Antigenic and genetic characterization of lipoprotein LppQ from Mycoplasma mycoides subsp. mycoides SC

Host cell interactions of novel antigenic membrane proteins of Mycoplasma agalactiae

Background

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

Results

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

Conclusions

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

Supplementary Information

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

Contagious Bovine Pleuropneumonia: Challenges and Prospects Regarding Diagnosis and Control Strategies in Africa

Contagious bovine pleuropneumonia (CBPP) is an infectious and contagious respiratory disease of cattle, caused by Mycoplasma mycoides subsp. mycoides (Mmm). In this review, basic epidemiological features of CBPP, complicated by existing different strains of Mycoplasmas with similar biochemical characteristics, with preference to Sub-Saharan Africa are discussed. Many sub-Saharan African countries are challenged by variable gaps that include diagnostic tools and control strategies. Science-based issues on diagnostic procedures, vaccination, treatment, and other control strategies are discussed. Participatory epidemiology (PE), a diagnostic technique used in the identification and solving of animal health problems in rural communities, was also discussed. PE application, in conjunction with conventional diagnostic tools, will improve CBPP identification in pastoral rural communities and promote control of the disease in Africa. Furthermore, adequate CBPP control can be achieved through stronger political commitments from governments by prioritizing the disease among major diseases of high economic importance to the livestock industry for surveillance and control. Investment in CBPP control in endemic African countries will assure food security, livelihoods and the general well-being of people, and international trade.

Baseline analysis of Mycoplasma mycoides subsp. mycoides antigens as targets for a DIVA assay for use with a subunit vaccine for contagious bovine pleuropneumonia

BACKGROUND

Mycoplasma mycoides subsp. mycoides (Mmm) is the causative agent of contagious bovine pleuropneumonia in cattle. A prototype subunit vaccine is being developed, however, there is currently no diagnostic test that can differentiate between infected cattle and those vaccinated with the prototype subunit vaccine. This study characterized Mmm proteins to identify potential antigens for use in differentiating infected from vaccinated animals.

RESULTS

Ten Mmm antigens expressed as recombinant proteins were tested in an indirect ELISA using experimental sera from control groups, infected, and vaccinated animals. Data were imported into R software for analysis and drawing of the box and scatter plots while Cohen's Kappa assessed the level of agreement between the Mmm antigens. Two vaccine antigens (MSC_0499 and MSC_0776) were superior in detecting antibodies in sera of animals vaccinated with the subunit vaccines while two non-vaccine antigens (MSC_0636 and LppB) detected antibodies in sera of infected animals showing all clinical stages of the disease. Sensitivity and specificity of above 87.5% were achieved when the MSC_0499 and MSC_0636 antigens were tested on sera from vaccinated and infected animals.

CONCLUSIONS

The MSC_0499 and MSC_0776 antigens were the most promising for detecting vaccinated animals, while MSC_0636 and LppB were the best targets to identify infected animals. Further testing of sera from vaccinated and infected animals collected at different time intervals in the field should help establish how useful a diagnostic test based on a cocktail of these proteins would be.

Development of a Novel Cocktail Enzyme-Linked Immunosorbent Assay and a Field-Applicable Lateral-Flow Rapid Test for Diagnosis of Contagious Bovine Pleuropneumonia

Contagious bovine pleuropneumonia (CBPP) is a severe respiratory disease that is widespread in sub-Saharan Africa. It is caused by Mycoplasma mycoides subsp. mycoides, a bacterium belonging to the Mycoplasma mycoides cluster. In the absence of an efficient CBPP vaccine, improved and easy-to-use diagnostic assays for recurrent testing combined with isolation and treatment of positive animals represent an option for CBPP control in Africa. Here we describe the comprehensive screening of 17 immunogenic Mycoplasma mycoides subsp. mycoides proteins using well-characterized bovine sera for the development of a novel cocktail enzyme-linked immunosorbent assay (ELISA) for laboratory use. Two recombinant Mycoplasma immunogens, MSC_0136 and MSC_0636, were used to set up a standardized cocktail ELISA protocol. According to the results from more than 100 serum samples tested, the sensitivity and specificity of the novel cocktail ELISA were 85.6% and 96.4%, respectively, with an overall diagnostic accuracy comparable to that of the Office International des Epizooties (OIE)-prescribed serological assays. In addition, we provide a proof of principle for a field-applicable, easy-to-use commercially produced prototype lateral-flow test for rapid (<30-min) diagnosis of CBPP.

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.

Changes in pathogenicity and immunogenicity of Mycoplasma mycoides subsp. mycoides strains revealed by comparative genomics analysis

Mycoplasma mycoides subsp. mycoides is the causative agent of contagious bovine pleuropneumonia. A pathogenic strain BEN-1 was isolated from bovine lung and underwent continuous passages in rabbits for 468 generations. During this process, the strain's strong virulence became weak and, gradually, it lost the ability to confer protective immunity in cattle but developed virulence in rabbits. In order to gain insight into the mechanisms behind the reduction in virulence and the loss of immunogenicity, we sequenced five representative strains of the BEN series, including the original strain (BEN-1), the strain generation that first acquired virulence in rabbits (BEN-50), the two vaccine strain generations (BEN-181 and BEN-326), and the strain generation showing the greatest loss of immunogenicity (BEN-468). The gene mutation rate in the four different propagation stages varied greatly, and over half of variations observed in each generation were removed during the propagation process. However, the variation maintained in the BEN-468 generation might contribute to its changes in virulence and immunogenicity. We thus identified 18 genes associated with host adaptation, six genes contributing to virulence in cattle, and 35 genes participating in conferring immunity in cattle. These findings might help us optimize the vaccine to obtain more effective immunization results.

Vaccination of cattle with the N terminus of LppQ of Mycoplasma mycoides subsp. mycoides results in type III immune complex disease upon experimental infection

Contagious bovine pleuropneumonia (CBPP) is a serious respiratory disease of cattle caused by Mycoplasma mycoides subsp. mycoides. Current vaccines against CBPP induce short-lived immunity and can cause severe postvaccine reactions. Previous studies have identified the N terminus of the transmembrane lipoprotein Q (LppQ-N') of M. mycoides subsp. mycoides as the major antigen and a possible virulence factor. We therefore immunized cattle with purified recombinant LppQ-N' formulated in Freund's adjuvant and challenged them with M. mycoides subsp. mycoides. Vaccinated animals showed a strong seroconversion to LppQ, but they exhibited significantly enhanced postchallenge glomerulonephritis compared to the placebo group (P = 0.021). Glomerulonephritis was characterized by features that suggested the development of antigen-antibody immune complexes. Clinical signs and gross pathological scores did not significantly differ between vaccinated and placebo groups. These findings reveal for the first time the pathogenesis of enhanced disease as a result of antibodies against LppQ during challenge and also argue against inclusion of LppQ-N' in a future subunit vaccine for CBPP.

Serological prevalence of contagious bovine pleuropneumonia in agro-pastoral areas of Nigeria

BACKGROUND

Contagious bovine pleuropneumonia (CBPP), an infection of cattle caused by the small colony biotype of Mycoplasma mycoides subspecies mycoides (MmmSC), is a significant constraint to improved pastoral cattle productivity in sub-Saharan Africa. This cross-sectional study was aimed to estimate serological prevalence of CBPP and identify risk factors for herd sero-positivity within agro-pastoral areas of Nigeria.

RESULTS

The herd level prevalence of CBPP was 54.7% (95% confidence interval (CI) = 47.7-62.0), and proportion of animals with detectable MmmSC monoclonal antibody was 30.2% (95% CI = 26.3-34.4). Herds were more likely to be sero-positive if they were potentially exposed to recent CBPP outbreaks (odds ratio (OR) = 4.9, 95% CI = 2.4-10.1) or of larger sizes (OR = 3.0, 95% CI = 1.2-7.5). Herds vaccinated against the disease had lower odds of being sero-positive (OR = 0.12, 95% CI = 0.02-0.6) than unvaccinated herds.

CONCLUSIONS

CBPP is endemic to agro-pastoral areas, and it is doubtful if the current control strategies are making real impact in reducing production losses. Although eradication is more likely to be achieved through regional approaches, enhanced vaccination coverage supported with targeted surveillance and a trace back system based on cattle trade and movement records will sustain effective control of the disease in the Nigerian cattle population.

An adenoviral vector expressing lipoprotein A, a major antigen of Mycoplasma mycoides subspecies mycoides, elicits robust immune responses in mice

Contagious bovine pleuropneumonia (CBPP), caused by Mycoplasma mycoides subsp. mycoides small colony type (MmmSC), is a devastating respiratory disease of cattle. In sub-Saharan Africa, where CBPP is enzootic, live attenuated vaccines are deployed but afford only short-lived protection. In cattle, recovery from experimental MmmSC infection has been associated with the presence of CD4(+) T lymphocytes that secrete interferon gamma in response to MmmSC, and in particular to the lipoprotein A (LppA) antigen. In an effort to develop a better vaccine against CBPP, a viral vector (Ad5-LppA) that expressed LppA was generated from human adenovirus type 5. The LppA-specific immune responses elicited by the Ad5-LppA vector were evaluated in mice, and compared to those elicited by recombinant LppA formulated with a potent adjuvant. Notably, a single administration of Ad5-LppA, but not recombinant protein, sufficed to elicit a robust LppA-specific humoral response. After a booster administration, both vector and recombinant protein elicited strong LppA-specific humoral and cell-mediated responses. Ex vivo stimulation of splenocytes induced extensive proliferation of CD4(+) T cells for mice immunized with vector or protein, and secretion of T helper 1-associated and proinflammatory cytokines for mice immunized with Ad5-LppA. Our study - by demonstrating the potential of a viral-vectored prototypic vaccine to elicit prompt and robust immune responses against a major antigen of MmmSC - represents a first step in developing a recombinant vaccine against CBPP.

Specific evolution of F1-like ATPases in mycoplasmas

F(1)F(0) ATPases have been identified in most bacteria, including mycoplasmas which have very small genomes associated with a host-dependent lifestyle. In addition to the typical operon of eight genes encoding genuine F(1)F(0) ATPase (Type 1), we identified related clusters of seven genes in many mycoplasma species. Four of the encoded proteins have predicted structures similar to the α, β, γ and ε subunits of F(1) ATPases and could form an F(1)-like ATPase. The other three proteins display no similarity to any other known proteins. Two of these proteins are probably located in the membrane, as they have three and twelve predicted transmembrane helices. Phylogenomic studies identified two types of F(1)-like ATPase clusters, Type 2 and Type 3, characterized by a rapid evolution of sequences with the conservation of structural features. Clusters encoding Type 2 and Type 3 ATPases were assumed to originate from the Hominis group of mycoplasmas. We suggest that Type 3 ATPase clusters may spread to other phylogenetic groups by horizontal gene transfer between mycoplasmas in the same host, based on phylogeny and genomic context. Functional analyses in the ruminant pathogen Mycoplasma mycoides subsp. mycoides showed that the Type 3 cluster genes were organized into an operon. Proteomic analyses demonstrated that the seven encoded proteins were produced during growth in axenic media. Mutagenesis and complementation studies demonstrated an association of the Type 3 cluster with a major ATPase activity of membrane fractions. Thus, despite their tendency toward genome reduction, mycoplasmas have evolved and exchanged specific F(1)-like ATPases with no known equivalent in other bacteria. We propose a model, in which the F(1)-like structure is associated with a hypothetical X(0) sector located in the membrane of mycoplasma cells.

Assessment of a novel multiplex real-time PCR assay for the detection of the CBPP agent Mycoplasma mycoides subsp. mycoides SC through experimental infection in cattle

Background

Mycoplasma mycoides subsp. mycoides SC is the pathogenic agent of contagious bovine pleuropneumonia (CBPP), the most important disease of cattle in Africa causing significant economic losses. The re-emergence of CBPP in Europe in the 1980s and 1990s illustrates that it is still a threat also to countries that have successfully eradicated the disease in the past. Nowadays, probe-based real-time PCR techniques are among the most advanced tools for a reliable identification and a sensitive detection of many pathogens, but only few protocols have been published so far for CBPP diagnosis. Therefore we developed a novel TaqMan^®-based real-time PCR assay comprising the amplification of two independent targets (MSC_0136 and MSC_1046) and an internal exogenous amplification control in a multiplex reaction and evaluated its diagnostic performance with clinical samples.

Results

The assays detected 49 MmmSC strains from diverse temporal and geographical origin, but did not amplify DNA from 82 isolates of 20 non-target species confirming a specificity of 100%. The detection limit was determined to be 10 fg DNA per reaction for the MSC_0136 assay and 100 fg per reaction for the MSC_1046 assay corresponding to 8 and 80 genome equivalents, respectively. The diagnostic performance of the assay was evaluated with clinical samples from 19 experimentally infected cattle and from 20 cattle without CBPP and compared to those of cultivation and a conventional PCR protocol. The two rt-PCR tests proved to be the most sensitive methods and identified all 19 infected animals. The different sample types used were not equally suitable for MmmSC detection. While 94.7% of lung samples from the infected cohort were positively tested in the MSC_0136 assay, only 81% of pulmonal lymph nodes, 31% of mediastinal lymph nodes and 25% of pleural fluid samples gave a positive result.

Conclusions

The developed multiplex rt-PCR assay is recommended as an efficient tool for rapid confirmation of a presumptive CBPP diagnosis in a well-equipped laboratory environment.

A minor role of CD4+ T lymphocytes in the control of a primary infection of cattle with Mycoplasma mycoides subsp. mycoides

Contagious bovine pleuropneumonia (CBPP), caused by Mycoplasma mycoides subsp. mycoides, is an important livestock disease in Africa. The current control measures rely on a vaccine with limited efficacy and occasional severe side effects. Knowledge of the protective arms of immunity involved in this disease will be beneficial for the development of an improved vaccine. In previous studies on cattle infected with M. mycoides subsp. mycoides, a correlation was detected between the levels of mycoplasma-specific IFN-γ-secreting CD4⁺ T lymphocytes and reduced clinical signs. However, no cause and effect has been established, and the role of such cells and of protective responses acquired during a primary infection is not known.

We investigated the role of CD4⁺ T lymphocytes in CBPP by comparing disease patterns and post mortem findings between CD4⁺ T cell depleted and non-depleted cattle. The depletion was carried out using several injections of BoCD4 specific murine monoclonal antibody on day 6 after experimental endotracheal infection with the strain Afadé. All cattle were monitored clinically daily and sacrificed 28-30 days post-infection. Statistically significant but small differences were observed in the mortality rate between the depleted and non-depleted animals. However, no differences in clinical parameters (fever, signs of respiratory distress) and pathological lesions were observed, despite elimination of CD4⁺ T cells for more than a week. The slightly higher mortality in the depleted group suggests a minor role of CD4⁺ T cells in control of CBPP.

Comparison of complement fixation test, competitive ELISA and LppQ ELISA with post-mortem findings in the diagnosis of contagious bovine pleuropneumonia (CBPP)

The complement fixation test (CFT), the c-ELISA and an indirect LppQ ELISA were compared to post-mortem (PM) inspection for the diagnosis of contagious bovine pleuropneumonia (CBPP). Sera from 797 cattle in the CBPP affected area of Kazungula, Zambia and 202 sera from Lusaka, Zambia, a CBPP-free area were used. The clinical history of CBPP was recorded and all the cattle from Kazungula were slaughtered and PM inspections conducted. The prevalence of CBPP in Kazungula was 67.5% (95%CI 67.2%, 70.8%), 52.6% (95%CI 49.2%, 56.2%), 59.0% (95%CI 55.5%, 62.4%) and 44.4% (95%CI 41.0%, 47.9%) using PM inspection, CFT, c-ELISA and LppQ ELISA, respectively. Three of the 202 negative control animals tested positive on the c-ELISA although they were from a known CBPP negative zone. In this study, the c-ELISA was more sensitive in detecting cattle with lesions in the chronic stage than any other test whilst the CFT detected more during the onset stage. No single serological test could detect all stages of CBPP infection, therefore the use of more than one test is advised.

A versatile palindromic amphipathic repeat coding sequence horizontally distributed among diverse bacterial and eucaryotic microbes

Background

Intragenic tandem repeats occur throughout all domains of life and impart functional and structural variability to diverse translation products. Repeat proteins confer distinctive surface phenotypes to many unicellular organisms, including those with minimal genomes such as the wall-less bacterial monoderms, Mollicutes. One such repeat pattern in this clade is distributed in a manner suggesting its exchange by horizontal gene transfer (HGT). Expanding genome sequence databases reveal the pattern in a widening range of bacteria, and recently among eucaryotic microbes. We examined the genomic flux and consequences of the motif by determining its distribution, predicted structural features and association with membrane-targeted proteins.

Results

Using a refined hidden Markov model, we document a 25-residue protein sequence motif tandemly arrayed in variable-number repeats in ORFs lacking assigned functions. It appears sporadically in unicellular microbes from disparate bacterial and eucaryotic clades, representing diverse lifestyles and ecological niches that include host parasitic, marine and extreme environments. Tracts of the repeats predict a malleable configuration of recurring domains, with conserved hydrophobic residues forming an amphipathic secondary structure in which hydrophilic residues endow extensive sequence variation. Many ORFs with these domains also have membrane-targeting sequences that predict assorted topologies; others may comprise reservoirs of sequence variants. We demonstrate expressed variants among surface lipoproteins that distinguish closely related animal pathogens belonging to a subgroup of the Mollicutes. DNA sequences encoding the tandem domains display dyad symmetry. Moreover, in some taxa the domains occur in ORFs selectively associated with mobile elements. These features, a punctate phylogenetic distribution, and different patterns of dispersal in genomes of related taxa, suggest that the repeat may be disseminated by HGT and intra-genomic shuffling.

Conclusions

We describe novel features of PARCELs (Palindromic Amphipathic Repeat Coding ELements), a set of widely distributed repeat protein domains and coding sequences that were likely acquired through HGT by diverse unicellular microbes, further mobilized and diversified within genomes, and co-opted for expression in the membrane proteome of some taxa. Disseminated by multiple gene-centric vehicles, ORFs harboring these elements enhance accessory gene pools as part of the "mobilome" connecting genomes of various clades, in taxa sharing common niches.

Detection of Mycoplasma mycoides subsp. mycoides SC in bronchoalveolar lavage fluids of cows based on a TaqMan real-time PCR discriminating wild type strains from an lppQ(-) mutant vaccine strain used for DIVA-strategies

Contagious bovine pleuropneumonia (CBPP) is the most serious cattle disease in Africa, caused by Mycoplasma mycoides subsp. mycoides small-colony type (SC). CBPP control strategies currently rely on vaccination with a vaccine based on live attenuated strains of the organism. Recently, an lppQ(-) mutant of the existing vaccine strain T1/44 has been developed (Janis et al., 2008). This T1lppQ(-) mutant strain is devoid of lipoprotein LppQ, a potential virulence attribute of M. mycoides subsp. mycoides SC. It is designated as a potential live DIVA (Differentiating Infected from Vaccinated Animals) vaccine strain allowing both serological and etiological differentiation. The present paper reports on the validation of a control strategy for CBPP in cattle, whereby a TaqMan real-time PCR based on the lppQ gene has been developed for the direct detection of M. mycoides subsp. mycoides SC in ex vivo bronchoalveolar lavage fluids of cows and for the discrimination of wild type strains from the lppQ(-) mutant vaccine strain.

Protein-specific analysis of humoral immune responses in a clinical trial for vaccines against contagious bovine pleuropneumonia

Specific humoral immune responses in a clinical trial on cattle for vaccines against contagious bovine pleuropneumonia (CBPP) were investigated. The trial included a subunit vaccine consisting of five recombinant putative variable surface proteins of the infectious agent Mycoplasma mycoides subsp. mycoides small colony type (M. mycoides SC) compared to the currently approved attenuated vaccine strain T1/44 and untreated controls. Humoral immune responses to 65 individual recombinant surface proteins of M. mycoides SC were monitored by a recently developed bead-based array assay. Responses to the subunit vaccine components were found to be weak. Animals vaccinated with this vaccine were not protected and had CBPP lesions similar to those of the untreated controls. In correlating protein-specific humoral responses to T1/44-induced immunity, five proteins associated with a protective immune response were identified by statistical evaluation, namely, MSC_1046 (LppQ), MSC_0271, MSC_0136, MSC_0079, and MSC_0431. These five proteins may be important candidates in the development of a novel subunit vaccine against CBPP.

Multiplex screening of surface proteins from Mycoplasma mycoides subsp. mycoides small colony for an antigen cocktail enzyme-linked immunosorbent assay

A recombinant antigen cocktail enzyme-linked immunosorbent assay (ELISA) for diagnosis of contagious bovine pleuropneumonia (CBPP) was developed after careful selection of antigens among one-third of the surface proteome proteins of the infectious agent Mycoplasma mycoides subsp. mycoides small colony (M. mycoides SC). First, a miniaturized and parallelized assay system employing antigen suspension bead array technology was used to screen 97 bovine sera for humoral immune responses toward 61 recombinant surface proteins from M. mycoides SC. Statistical analysis of the data resulted in selection of eight proteins that showed strong serologic responses in CBPP-affected sera and minimal reactivity in negative control sera, with P values of <10(-6). Only minor cross-reactivity to hyperimmune sera against other mycoplasmas was observed. When applied in an ELISA, the cocktail of eight recombinant antigens allowed a fivefold signal separation between 24 CBPP-affected and 23 CBPP-free sera from different geographical origins. No false-positive results and only two false-negative results were obtained. In conclusion, the selected recombinant mycoplasma antigens qualified as highly specific markers for CBPP and could be employed in both a suspension bead array platform and a cocktail ELISA setting. This set of proteins and technologies therefore offers a powerful combination to drive and further improve serological assays toward reliable, simple, and cost-effective diagnosis of CBPP.

Recombinant surface proteomics as a tool to analyze humoral immune responses in bovines infected by Mycoplasma mycoides subsp. mycoides small colony type

A systematic approach to characterize the surface proteome of Mycoplasma mycoides subspecies mycoides small colony type (M. mycoides SC), the causative agent of contagious bovine pleuropneumonia (CBPP) in cattle, is presented. Humoral immune responses in 242 CBPP-affected cattle and controls were monitored against one-third of the surface proteins of M. mycoides SC in a high throughput magnetic bead-based assay. Initially, 64 surface proteins were selected from the genome sequence of M. mycoides SC and expressed as recombinant proteins in Escherichia coli. Binding of antibodies to each individual protein could then be analyzed simultaneously in minute sample volumes with the Luminex suspension array technology. The assay was optimized on Namibian CBPP-positive sera and Swedish negative controls to allow detection and 20-fold mean signal separation between CBPP-positive and -negative sera. Signals were proven to be protein-specific by inhibition experiments, and results agreed with Western blot experiments. The potential of the assay to monitor IgG, IgM, and IgA responses over time was shown in a proof-of-concept study with 116 sera from eight animals in a CBPP vaccine study. In conclusion, a toolbox with recombinant proteins and a flexible suspension array assay that allows multiplex analysis of humoral immune responses to M. mycoides SC has been created.

Analysis of the immunoproteome of Mycoplasma mycoides subsp. mycoides small colony type reveals immunogenic homologues to other known virulence traits in related Mycoplasma species

Contagious bovine pleuropneumonia (CBPP) caused by Mycoplasma mycoides subsp. mycoides small colony type (MmmSC) has been eradicated in the developed world, but it is still present in many countries of sub-Saharan Africa. After initially successful control measures in the 1960s it has been spreading due to a lack of money, fragmentation of veterinary services, uncontrolled cattle movement, insufficient vaccine efficacy and sensitivity of current diagnostic tests. In this study we used two-dimensional polyacrylamide gel electrophoresis followed by immunoblot with sera from MmmSC-infected animals and MALDI-ToF mass spectrometry to identify novel immunogenic proteins as candidate molecules for improved diagnostics and vaccines. We identified 24 immunogens recognized by pooled sera from experimentally infected cattle. Furthermore, a serum from an animal with acute clinical disease as well as severe pathomorphological lesions recognized 13 additional immunogens indicating variation in the antibody responses to CBPP amongst cattle. Most immunogens showed compelling similarity to protein/gene sequences in the two ruminant pathogens M. capricolum subsp. capricolum and M. mycoides subsp. mycoides large colony type both belonging to the mycoides cluster. Three of these proteins, namely glycerol-3-phosphate oxidase, adenylosuccinate synthase, and glyceraldehyde-3-phosphate dehydrogenase, had no compelling homologue in the other distantly related bovine pathogen M. agalactiae. In addition, translation elongation factor Tu, heat shock protein 70, pyruvate dehydrogenase, and FKBP-type peptidyl-prolyl isomerase, which have been found to mediate adhesion to host tissue in other mycoplasmas were shown to be expressed and recognized by sera. These proteins have potential for the development of improved diagnostic tests and possibly vaccines.

Comparative analysis of four lipoproteins from Mycoplasma mycoides subsp. mycoides Small Colony identifies LppA as a major T-cell antigen

Control of contagious bovine pleuropneumonia (CBPP), caused by Mycoplasma mycoides subsp. mycoides Small Colony (MmmSC), remains an important goal in Africa. Subunit vaccines triggering B and T-cell responses could represent a promising approach. To this aim, the T-cell immunogenicity of four MmmSC lipoproteins (LppA, LppB, LppC and LppQ), present in African strains and able to elicit humoral response, was evaluated. In vitro assays revealed that only LppA was recognized by lymph node lymphocytes taken from three cattle, 3 weeks after MmmSC exposure. Maintenance of the LppA-specific response, relying on CD4 T-cells and IFN gamma production, was then demonstrated 1 year after infection. LppA is thus an important target for the CD4 T-cells generated early after MmmSC infection and persisting in the lymph nodes of recovered cattle. Its role as a protective antigen and ability to in vivo trigger both arms of the host immune response remain to be evaluated.

Vaccines for Mycoplasma diseases in animals and man

Vaccines for important mycoplasma diseases, including contagious bovine and caprine pleuropneumonia, have been used for centuries, consisting mainly of infected tissue or fluids which are inoculated into sites at which the risk of severe infection is slight, such as the tail and bridge of the nose. Surprisingly, little progress has been made in developing safe, defined and protective alternatives, the vaccines today still consisting of mildly attenuated strains serially passaged in eggs or in culture. Ill-defined temperature-sensitive mutants are widely used for mycoplasmoses in poultry despite uncertainty about their mode of protection. Inactivated vaccines for enzootic pneumonia appear to have improved pig health worldwide, but disease reduction has been generally modest. Ironically, attempts to develop subunit preparations have often led to exacerbation of disease, particularly in human atypical pneumonia. Promising results have been seen in DNA vaccine technology, which has been applied to the development of mycoplasma vaccines for porcine enzootic pneumonia, but field trials still seem a long way off. No commercial vaccines exist for Mycoplasma bovis, despite evidence that this is a major cause of calf pneumonia, mastitis and arthritis.

Unmarked insertional mutagenesis in the bovine pathogen Mycoplasma mycoides subsp. mycoides SC: characterization of a lppQ mutant

Mycoplasma mycoides subspecies mycoides small colony (SC) is the aetiologic agent of contagious bovine pleuropneumonia (CBPP), a respiratory disease causing important losses in cattle production. The publication of the genome sequence of M. mycoides subsp. mycoides SC should facilitate the identification of putative virulence factors. However, real progress in the study of molecular mechanisms of pathogenicity also requires efficient molecular tools for gene inactivation. In the present study, we have developed a transposon-based approach for the random mutagenesis of M. mycoides subsp. mycoides SC. A PCR-based screening assay enabled the characterization of several mutants with knockouts of genes potentially involved in pathogenicity. The initial transposon was further improved by combining it with the transposon gammadelta TnpR/res recombination system to allow the production of unmarked mutations. Using this approach, we isolated a mutant free of antibiotic-resistance genes, in which the gene encoding the main lipoprotein LppQ was disrupted. The mutant was found to express only residual amounts of the truncated N-terminal end of LppQ. This approach opens the way to study virulence factors and pathogen-host interactions of M. mycoides subsp. mycoides SC and to develop new, genetically defined vaccine strains.

Expression and immunogenicity of six putative variable surface proteins in Mycoplasma mycoides subsp. mycoides SC

Variable surface protein Vmm and five Vmm-type proteins from Mycoplasma mycoides subsp. mycoides SC were analysed to determine whether these proteins are expressed in vivo in animals affected by contagious bovine pleuropneumonia (CBPP) and in vitro. Recombinant versions of these proteins were constructed and expressed in Escherichia coli after mutation of the TGA Trp codons to TGG. These proteins were then analysed by dot and Western blotting with sera from CBPP-affected cattle. Furthermore, affinity-purified polyclonal antibodies to the recombinant proteins were used in Western and colony blotting to look for expression of the putative Vmm-type proteins in cultured M. mycoides SC. This study demonstrates that immunoglobulins in CBPP sera recognize all putative Vmm-type proteins tested, indicating that these proteins or their homologues are expressed by mycoplasmas during natural infections. Vmm and one of the putative Vmm-type proteins showed variable expression in vitro.

Domain analysis of lipoprotein LppQ in Mycoplasma mycoides subsp. mycoides SC

The lipoprotein LppQ is the most prominent antigen of Mycoplasma mycoides subsp. mycoides small colony type (SC) during infection of cattle. This pathogen causes contagious bovine pleuropneumonia (CBPP), a devastating disease of considerable socio-economic importance in many countries worldwide. The dominant antigenicity and high specificity for M. mycoides subsp. mycoides SC of lipoprotein LppQ have been exploited for serological diagnosis and for epidemiological investigations of CBPP. Scanning electron microscopy and immunogold labelling were used to provide ultrastructural evidence that LppQ is located to the cell membrane at the outer surface of M. mycoides subsp. mycoides SC. The selectivity and specificity of this method were demonstrated through discriminating localization of extracellular (i.e., in the zone of contact with host cells) vs. integral membrane domains of LppQ. Thus, our findings support the suggestion that the accessible N-terminal domain of LppQ is surface exposed and such surface localization may be implicated in the pathogenesis of CBPP.

Molecular mechanisms of pathogenicity of Mycoplasma mycoides subsp. mycoides SC

Mycoplasma mycoides subsp. mycoides SC, the aetiological agent of contagious bovine pleuropneumonia (CBPP), is considered the most pathogenic of the Mycoplasma species. Its virulence is probably the result of a coordinated action of various components of an antigenically and functionally dynamic surface architecture. The different virulence attributes allow the pathogen to evade the host's immune defence, adhere tightly to the host cell surface, persist and disseminate in the host causing mycoplasmaemia, efficiently import energetically valuable nutrients present in the environment, and release and simultaneously translocate toxic metabolic pathway products to the host cell where they cause cytotoxic effects that are known to induce inflammatory processes and disease. This strategy enables the mycoplasma to exploit the minimal genetic information in its small genome, not only to fulfil the basic functions for its replication but also to damage host cells in intimate proximity thereby acquiring the necessary bio-molecules, such as amino acids and nucleic acid precursors, for its own biosynthesis and survival.

Beta-D-glucoside utilization by Mycoplasma mycoides subsp. mycoides SC: possible involvement in the control of cytotoxicity towards bovine lung cells

Background

Contagious bovine pleuropneumonia (CBPP) caused by Mycoplasma mycoides subsp. mycoides small-colony type (SC) is among the most serious threats for livestock producers in Africa. Glycerol metabolism-associated H₂O₂ production seems to play a crucial role in virulence of this mycoplasma. A wide number of attenuated strains of M. mycoides subsp. mycoides SC are currently used in Africa as live vaccines. Glycerol metabolism is not affected in these vaccine strains and therefore it does not seem to be the determinant of their attenuation. A non-synonymous single nucleotide polymorphism (SNP) in the bgl gene coding for the 6-phospho-β-glucosidase (Bgl) has been described recently. The SNP differentiates virulent African strains isolated from outbreaks with severe CBPP, which express the Bgl isoform Val₂₀₄, from strains to be considered less virulent isolated from CBPP outbreaks with low mortality and vaccine strains, which express the Bgl isoform Ala₂₀₄.

Results

Strains of M. mycoides subsp. mycoides SC considered virulent and possessing the Bgl isoform Val₂₀₄, but not strains with the Bgl isoform Ala₂₀₄, do trigger elevated levels of damage to embryonic bovine lung (EBL) cells upon incubation with the disaccharides (i.e., β-D-glucosides) sucrose and lactose. However, strains expressing the Bgl isoform Val₂₀₄ show a lower hydrolysing activity on the chromogenic substrate p-nitrophenyl-β-D-glucopyranoside (pNPbG) when compared to strains that possess the Bgl isoform Ala₂₀₄. Defective activity of Bgl in M. mycoides subsp. mycoides SC does not lead to H₂O₂ production. Rather, the viability during addition of β-D-glucosides in medium-free buffers is higher for strains harbouring the Bgl isoform Val₂₀₄ than for those with the isoform Ala₂₀₄.

Conclusion

Our results indicate that the studied SNP in the bgl gene is one possible cause of the difference in bacterial virulence among strains of M. mycoides subsp. mycoides SC. Bgl does not act as a direct virulence factor, but strains possessing the Bgl isoform Val₂₀₄ with low hydrolysing activity are more prone to survive in environments that contain high levels of β-D-glucosides, thus contributing in some extent to mycoplasmaemia.

A metabolic enzyme as a primary virulence factor of Mycoplasma mycoides subsp. mycoides small colony

During evolution, pathogenic bacteria have developed complex interactions with their hosts. This has frequently involved the acquisition of virulence factors on pathogenicity islands, plasmids, transposons, or prophages, allowing them to colonize, survive, and replicate within the host. In contrast, Mycoplasma species, the smallest self-replicating organisms, have regressively evolved from gram-positive bacteria by reduction of the genome to a minimal size, with the consequence that they have economized their genetic resources. Hence, pathogenic Mycoplasma species lack typical primary virulence factors such as toxins, cytolysins, and invasins. Consequently, little is known how pathogenic Mycoplasma species cause host cell damage, inflammation, and disease. Here we identify a novel primary virulence determinant in Mycoplasma mycoides subsp. mycoides Small Colony (SC), which causes host cell injury. This virulence factor, released in significant amounts in the presence of glycerol in the growth medium, consists of toxic by-products such as H2O2 formed by l-alpha-glycerophosphate oxidase (GlpO), a membrane-located enzyme that is involved in the metabolism of glycerol. When embryonic calf nasal epithelial cells are infected with M. mycoides subsp. mycoides SC in the presence of physiological amounts of glycerol, H2O2 is released inside the cells prior to cell death. This process can be inhibited with monospecific anti-GlpO antibodies.

Genetic and antigenic characterisation of elongation factor Tu from Mycoplasma mycoides subsp. mycoides SC

Specific serodiagnosis of contagious bovine pleuropneumonia (CBPP) is hampered by the low antibody titers against Mycoplasma mycoides subsp. mycoides small-colony type (MmmSC) antigens in calf serum due to persistent infections and by the existence of cross-reactions among the members of the mycoides cluster. In order to identify potential diagnostic antigens, we have constructed a genomic library from MmmSC which was screened with antibodies from naturally-infected animals. Using this strategy, a genome fragment has been isolated and characterised. The complete nucleotide sequence of this fragment revealed the presence of several open reading frames, including that of translation elongation factor Tu (EF-Tu), whose product was responsible of the positive reaction observed when expressed in E. coli. The organisation of this MmmSC genome region differed from that of other Mycoplasma species whose complete genome sequences are known, but was similar, by PCR amplification analysis of genomic DNA, to other members of the mycoides cluster, such as Mycoplasma capricolum subsp. capricolum (Mcc). Nevertheless, the MmmSC and Mcc amplicons could be distinguished by digestion with restriction enzymes AseI or HindIII, strategy that could be used as a tool for differential diagnosis of infections caused by members of the mycoides cluster. The full recombinant EF-Tu was produced in E. coli, after correction of an unusual tryptophan codon by site-directed mutagenesis, and used to investigate anti-EF-Tu circulating antibodies in bovine sera.

Serodiagnosis and monitoring of contagious bovine pleuropneumonia (CBPP) with an indirect ELISA based on the specific lipoprotein LppQ of Mycoplasma mycoides subsp. mycoides SC

An indirect ELISA, based on the specific and strongly antigenic recombinant peptide of the N'-terminal half of the lipoprotein LppQ from Mycoplasma mycoides subsp. mycoides small colony type (SC) was developed for the detection of antibodies to M. mycoides subsp. mycoides SC. It was evaluated for its suitability for serodiagnosis and monitoring of contagious bovine pleuropneumonia (CBPP). The recombinant peptide containing poly-histidine residue tails was expressed in Escherichia coli and subsequently purified by Ni(2+) chelate affinity chromatography to be used as antigen to coat microtiter ELISA plates. The specificity of the antigen was tested against rabbit hyperimmune sera directed against related Mycoplasmas of the M. mycoides cluster and with sera from cattle that were either free of CBPP, but suffered from other mycoplasmal infections such as M. bovis, or showed cross-reactions in the complement fixation test. The sensitivity of the ELISA was assessed with sera from artificially infected animals and with sera from cattle originating from areas where CBPP was endemic at the time of blood sampling. The study revealed that the ELISA was both specific and sensitive for CBPP positive bovine sera and was shown also to be robust to harsh climatic conditions.