putative proteins with one peptide hit by cross-species searching the Mollicutes protein databases. Resultant proteins were classified based on their molecular functions. The majority of enzymes involved in central carbon metabolic pathways and nucleotide biosynthesis were confirmed by searching the KEGG database. The present study is the first report addressing the proteome of M. suis. Results indicate that the energy source of M. suis might depend mainly on glycometabolism.

Identification of the binding domain of Streptococcus oralis glyceraldehyde-3-phosphate dehydrogenase for Porphyromonas gingivalis major fimbriae

Porphyromonas gingivalis forms communities with antecedent oral biofilm constituent streptococci. P. gingivalis major fimbriae bind to glyceraldehyde-3-phosphate dehydrogenase (GAPDH) present on the streptococcal surface, and this interaction plays an important role in P. gingivalis colonization. This study identified the binding domain of Streptococcus oralis GAPDH for P. gingivalis fimbriae. S. oralis recombinant GAPDH (rGAPDH) was digested with lysyl endopeptidase. Cleaved fragments of rGAPDH were applied to a reverse-phase high-pressure liquid chromatograph equipped with a C18 column. Each peak was collected; the binding activity toward P. gingivalis recombinant fimbrillin (rFimA) was analyzed with a biomolecular interaction analysis system. The fragment displaying the strongest binding activity was further digested with various proteinases, after which the binding activity of each fragment was measured. The amino acid sequence of each fragment was determined by direct sequencing, mass spectrometric analysis, and amino acid analysis. Amino acid residues 166 to 183 of S. oralis GAPDH exhibited the strongest binding activity toward rFimA; confocal laser scanning microscopy revealed that the synthetic peptide corresponding to amino acid residues 166 to 183 of S. oralis GAPDH (pep166-183, DNFGVVEGLMTTIHAYTG) inhibits S. oralis-P. gingivalis biofilm formation in a dose-dependent manner. Moreover, pep166-183 inhibited interbacterial biofilm formation by several oral streptococci and P. gingivalis strains with different types of FimA. These results indicate that the binding domain of S. oralis GAPDH for P. gingivalis fimbriae exists within the region encompassing amino acid residues 166 to 183 of GAPDH and that pep166-183 may be a potent inhibitor of P. gingivalis colonization in the oral cavity.

Vaccination with the Mycoplasma suis recombinant adhesion protein MSG1 elicits a strong immune response but fails to induce protection in pigs

Mycoplasma suis is the unculturable pathogen of porcine infectious anemia. The study was aimed to determine the immunogenicity and protective efficacy of MSG1, an immunodominant adhesin of M. suis as the first vaccine candidate against M. suis. The results demonstrated that recombinant MSG1 and Escherichia coli transformants expressing MSG1 (E. coli_MSG1) induced a strong humoral and cellular immunity against M. suis. The induced antibodies were found to be functionally active as confirmed by an in vitro adhesion inhibition assay. Both, IgG1 and IgG2 antibodies were induced, but E. coli_MSG1 immune response was characterized by a significantly higher IgG1 antibody production. Both vaccine candidates failed to protect against M. suis challenge. However, E. coli_MSG1 vaccination has a considerable effect on the severity of the disease as shown by higher post-challenge hemoglobin and hematocrit values in comparison to control groups. This indicated that a high IgG1 antibody titer is negatively connected with severity of M. suis-induced anemia. Furthermore, the induction of monospecific anti-MSG1 antibodies by both vaccine candidates clearly allows for the differentiation between infected and vaccinated animals (DIVA principle). Overall, the importance of MSG1 as potential vaccine candidate remains to be established. Future studies will evaluate the conditions (i.e. adjuvant, vaccination scheme, and application route) to optimize the effects of E. coli_MSG1 vaccines.

Haemotrophic mycoplasmas: recent advances in Mycoplasma suis

Haemotrophic mycoplasmas (haemoplasmas) are uncultivable, small epicellular, cell wall less, tetracycline-sensitive bacteria that attach to the surface of host erythrocytes. Today, haemotrophic mycoplasmas are found in a large number of animals, with Mycoplasma suis being the porcine pathogen. Haemoplasmas can cause infections which are clinically marked, either by an overt life-threatening haemolytic anaemia or a mild chronic anaemia, by illthrift, infertility, and immune suppression. The life cycle of haemoplasmas on the surface of nucleus-less red blood cells is unique for mycoplasma and therefore, it is evident that these haemotrophic pathogens must have features that allow them to colonise and replicate on red blood cells. However, the mechanisms of adhesion and replication of M. suis on erythrocytes, for instance, as well as the significance of metabolic interchanges between the agent and the target cells, are completely unknown to date. Far from having gained clear insight into the clinical significance of the haemoplasmas, our knowledge about the physiology, genetics, and host-pathogen interaction of this novel group of bacteria within the Mollicutes order is rather limited. This can be explained primarily by the unculturability of these bacteria. The enormous advances in molecular biology witnessed in recent years have had a major impact on several areas of biological sciences, i.e. the fields of modern medical bacteriology and infectious diseases. This review describes progress made in research of the pathobiology of M. suis these past few years.

Use of recombinant antigens to detect antibodies against Mycoplasma suis, with correlation of serological results to hematological findings

Porcine eperythrozoonosis is a disease with worldwide distribution caused by the unculturable hemotrophic bacterium Mycoplasma suis. Current serological testing utilizes crude M. suis antigens purified from the blood of experimentally infected pigs. These antigens show high variability and are restricted to specialized laboratories. We evaluated a novel serological assay based on two recombinant M. suis antigens (rMSG1 and rHspA1). Antigen specificity was proven by means of sera raised against nonhemotrophic mycoplasma and other relevant bacteria. Using experimental and convalescent-phase sera, rMSG1 and rHspA1 enzyme-linked immunosorbent assays (ELISAs) demonstrated sensitivities, specificities, and predictive values (94.0 to 100.0%) equal to or higher than those of the M. suis whole-cell ELISA. Field samples from 120 weaning piglets grouped by quantitative PCR results were used to evaluate the diagnostic capability of the new ELISA systems in comparison to that of the whole-cell ELISA. Assuming a 100.0% specificity of the PCR, the whole-cell ELISA, rHspA1 ELISA, and rMSG1 ELISA showed specificities of 84.8%, 83.8%, and 90.6% and sensitivities of 61.5%, 74.0% and 58.1%, respectively. Cohen's kappa coefficients comparing the recombinant ELISAs to the whole-cell ELISA indicate moderate to substantial agreement. The detection of anti-MSG1 and/or anti-HspA1 antibodies in pigs was significantly correlated with decreased hematocrit, erythrocyte numbers, and hemoglobin concentrations, indicating that a single seropositive result is connected with clinical and etiological significance. In conclusion, rMSG1 and rHspA1 are sensitive and specific serological and infection markers which are for the first time used independently of animal experiments. They are especially fit to be used in routine diagnosis, pathogenesis studies, and large-scale epidemiological investigations.

First LightCycler real-time PCR assay for the quantitative detection of Mycoplasma suis in clinical samples

Mycoplasma suis cannot be cultivated in vitro. Therefore, PCR-based methods are irreplaceable for the diagnosis of M. suis infections especially when clinical symptoms are not evident. Currently, no easy and reliable method allowing the quantitative detection of M. suis is available. This report describes the development of a quantitative LightCycler PCR assay based on the msg1 gene of M. suis (LC MSG1 PCR). No PCR signals were obtained with closely related haemotrophic and non-haemotrophic mycoplasmas, with other bacteria, and with M. suis-free blood and tissue arguing for a high analytical specificity. Test sensitivity was found to be 100%, and test specificity 96.7%. To test the diagnostic suitability of the LC MSG1 PCR, 25 pigs with clinical porcine eperythrozoonosis and 25 healthy pigs were investigated. All ill pigs revealed a positive real-time PCR result whereas only one healthy pig was detected to be M. suis-infected. M. suis was quantitatively detected in 19 blood specimens of 100 sows from Switzerland and in 17 of 160 post-weaning piglets from Germany. In conclusion, this new LC MSG1 PCR assay represents a powerful tool for the improvement of the current M. suis diagnosis and for prevalence and pathogenesis studies.