Mechanisms and factors involved in Mycoplasma bovis adhesion to host cells

LppA is a novel plasminogen receptor of Mycoplasma bovis that contributes to adhesion by binding the host extracellular matrix and Annexin A2

Mycoplasma bovis is responsible for various inflammatory diseases in cattle. The prevention and control of M. bovis are complicated by the absence of effective vaccines and the emergence of multidrug-resistant strains, resulting in substantial economic losses worldwide in the cattle industry. Lipoproteins, vital components of the Mycoplasmas cell membrane, are deemed potent antigens for eliciting immune responses in the host upon infection. However, the functions of lipoproteins in M. bovis remain underexplored due to their low sequence similarity with those of other bacteria and the scarcity of genetic manipulation tools for M. bovis. In this study, the lipoprotein LppA was identified in all examined M. bovis strains. Utilizing immunoelectron microscopy and Western blotting, it was observed that LppA localizes to the surface membrane. Recombinant LppA demonstrated dose-dependent adherence to the membrane of embryonic bovine lung (EBL) cells, and this adhesion was inhibited by anti-LppA serum. In vitro binding assays confirmed LppA's ability to associate with fibronectin, collagen IV, laminin, vitronectin, plasminogen, and tPA, thereby facilitating the conversion of plasminogen to plasmin. Moreover, LppA was found to bind and enhance the accumulation of Annexin A2 (ANXA2) on the cell membrane. Disrupting LppA in M. bovis significantly diminished the bacterium's capacity to adhere to EBL cells, underscoring LppA's function as a bacterial adhesin. In conclusion, LppA emerges as a novel adhesion protein that interacts with multiple host extracellular matrix proteins and ANXA2, playing a crucial role in M. bovis's adherence to host cells and dissemination. These insights substantially deepen our comprehension of the molecular pathogenesis of M. bovis.

A genome-wide transposon mutagenesis screening identifies LppB as a key factor associated with Mycoplasma bovis colonization and invasion into host cells

Mycoplasma spp., the smallest self-replicating and genome-reduced organisms, have raised a great concern in both the medical and veterinary fields due to their pathogenicity. The molecular determinants of these wall-less bacterium efficiently use their limited genes to ensure successful infection of the host remain unclear. In the present study, we used the ruminant pathogen Mycoplasma bovis as a model to identify the key factors for colonization and invasion into host cells. We constructed a nonredundant fluorescent transposon mutant library of M. bovis using a modified transposon plasmid, and identified 34 novel adhesion-related genes based on a high-throughput screening approach. Among them, the ΔLppB mutant exhibited the most apparent decrease in adhesion to embryonic bovine lung (EBL) cells. The surface-localized lipoprotein LppB, which is highly conserved in Mycoplasma species, was then confirmed as a key factor for M. bovis adhesion with great immunogenicity. LppB interacted with various components (fibronectin, vitronectin, collagen IV, and laminin) of host extracellular matrix (ECM) and promoted plasminogen activation through tPA to degrade ECM. The 439-502 amino acid region of LppB is a critical domain, and F465 and Y493 are important residues for the plasminogen activation activity. We further revealed LppB as a key factor facilitating internalization through clathrin- and lipid raft-mediated endocytosis, which helps the Mycoplasma invade the host cells. Our study indicates that LppB plays a key role in Mycoplasma infection and is a potential new therapeutic and vaccine target for Mycoplasma species.

Drug sensitivity and genome-wide analysis of two strains of Mycoplasma gallisepticum with different biofilm intensity

Mycoplasma gallisepticum (MG) is one of the major causative agents of chronic respiratory diseases in poultry. The biofilms of MG are highly correlated to its chronic infection. However data on genes involved in biofilm formation ability are still scarse. MG strains with distinct biofilm intensity were screened by crystal violet staining morphotyped and characterized for the drug sensitivity. Two MG strains NX-01 and NX-02 showed contrasted ability to biofilm formation. The biofilm formation ability of NX-01 strain was significantly higher than that of NX-02 strain (p < 0.01). The drug sensitivity test showed that the stronger the ability of MG stain to form biofilms, the weaker its sensitivity to 17 antibiotic drugs. Moreover, putative key genes related to biofilm formation were screened by genome-wide analysis. A total of 13 genes and proteins related to biofilm formation, including ManB, oppA, oppD, PDH, eno, RelA, msbA, deoA, gapA, rpoS, Adhesin P1 precursor, S-adenosine methionine synthetase, and methionyl tRNA synthetase were identified. There were five major discrepancies between the two isolated MG strains and the five NCBI-published MG strains. These findings provide potential targets for inhibiting the formation of biofilm of MG, and lay a foundation for treating chronic infection.

Mycoplasma Bovis adhesins and their target proteins

Bovine mycoplasmosis is an important infectious disease of cattle caused by Mycoplasma bovis (M. bovis) which poses a serious threat to the breeding industry. Adhesin is involved in the initial process of M. bovis colonization, which is closely related to the infection, cell invasion, immune escape and virulence of this pathogenic microorganism. For the reason that M. bovis lacks a cell wall, its adhesin is predominantly located on the surface of the cell membrane. The adhesins of M. bovis are usually identified by adhesion and adhesion inhibition analysis, and more than 10 adhesins have been identified so far. These adhesins primarily bind to plasminogen, fibronectin, heparin and amyloid precursor-like protein-2 of host cells. This review aims to concisely summarize the current knowledge regarding the adhesins of M. bovis and their target proteins of the host cell. Additionally, the biological characteristics of the adhesin will be briefly analyzed.

Biofilm formation and its impact on environmental survival and antibiotic resistance of Mycoplasma anserisalpingitidis strains

Several Mycoplasma species can form biofilm, facilitating their survival in the environment, and shielding them from therapeutic agents. The aim of this study was to examine the biofilm-forming ability and its potential effects on environmental survival and antibiotic resistance in Mycoplasma anserisalpingitidis, the clinically and economically most important waterfowl Mycoplasma species. The biofilm-forming ability of 32 M. anserisalpingitidis strains was examined by crystal violet assay. Biofilms and planktonic cultures of the selected strains were exposed to a temperature of 50 °C (20 and 30 min), to desiccation at room temperature (16 and 24 h), or to various concentrations of eight different antibiotics. Crystal violet staining revealed great diversity in the biofilm-forming ability of the 32 tested M. anserisalpingitidis strains, with positive staining in more than half of them. Biofilms were found to be more resistant to heat and desiccation than planktonic cultures, while no correlation was shown between biofilm formation and antibiotic susceptibility. Our results indicate that M. anserisalpingitidis biofilms may contribute to the persistence of the organisms in the environment, which should be taken into account for proper management. Antibiotic susceptibility was not affected by biofilm formation; however, it is important to note that correlations were examined only in vitro.

Mycoplasmas bovis P48 induces apoptosis in EBL cells via an endoplasmic reticulum stress-dependent signaling pathway

Mycoplasma bovis (M. bovis) is a small bacterium that lacks a cell wall. M. bovis infection can result in chronic pneumonia and polyarthritis syndrome (CPPS), otitis media, conjunctivitis, and meningitis in feedlot cattle and mastitis in dairy cattle. To gain more understanding of the mechanism of M. bovis and host interaction, this study focused on P48, an important membrane protein involved in M. bovis adhesion, proliferation and virulence. In this study, exogenous P48 protein was introduced to explore its function in embryonic bovine lung (EBL) cells by recombinant vector and protein purification. We found that M. bovis infection inhibited EBL cells growth and enhanced apoptosis. Both intracellular and extracellular P48 protein treatment also induce apoptosis. Moreover, P48 activates endoplasmic reticulum (ER) stress response via increasing ER stress markers expression. To further explore the underlying mechanism, we performed inhibition experiments using ER stress inhibitor 4-PBA and specific siRNA interference against GRP78, and found that P48 protein modulated EBL cells apoptosis in an ER stress signaling-dependent manner. This study provided more data to further understand M. bovis infection mechanism and develop effective anti-mycoplasma strategy.

A Review of Ureaplasma diversum: A Representative of the Mollicute Class Associated With Reproductive and Respiratory Disorders in Cattle

The Mollicutes class encompasses wall-less microbes with a reduced genome. They may infect plants, insects, humans, and animals including those on farms and in livestock. Ureaplasma diversum is a mollicute associated with decreased reproduction mainly in the conception rate in cattle, as well as weight loss and decreased quality in milk production. Therefore, U. diversum infection contributes to important economic losses, mainly in large cattle-producing countries such as the United States, China, Brazil, and India. The characteristics of Mollicutes, virulence, and pathogenic variations make it difficult to control their infections. Genomic analysis, prevalence studies, and immunomodulation assays help better understand the pathogenesis of bovine ureaplasma. Here we present the main features of transmission, virulence, immune response, and pathogenesis of U. diversum in bovines.

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

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

Progresses on bacterial secretomes enlighten research on Mycoplasma secretome

Bacterial secretome is a comprehensive catalog of bacterial proteins that are released or secreted outside the cells. They offer a number of factors that possess several significant roles in virulence as well as cell to cell communication and hence play a core role in bacterial pathogenesis. Sometimes these proteins are bounded with membranes giving them the shape of vesicles called extracellular vesicles (EVs) or outer membrane vesicles (OMVs). Bacteria secrete these proteins via Sec and Tat pathways into the periplasm. Secreted proteins have found to be important as diagnostic markers as well as antigenic factors for the development of an effective candidate vaccine. Recently, the research in the field of secretomics is growing up and getting more interesting due to their direct involvement in the pathogenesis of the microorganisms leading to the infection. Many pathogenic bacteria have been studied for their secretome and the results illustrated novel antigens. This review highlights the secretome studies of different pathogenic bacteria in humans and animals, general secretion mechanisms, different approaches and challenges in the secretome of Mycoplasma sp.

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

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

Large-Scale Analysis of the Mycoplasma bovis Genome Identified Non-essential, Adhesion- and Virulence-Related Genes

Mycoplasma bovis is an important pathogen of cattle causing bovine mycoplasmosis. Clinical manifestations are numerous, but pneumonia, mastitis, and arthritis cases are mainly reported. Currently, no efficient vaccine is available and antibiotic treatments are not always satisfactory. The design of new, efficient prophylactic and therapeutic approaches requires a better understanding of the molecular mechanisms responsible for M. bovis pathogenicity. Random transposon mutagenesis has been widely used in Mycoplasma species to identify potential gene functions. Such an approach can also be used to screen genomes and search for essential and non-essential genes for growth. Here, we generated a random transposon mutant library of M. bovis strain JF4278 containing approximately 4000 independent insertion sites. We then coupled high-throughput screening of this mutant library to transposon sequencing and bioinformatic analysis to identify M. bovis non-essential, adhesion- and virulence-related genes. Three hundred and fifty-two genes of M. bovis were assigned as essential for growth in rich medium. Among the remaining non-essential genes, putative virulence-related factors were subsequently identified. The complete mutant library was screened for adhesion using primary bovine mammary gland epithelial cells. Data from this assay resulted in a list of conditional-essential genes with putative adhesion-related functions by identifying non-essential genes for growth that are essential for host cell-adhesion. By individually assessing the adhesion capacity of six selected mutants, two previously unknown factors and the adhesin TrmFO were associated with a reduced adhesion phenotype. Overall, our study (i) uncovers new, putative virulence-related genes; (ii) offers a list of putative adhesion-related factors; and (iii) provides valuable information for vaccine design and for exploring M. bovis biology, pathogenesis, and host-interaction.

Bovine Epithelial in vitro Infection Models for Mycoplasma bovis

Mycoplasma bovis causes bovine mycoplasmosis. The major clinical manifestations are pneumonia and mastitis. Recently an increase in the severity of mastitis cases was reported in Switzerland. At the molecular level, there is limited understanding of the mechanisms of pathogenicity of M. bovis. Host–pathogen interactions were primarily studied using primary bovine blood cells. Therefore, little is known about the impact of M. bovis on other cell types present in infected tissues. Clear in vitro phenotypes linked to the virulence of M. bovis strains or tissue predilection of specific M. bovis strains have not yet been described. We adapted bovine in vitro systems to investigate infection of epithelial cells with M. bovis using a cell line (MDBK: Madin-Darby bovine kidney cells) and two primary cells (PECT: bovine embryonic turbinate cells and bMec: bovine mammary gland epithelial cells). Two strains isolated before and after the emergence of severe mastitis cases were selected. Strain JF4278 isolated from a cow with mastitis and pneumonia in 2008 and strain L22/93 isolated in 1993 were used to assess the virulence of M. bovis genotypes toward epithelial cells with particular emphasis on mammary gland cells. Our findings indicate that M. bovis is able to adhere to and invade different epithelial cell types. Higher titers of JF4278 than L22/93 were observed in co-cultures with cells. The differences in titers reached between the two strains was more prominent for bMec cells than for MDBK and PECT cells. Moreover, M. bovis strain L22/93 induced apoptosis in MDBK cells and cytotoxicity in PECT cells but not in bMec cells. Dose-dependent variations in proliferation of primary epithelial cells were observed after M. bovis infection. Nevertheless, an indisputable phenotype that could be related to the increased virulence toward mammary gland cells is not obvious.

Fructose-1,6-bisphosphate aldolase of Mycoplasma bovis is a plasminogen-binding adhesin

Mycoplasma bovis is an extremely small cell wall-deficient pathogenic bacterium in the genus Mycoplasma that causes serious economic losses to the cattle industry worldwide. Fructose-1,6-bisphosphate aldolase (FBA), a key enzyme in the glycolytic pathway, is a multifunctional protein in several pathogenic bacterial species, but its role in M. bovis remains unknown. Herein, the FBA gene of the M. bovis was amplified by PCR, and subcloned into the prokaryotic expression vector pET28a (+) to generate the pET28a-FBA plasmid for recombinant expression in Escherichia coli Transetta. Expression of the 34 kDa recombinant rMbFBA protein was confirmed by electrophoresis, and enzymatic activity assays based on conversion of NADH to NAD+ revealed Km and Vmax values of 48 μM and 43.8 μmoL/L/min, respectively. Rabbit anti-rMbFBA and anti-M. bovis serum were generated by inoculation with rMbFBA and M. bovis, and antigenicity and immunofluorescence assay demonstrated that FBA is an immunogenic protein expressed on the cell membrane in M. bovis cells. Enzyme-linked immunosorbent assays revealed equal distribution of FBA in the cell membrane and cytoplasm. Complement-dependent mycoplasmacidal assays showed that rabbit anti-rMbFBA serum killed 44.1% of M. bovis cells in the presence of complement. Binding and ELISA assays demonstrated that rMbFBA binds native bovine plasminogen and in a dose-dependent manner. Fluorescent microscopy revealed that pre-treatment with antibodies against rMbFBA decreased the adhesion of M. bovis to embryonic bovine lung (EBL) cells. Furthermore, adherence inhibition assays revealed 34.4% inhibition of M. bovis infection of EBL cells following treatment with rabbit anti-rMbFBA serum, suggesting rMbFBA participates in bacterial adhesion to EBL cells.

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

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

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

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

Differential Immunoreactivity to Bovine Convalescent Serum Between Mycoplasma bovis Biofilms and Planktonic Cells Revealed by Comparative Immunoproteomic Analysis

Mycoplasma bovis is a major bovine pathogen that causes considerable economic losses in the cattle industry worldwide. Moreover, M. bovis biofilm can persist in the environment and its host. To date, M. bovis biofilm antigens recognized by bovine convalescent sera and their comparison with planktonic cells have not yet been explored. This study utilized an immunoproteomic approach using two-dimensional electrophoresis, immunoblotting using convalescent bovine serum, and subsequent matrix-assisted laser desorption/ionization time-of-flight tandem mass spectrometry (MALDI-TOF/TOF MS) to identify the immunoreactive proteins expressed in biofilm- and planktonic-grown M. bovis strain 08M. Results showed that M. bovis biofilms and planktonic cells demonstrate differential immunoreactivity to bovine convalescent serum for the first time. A total of 10 and 8 immunoreactive proteins were identified for biofilms and planktonic cells, respectively. To our knowledge, a total of 12 out of 15 had not been reported as immunoreactive proteins in M. bovis, and six were specific to M. bovis biofilms. Three proteins, namely, endoglucanase, thiol peroxidase, and one putative membrane protein, that is, mycoplasma immunogenic lipase A, were identified in planktonic cells and biofilms. Most of the identified proteins were cytoplasmic proteins that were mainly involved in transport and metabolism. Moreover, ATP binding, oxidoreductase activity, and GTP binding were their most representative molecular functions. DnaK and Tuf appeared to be the most interactive immunoreactive agent among the identified proteins. Furthermore, six proteins had potential as serodiagnostic antigens. These data will be helpful to improve our current understanding on the host response to M. bovis biofilms and planktonic cells, which may facilitate the development of novel molecular candidates of improved diagnostics and vaccines to prevent M. bovis infections.

Mycoplasma bovis co-infection with bovine viral diarrhea virus in bovine macrophages

Several studies suggest that synergisms between Mycoplasma bovis and other microorganisms might exacerbate disease outcome of bovine mycoplasmosis. Screening several bovine cell types to assess their potential use as in vitro infection models for M. bovis, it was observed that a widely used cell line of bovine macrophages (Bomac cells) is in fact persistently infected with bovine viral diarrhea virus (BVDV). The cell line was first cured of this virus allowing comparative studies between both cell lines. Subsequently, uptake and co-culture of two M. bovis strains of different clonal complexes with Bomac cells contaminated with BVDV and in BVDV-free Bomac cells were assessed. Additionally, cell viability, cytotoxicity and induction of apoptosis after infection with M. bovis were evaluated. No differences in the levels of uptake and growth in co-culture were observed between the two Bomac cell types and both M. bovis strains. Cytotoxicity was increased after infection of BVDV-free cells with one of the two strains, while apoptotic cell death was slightly induced by this strain in both cell lines. Overall, the presence or absence of BVDV in Bomac cells did not grossly change the parameters tested upon infection with M. bovis. Nevertheless, this cell model is very useful when studying viral co-infections with bacteria and could also be used for multiple co-infections. Considering the broad contamination of cell cultures with BVDV, careful screening for this virus should routinely be performed as its presence might be relevant depending on the molecular mechanisms being investigated.

Proteomics analysis and its role in elucidation of functionally significant proteins in Mycoplasma bovis

Mycoplasma bovis (M. bovis) is an emerging devastating cause of pneumonia in dairy and feedlot calves around the world, largely due to its increasing resistance to new generation effective antibiotics and lack of efficient vaccine. Failure of protective measures against M. bovis is mainly due to nonspecific targets. Most of the virulent factors of M. bovis and their underlying mechanisms are obscure to devise an effective control strategy. Full genome sequences of M. bovis strains basically provided a useful platform for the accurate identification of novel proteins and understanding their biological value using proteomics tools. Most of the previously documented proteins of M. bovis are involved in adhesion to host cells and are antigenic in nature. However, host immune response to some antigens proved to be non-protective. For the diagnosis of M. bovis infection, a serological assay based on whole cell proteins of M. bovis is commercially available but the specificity is likely to be improved by identifying and targeting the specific proteins. Many of the predicted proteins of M. bovis remain hypothetical, as their functions are yet to be confirmed experimentally. This review mainly focuses on the proteomics analysis of M. bovis and its role in identification of the virulence related factors and antigenic proteins of M. bovis. Future research directions have also been highlighted in this script for the application of important antigenic factors of M. bovis.

TrmFO, a Fibronectin-Binding Adhesin of Mycoplasma bovis

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

Mycoplasma bovis NADH oxidase functions as both a NADH oxidizing and O2 reducing enzyme and an adhesin

Mycoplasma bovis causes considerable economic losses in the cattle industry worldwide. In mycoplasmal infections, adhesion to the host cell is of the utmost importance. In this study, the amino acid sequence of NOX was predicted to have enzymatic domains. The nox gene was then cloned and expressed in Escherichia coli. The enzymatic activity of recombinant NOX (rNOX) was confirmed based on its capacity to oxidize NADH to NAD⁺ and reduce O₂ to H₂O₂. The adherence of rNOX to embryonic bovine lung (EBL) cells was confirmed with confocal laser scanning microscopy, enzyme-linked immunosorbent assay, and flow cytometry. Both preblocking EBL cells with purified rNOX and preneutralizing M. bovis with polyclonal antiserum to rNOX significantly reduced the adherence of M. bovis to EBL cells. Mycoplasma bovis^NOX–expressed a truncated NOX protein at a level 10-fold less than that of the wild type. The capacities of M. bovis^NOX– for cell adhesion and H₂O₂ production were also significantly reduced. The rNOX was further used to pan phage displaying lung cDNA library and fibronectin was determined to be potential ligand. In conclusion, M. bovis NOX functions as both an active NADH oxidase and adhesin, and is therefore a potential virulence factor.

Immunoproteomic identification of MbovP579, a promising diagnostic biomarker for serological detection of Mycoplasma bovis infection

A lack of knowledge regarding the antigenic properties of Mycoplasma bovis proteins prevents the effective control of bovine infections using immunological approaches. In this study, we detected and characterized a specific and sensitive M. bovis diagnostic biomarker. After M. bovis total proteins and membrane fractions were separated with two dimensional gel electrophoresis, proteins reacting with antiserawere detected using MALDI-TOF MS. Thirty-nine proteins were identified, 32 of which were previously unreported. Among them, immunoinformatics predicted eight antigens, encoded by Mbov_0106, 0116, 0126, 0212, 0275, 0579, 0739, and 0789, to have high immunological value. These genes were expressed in E. coli after mutagenesis of UGA to UGG using overlap extension PCR. A lipoprotein, MbovP579, encoded by a functionally unknown gene, was a sensitive and specific antigen for detection of antibodies in sera from both M. bovis-infected and vaccinated cattle. The specificity of MbovP579 was confirmed by its lack of cross-reactivity with other mycoplasmas, including Mycoplasma agalactiae. An iELISA based on rMbovP579 detected seroconversion 7 days post-infection (dpi). The ELISA had sensitivity of 90.2% (95% CI: 83.7%, 94.3%) and a specificity of 97.8% (95% CI: 88.7%, 99.6%) with clinical samples. Additional comparative studies showed that both diagnostic and analytic sensitivities of the ELISA were higher than those of a commercially available kit (p<0.01). We have thus detected and characterized the novel antigen, MbovP579, and established an rMbovP579-based ELISA as a highly sensitive and specific method for the early diagnosis of M. bovis infection.

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.

Invasion and persistence of Mycoplasma bovis in embryonic calf turbinate cells

Mycoplasma bovis is a wall-less bacterium causing bovine mycoplasmosis, a disease showing a broad range of clinical manifestations in cattle. It leads to enormous economic losses to the beef and dairy industries. Antibiotic treatments are not efficacious and currently no efficient vaccine is available. Moreover, mechanisms of pathogenicity of this bacterium are not clear, as few virulence attributes are known. Microscopic observations of necropsy material suggest the possibility of an intracellular stage of M. bovis. We used a combination of a gentamicin protection assay, a variety of chemical treatments to block mycoplasmas entry in eukaryotic cells, and fluorescence and transmission electron microscopy to investigate the intracellular life of M. bovis in calf turbinate cells. Our findings indicate that M. bovis invades and persists in primary embryonic calf turbinate cells. Moreover, M. bovis can multiply within these cells. The intracellular phase of M. bovis may represent a protective niche for this pathogen and contribute to its escape from the host’s immune defense as well as avoidance of antimicrobial agents.

Molecular cloning and characterization of a surface-localized adhesion protein in Mycoplasma bovis Hubei-1 strain

Mycoplasma bovis (M. bovis) is an important pathogen that causes various bovine diseases, such as mastitis in cows and pneumonia in calves. The surface proteins are generally thought to play a central role in the pathogenesis of this organism. We screened the entire genome of M. bovis Hubei-1 and discovered a gene named vpmaX that encodes the 25 kDa variable surface lipoprotein A (VpmaX). Sequence analysis revealed that VpmaX contains several repetitive units and a typical bacterial lipoprotein signal sequence. The vpmaX gene was cloned and expressed in E. coli to obtain recombinant VpmaX (rVpmaX). Western blot analysis using a rabbit antibody against rVpmaX demonstrated that VpmaX is a membrane protein. Immunostaining visualized via confocal laser scanning microscopy showed that rVpmaX was able to adhere to embryonic bovine lung cells (EBL), and this was also confirmed by a sandwich ELISA. In summary, a surface-localized adhesion protein was identified in M. bovis Hubei-1.

Chronic pneumonia in calves after experimental infection with Mycoplasma bovis strain 1067: characterization of lung pathology, persistence of variable surface protein antigens and local immune response

Background

Mycoplasma bovis is associated with pneumonia in calves characterized by the development of chronic caseonecrotic lesions with the agent persisting within the lesion. The purposes of this study were to characterize the morphology of lung lesions, examine the presence of M. bovis variable surface protein (Vsp) antigens and study the local immune responses in calves after infection with M. bovis strain 1067.

Methods

Lung tissue samples from eight calves euthanased three weeks after experimental infection with M. bovis were examined by bacteriology and pathology. Lung lesions were evaluated by immunohistochemical (IHC) staining for wide spectrum cytokeratin and for M. bovis Vsp antigens and pMB67 antigen. IHC identification and quantitative evaluation of CD4⁺ and CD8⁺ T lymphocytes and immunoglobulin (IgG1, IgG2, IgM, IgA)-containing plasma cells was performed. Additionally, expression of major histocompatibility complex class II (MHC class II) was studied by IHC.

Results

Suppurative pneumonic lesions were found in all calves. In two calves with caseonecrotic pneumonia, necrotic foci were surrounded by epithelial cells resembling bronchial or bronchiolar epithelium. In all calves, M. bovis Vsp antigens were constantly present in the cytoplasm of macrophages and were also present extracellularly at the periphery of necrotic foci. There was a considerable increase in numbers of IgG1- and IgG2-positive plasma cells among which IgG1-containing plasma cells clearly predominated. Statistical evaluation of the numbers of CD4⁺ and CD8⁺ T cells, however, did not reveal statistically significant differences between inoculated and control calves. In M. bovis infected calves, hyperplasia of bronchus-associated lymphoid tissue (BALT) was characterized by strong MHC class II expression of lymphoid cells, but only few of the macrophages demarcating the caseonecrotic foci were positive for MHC class II.

Conclusions

The results from this study show that infection of calves with M. bovis results in various lung lesions including caseonecrotic pneumonia originating from bronchioli and bronchi. There is long-term persistence of M. bovis as demonstrated by bacteriology and immunohistochemistry for M. bovis antigens, i.e. Vsp antigens and pMB67. The persistence of the pathogen and its ability to evade the specific immune response may in part result from local downregulation of antigen presenting mechanisms and an ineffective humoral immune response with prevalence of IgG1 antibodies that, compared to IgG2 antibodies, are poor opsonins.

Mycoplasma bovis pneumonia in cattle

Mycoplasma bovis is an important and emerging cause of respiratory disease and arthritis in feedlot cattle and young dairy and veal calves, and has a variety of other disease manifestations in cattle. M. bovis is certainly capable of causing acute respiratory disease in cattle, yet the attributable fraction has been difficult to estimate. In contrast, M. bovis is more accepted as a cause of chronic bronchopneumonia with caseous and perhaps coagulative necrosis, characterized by persistent infection that seems poorly responsive to many antibiotics. An understanding of the disease has been recently advanced by comparisons of natural and experimentally induced disease, development of molecular diagnostic tools, and understanding some aspects of virulence, yet uncertainties regarding protective immunity, the importance of genotypic diversity, mechanisms of virulence, and the role of co-pathogens have restricted our understanding of pathogenesis and our ability to effectively control the disease. This review critically considers the relationship between M. bovis infection and the various manifestations of the bovine respiratory disease complex, and addresses the pathogenesis, clinical and pathologic sequelae, laboratory diagnosis and control of disease resulting from M. bovis infection in the bovine respiratory tract.

Sialidase activity in Mycoplasma synoviae

Eleven strains of the avian pathogen Mycoplasma synoviae were evaluated for the presence of sialidase activity with the use of the fluorogenic substrate 2'-(4-methylumbelliferyl)-alpha-D-N-acetylneuraminic acid and the sialidase inhibitor 2-deoxy-2,3- didehydro-N-acetylneuraminic acid. The kinetics of in vitro growth in modified Frey medium were also assessed for each strain. Five strains had been isolated from clinically symptomatic chickens, and strains WVU 1853T and K3344 have been demonstrated to be capable of reproducing disease in specific-pathogen-free chickens. All strains exhibited sialidase activity, although the amount varied 65-fold among strains (P < 0.0001) from 1.3 x 10(-7) to 2.0 x 10(-9) activity units per colony-forming unit. Strains originally isolated from clinically symptomatic birds had more (P < 0.05) sialidase activity than strains from asymptomatic birds. Strain WVU1853T exhibited the most sialidase activity (P < 0.0001) and grew to the highest culture density (P < 0.0001) among strains, but across strains, the rank correlation of growth rate with sialidase activity was not significant. Negligible activity was detected in conditioned culture supernatant fluid. This is the first report of sialidase activity in pathogenic strains of M. synoviae, which suggests a potential enzymatic basis for virulence of the organism.

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.

Biofilm formation by mycoplasma species and its role in environmental persistence and survival

Although mycoplasmas possess a very limited genome, little is known about their virulence mechanisms and methods of persistence in the host. Examination of a wide range of mycoplasma species found considerable variation in their ability to form a biofilm. Mycoplasma putrefaciens, M. cottewii, M. yeatsii, M. agalactiae and M. bovis produced prolific biofilms. Conversely, the highly pathogenic mycoplasma and causative agent of contagious bovine pleuropneumonia, Mycoplasma mycoides subsp. mycoides SC, was unable to produce a biofilm. Biofilms were found to be considerably more resistant to stress, including heat and desiccation, than planktonic cells. A link between the biofilm phenotype and genotype as determined by molecular typing was found for M. bovis. Analysis of biofilms using fluorescent staining combined with confocal microscopy demonstrated that mycoplasma biofilms formed a highly differentiated structure with stacks and channels. Biofilm formation may indicate that mycoplasmas are capable of surviving in the environment.

Identification by two-dimensional electrophoresis of a new adhesin expressed by a low-passaged strain of Mycoplasma bovis

A significant decrease in adherence rates of Mycoplasma bovis to bovine bronchial epithelial (BBE) cells has been observed after passage of the organism in artificial medium. Analysis of the proteins expressed by M. bovis isolate 2610 by two-dimensional (2-D) electrophoresis demonstrated differences between the cells harvested after the 7th and 116th passage. Three silver-stained prominent spots observed in 2-D electrophoretic separation of protein extracts of the lower-passaged cells were considerably less strongly expressed in the sample from higher-passaged cells. These spots had a molecular mass of approximately 24 kDa and an isoelectric point of about 5. The mass spectrometry analysis of these trypsin-sensitive proteins led to their identification as a unique new member of the Vsps family of membrane-associated proteins. Serum from a mouse immunized with these proteins significantly reduced adherence of M. bovis to BBE cells. This result underlines the function of this new Vsp in adherence of M. bovis to host cells.

A 63 kDa VSP9B10A-like protein expressed in a C-8 Giardia duodenalis Mexican clone

BACKGROUND

It is well documented that Giardia duodenalis undergoes surface antigenic variation both in vivo and in vitro. Proteins involved have been characterized and referred to as VSP (variable surface protein).

METHODS

Two cloned cDNA inserts of 0.45 and 1.95 kb were obtained from G. duodenalis expression library and sequenced. Comparison sequence analyses were made against Genbank. PCR analysis was performed on G. duodenalis isolates to identify isolates bearing genes encoding such a peptide. Specific antiserum was prepared against 450-bp encoded peptide and tested by Western blot, immunofluorescence, and inhibition of adhesion of G. duodenalis to target cells.

RESULTS

We cloned and characterized a G. duodenalis 450-bp DNA fragment; its DNA sequence analysis revealed that this fragment displayed 99% identity with vsp9B10A gene. Predicted amino acid sequence for this fragment also had significant (99%) identity to VSP9B10A. A second 1.95-kb insert, which encompassed the 450-bp cDNA fragment, was also isolated; its DNA and amino acid sequence displayed 99.5% identity with vsp9B10A gene and 99.2% with the corresponding inferred protein, respectively. This inferred protein contained 24 Cys-X-X-Cys motifs and long ORF of 642 aminoacids. PCR analysis showed that DNA sequence encoding a fragment of this gene was present in P1, CIEA:0487:2-C-8 clone and in INP:180800-B2 G. duodenalis human isolates, while it was absent in sheep isolate of G. duodenalis INP:150593-J10.

CONCLUSIONS

Immunofluorescence analysis using antibodies raised against the peptide encoded by 450-bp fragment showed that expression of this epitope varies on trophozoite surface of the C-8 Mexican clone and is involved in parasite adhesion to target epithelial cells.

Adherence of Mycoplasma bovis to bovine bronchial epithelial cells

Mycoplasma bovis is responsible for considerable economic losses in cattle due to pneumonia, arthritis and mastitis. As the agent was shown to be capable of adhering to neutrophils and embryonic bovine lung (EBL) cells and invading the respiratory epithelium it is highly desirable to improve our understanding of cytadherence processes. Although several surface proteins likely to be directly involved in this initial stage of interaction between pathogen and host cells have been identified, these findings mainly referred to type strain PG45 adhering to the continuous EBL cell line. The present study provides new and complementary data about cytadherence of M. bovis based on adherence of various radiolabeled strains to a primary culture of bovine bronchial epithelial (BBE) cells using a standardized adherence assay. M. bovis was shown to adhere specifically to the primary culture of BBE cells. Inhibition of adherence was observed upon addition of monoclonal antibodies (MAbs), trypsin treatment of mycoplasmas, and competition with non-radiolabeled mycoplasma cells. Interestingly, three MAbs against proteins involved in adherence to EBL cells failed to inhibit significantly the adherence to BBE cells. On the other hand, significant reduction of adherence rates by MAbs 2A8 and 9F1 directed against epitopes of variable surface lipoproteins VspC and VspF, respectively, demonstrated the involvement of these proteins in adherence of M. bovis to primary culture of BBE cells.

Adherence to various host cell lines of Mycoplasma bovis strains differing in pathogenic and cultural features

Mycoplasma bovis is known to be responsible for pneumonia and arthritis in calves, as well as mastitis in dairy cows. Despite clear evidence of its pathogenic potential, little is known about mechanisms of cytadherence and the molecular factors involved. The purpose of this work was to compare adherence rates of M. bovis field strains to different host cell lines and study the effects of cloning and sub-culturing M. bovis strains on their adherence properties. Eighteen metabolically labeled M. bovis strains isolated from different pathological backgrounds were examined in adherence trials using four different host cell lines, i.e. embryonic bovine lung (EBL), embryonic bovine trachea (EBTr), Madin Darby bovine kidney (MDBK) and rabbit kidney (RK) cells. Although large interstrain variations in adherence rates (3.4-19.1%) were measured they could not be correlated to the pathological background (pneumonia, arthritis or mastitis). Adherence rates to the fibroblast cell line (EBTr) were significantly lower than those to the three epithelial cell lines (EBL, MDBK and RK). The only non-pathogenic strain (221/89) exhibited lower adherence rates than three isolates from clinical mastitis. Interestingly, adherence rates were significantly reduced after in vitro passaging. In contrast, no effect of single cloning of strains on adherence was observed. There was no general correlation between expression of variable surface proteins (Vsps) as monitored by immunoblotting and adherence rates, although alterations in Vsp expression profiles were seen as a consequence of passaging. As there is probably a large number of adhesins, variable and non-variable, on the surface of M. bovis cells the issue is very complex, and the most active components have yet to be identified.

Identification and functional mapping of the Mycoplasma fermentans P29 adhesin

Initial adherence interactions between mycoplasmas and mammalian cells are important for host colonization and may contribute to subsequent pathogenic processes. Despite significant progress toward understanding the role of specialized, complex tip structures in the adherence of some mycoplasmas, particularly those that infect humans, less is known about adhesins through which other mycoplasmas of this host bind to diverse cell types, even though simpler surface components are likely to be involved. We show by flow cytometric analysis that a soluble recombinant fusion protein (FP29), representing the abundant P29 surface lipoprotein of Mycoplasma fermentans, binds human HeLa cells and inhibits M. fermentans binding to these cells, in both a quantitative and a saturable manner, whereas analogous fusion proteins representing other mycoplasma surface proteins did not. Constructs representing nested N- or C-terminal truncations of FP29 allowed initial mapping of this specific adherence function to a central region of the P29 sequence containing a 36-amino-acid disulfide loop. A derivative of FP29 containing a mutation converting one participating Cys to Ser, precluding intrachain disulfide bond formation, retained full activity. Together these results suggest that the direct interaction of M. fermentans with a ligand on the HeLa cell surface involves a limited segment of the P29 surface lipoprotein and requires neither the disulfide bond nor the contribution of adjacent portions of the protein. Earlier results indicating phase-variable display of monoclonal antibody surface epitopes on P29, now recognized to be outside this ligand binding region, raise the possibility that variation of mycoplasma surface architecture might alter the presentation of the binding region and the adherence phenotype. Preliminary results further indicated that FP29 could inhibit binding to HeLa cells by Mycoplasma hominis, a distinct human mycoplasma species displaying the phase-variable adhesin Vaa, but not that by Mycoplasma capricolum, an organism infecting caprine species. This result raises the additional, testable possibility that a common host cell ligand for two human mycoplasma species may be recognized through structurally dissimilar adhesins that undergo phase variation by two distinct mechanisms, governing protein expression (Vaa) or surface masking (P29).

Mapping antigenic sites of an immunodominant surface lipoprotein of Mycoplasma agalactiae, AvgC, with the use of synthetic peptides

As a first step toward the design of an epitope vaccine to prevent contagious agalactia, the strongly immunogenic 55-kDa protein of Mycoplasma agalactiae was studied and found to correspond to the AvgC protein encoded by the avgC gene. The avg genes of M. agalactiae, which encode four variable surface lipoproteins, display a significant homology to the vsp (variable membrane surface lipoproteins) genes of the bovine pathogen Mycoplasma bovis at their promoter region as well as their N-terminus-encoding regions. Some members of the Vsp family are known to be involved in cytoadhesion to host cells. In order to localize immunogenic peptides in the AvgC antigen, the protein sequence was submitted to epitope prediction analysis, and five sets of overlapping peptides, corresponding to five selected regions, were synthesized by Spot synthesis. Reactive peptides were selected by immunobinding assay with sera from infected sheep. The three most immunogenic epitopes were shown to be surface exposed by immunoprecipitation assays, and one of these was specifically recognized by all tested sera. Our study indicates that selected epitopes of the AvgC lipoprotein may be used to develop a peptide-based vaccine which is effective against M. agalactiae infection.

Characterization of a multigene family undergoing high-frequency DNA rearrangements and coding for abundant variable surface proteins in Mycoplasma agalactiae

A family of abundant surface proteins (Vpmas [variable proteins of Mycoplasma agalactiae]) undergoing phase variation in M. agalactiae has been characterized using monoclonal antibodies and specific polyclonal sera. Two expressed members of 39 kDa (Vpma39) and 34 kDa (Vpma34), which varied in expression between clones of a lineage, shared a common amino-terminal sequence but were immunologically distinct. An amino-terminal oligonucleotide probe identified multiple vpma genes which were clustered within a 14-kb ClaI genomic fragment. Rearrangements were found to have occurred within the vpma locus between clones which correlated with changes in their Vpma phenotype. Two neighboring vpma genes were cloned and sequenced from one M. agalactiae clonal variant expressing Vpma39. The two genes, vpmaX and vpmaY, were orientated divergently and shared highly homologous 5' untranslated regions, 25-amino-acid (aa) lipoprotein leader sequences, and amino-terminal sequences. The vpmaY gene coded for 346 aa and 84% of the open reading frame, comprised of 1.5 units of a large repeat of 186 aa. Although the sequence for an entire second vpmaY repeat was present, it was prematurely terminated by insertion of two nucleotides. The vpmaX gene encoded 221 aa and possessed 102 aa of the 186-aa repeat of vpmaY. Many of the features in common between the vpma genes were also found to be shared by the vsp genes of M. bovis, which also undergo DNA rearrangements concomitant with phenotypic changes. Since M. bovis is the closest phylogenetic relative to M. agalactiae, the vpma and vsp gene families most probably represent homologous systems.

Epitope mapping of immunogenic and adhesive structures in repetitive domains of Mycoplasma bovis variable surface lipoproteins

The family of variable surface lipoproteins (Vsps) of the bovine pathogen Mycoplasma bovis includes some of the most immunogenic antigens of this microorganism. Vsps were shown to undergo high-frequency phase and size variations and to possess extensive reiterated coding sequences extending from the N-terminal end to the C-terminal end of the Vsp molecule. In the present study, mapping experiments were conducted to detect regions with immunogenicity and/or adhesion sites in repetitive domains of four Vsp antigens of M. bovis, VspA, VspB, VspE, and VspF. In enzyme-linked immunosorbent assay experiments, sera obtained from naturally infected cattle showed antibodies to different repeating peptide units of the Vsps, particularly to units R(A)1, R(A)2, R(A)4.1, R(B)2.1, R(E)1, and R(F)1, all of which were found to contain immunodominant epitopes of three to seven amino acids. Competitive adherence trials revealed that a number of oligopeptides derived from various repeating units of VspA, VspB, VspE, and VspF partially inhibited cytoadhesion of M. bovis PG45 to embryonic bovine lung cells. Consequently, putative adherence sites were identified in the same repeating units (R(A)1, R(A)2, R(A)4.1, R(B)2.1, R(E)1, and R(F)1) and in R(F)2. The positions and lengths of the antigenic determinants were mostly identical to those of adhesion-mediating sites in all short repeating units, whereas in the considerably longer R(F)1 unit (84 amino acid residues), there was only one case of identity among four immunogenic epitopes and six adherence sites. The identification of epitopes and adhesive structures in repetitive domains of Vsp molecules is consistent with the highly immunogenic nature observed for several members of the Vsp family and suggests a possible function for these Vsp molecules as complex adherence-mediating regions in pathogenesis.

Vsp antigens and vsp-related DNA sequences in field isolates of Mycoplasma bovis

The expression of the 1E5 epitope which is common to the three characterized variable lipoproteins VspA, VspB and VspC of Mycoplasma bovis type strain PG45 and the presence of vsp gene DNA sequences were assessed in field isolates randomly collected from cattle showing clinical manifestations due to M. bovis infection. Among 250 isolates tested, only four failed to react with mAb 1E5. Southern blot analysis of these four isolates and of 20 isolates expressing the 1E5 epitope were performed using synthetic oligonucleotide probes corresponding to a sequence located in the Vsp signal peptide coding region common to all known Vsp products or to selected regions of previously characterized vsp genes, vspA, vspE and vspF. The results demonstrate the presence of multiple vsp-related DNA sequences in all M. bovis field isolates tested and indicate that the vsp repertoire varies in size and composition among isolates.

Intraspecies polymorphism of vsp genes and expression profiles of variable surface protein antigens (Vsps) in field isolates of Mycoplasma bovis

To assess the extent of interstrain variation, 50 isolates of Mycoplasma (M.) bovis including the type strain PG45 were examined for the presence of a family of variable membrane surface lipoproteins (Vsps) and their genes. Southern hybridization using a genomic fragment carrying three distinct vsp genes (vspAEF) revealed a striking heterogeneity, with only 2/50 strains having identical banding patterns. Cluster analysis of the data showed that most isolates from interrelated herds (groups 1, 2 and 3) were combined in a cluster of 50% homology, while isolates from distinct geographical regions (groups 4, 5 and 6) were linked only at 18% homology. Vsp antigen expression was monitored by Western immunoblotting using four specific monoclonal antibodies (MAbs). Resembling the findings at the DNA level, interstrain variation of Vsp expression among groups 1-3 was less pronounced than among non-interrelated isolates from groups 4-6. Ten out of 50 strains did not hybridize with the vspAEF gene probe at high-stringency conditions, 8/50 failed to react with any of the Vsp-related MAbs, and 6/50 proved negative in both assays. Interestingly, most of these isolates produced hybridization signals at low stringency suggesting major distinctions in their vsp gene structure. The extensive evidence obtained on interstrain vsp gene polymorphism and variation in Vsp expression could provide a basis for a future understanding of the pathogenic potential of individual M. bovis strains.

Environmental factors influence P. aeruginosa binding to the wounded mouse cornea

PURPOSE

To determine whether environmental factors or bacterial viability affect the binding of two strains of P. aeruginosa to mouse cornea.

METHODS

Scarified corneas were placed in organ culture and inoculated with P. aeruginosa cell suspensions containing either ATCC 19660 or PAO1 bacterial strains classed as cytotoxic or invasive, respectively. Eyes were incubated in vitro for 1 h after bacterial application at different pH or temperature conditions or in PBS containing various divalent cations. The adhesion of heat-killed or formalin-fixed bacteria was tested similarly. Scanning electron microscopy (scanning EM) was used to quantitate adherent bacteria.

RESULTS

P. aeruginosa ATCC 19660 showed an increase in binding at pH 8.0, favored higher temperatures and required both calcium and magnesium for optimum binding. Adherence of PAO1 was enhanced at pH 6.5 and decreased at pH 8.0. This strain favored binding at lower temperatures and did not require either divalent cation for optimum binding. In addition, the presence of magnesium ions resulted in reduced binding for this strain. Both strains exhibited less binding ability after formalin fixation or heat killing.

CONCLUSION

Environmental factors and bacterial viability are important factors which influence the ability of both cytotoxic and invasive strains of P. aeruginosa to bind to the scarified cornea.