Antigen heterogeneity among isolates of Mycoplasma bovis is generated by high-frequency variation of diverse membrane surface proteins

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.

Toward a Method for Harmonized Susceptibility Testing of Mycoplasma bovis by Broth Microdilution

Mycoplasma bovis is a fastidious pathogen of cattle causing massive economic losses in the calf and dairy industries worldwide. Since there is no approved standard method for antimicrobial susceptibility testing (AST) of M. bovis, the Clinical and Laboratory Standards Institute has requested the development of a suitable method. Therefore, this study aimed at developing a method for harmonized broth microdilution AST of M. bovis. For this, 131 M. bovis field isolates and M. bovis strain DSM 22781T were collected and macrorestriction analysis was performed to select 15 epidemiologically unrelated M. bovis strains for method validation steps. To select a suitable broth for AST of M. bovis, growth determinations were performed using five media and growth curves were compiled. Then, susceptibility testing was performed considering the exact (precondition of five identical MICs) and essential (MIC mode, accepting a deviation of ±1 dilution step) MIC agreements to evaluate the reproducibility of MIC values using a panel of 16 antimicrobial agents. Subsequently, the remaining field isolates were tested and the suitability of quality control (QC) strains was assessed. Growth experiments showed that SP4 broth was the only one of the five media that yielded sufficient growth of M. bovis. Therefore, it was selected as the test medium for AST and homogeneous MIC values were obtained (exact and essential agreements of 36 to 100% and 92 to 100%, respectively). For all other isolates tested, easy-to-read MIC endpoints were determined with this medium. High overall MIC50 and/or MIC90 values were observed for aminoglycosides and macrolides, and some isolates showed elevated MICs of fluoroquinolones, gentamicin, and/or tiamulin. Since the MICs of four commonly used QC strains were partially not within their ranges, a 20-fold MIC testing of M. bovis DSM 22781T was performed and met the criteria for a new QC strain. For harmonized AST of M. bovis, SP4 broth seems to be suitable with an incubation time of 72 ± 2 h and further validation of M. bovis DSM 22781T as a future QC strain is recommended.

Infection, Transmission, Pathogenesis and Vaccine Development against Mycoplasma gallisepticum

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

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

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

Mycoplasma bovis Mastitis

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Mycoplasma bovis mastitis (MBM) is highly contagious and causes significant economic losses through reduction in milk quantity and quality, culling and treatment costs.

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Adhesion and invasion are among the most important virulence mechanisms to establish infection in the mammary gland.

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M. bovis can elicit both humoral and cellular immune responses during mammary gland infection.

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There is no effective commercial vaccine against MBM to date and early detection and isolation/culling remains vital control measure for MBM in dairy farms.

Bovine mycoplasmoses, which is mostly caused by Mycoplasma bovis, is a significant problem in the dairy and beef industry. Mycoplasmal mastitis has a global occurrence with notable effects in the United States and Europe. The pathogen was first detected in a mastitis case in California, United States, and regarded as major contagious mastitis. It is highly contagious and resistant to antibiotics and lack cell wall rendering certain group of antibiotics ineffective. Outbreaks mostly originate from introduction of diseased dairy cows to a farm and poor hygienic practices that help to maintain cow to cow transmission. Rapid detection scheme is needed to be in place in dairy farms to devise preventive measures and stop future outbreaks. However; early detection is hampered by the fastidious growth of M. bovis and the need for specialized equipment and reagents in laboratory settings. Intramammary Mycoplasma bovis infections cause elevation in milk somatic cell count which is one of the important factors to determine milk quality for grading and hence dictates milk price. There are multiple attributes of M. bovis regarded as virulence factors such as adhesion to and invasion into host cells, avoidance of phagocytosis, resistance to killing by the alternative complement system, biofilm formation, and hydrogen peroxide production.

Nevertheless, there are still undetermined virulence factors that hamper the development of sustainable control tools such as effective vaccine. To date, most vaccine trials have failed, and there is no commercial M. bovis mastitis vaccine. Mycoplasma bovis has been shown to modulate both humoral and cellular immune response during bovine mastitis. In the future, research seeking new immunogenic and protective vaccine targets are highly recommended to control this important dairy cattle disease worldwide.

Bacterial Conjugation Protocol for Ruminant Mycoplasmas

In Mycoplasma agalactiae, two simultaneous processes of DNA transfer have been described that require direct cell-to-cell contact and are similar to conjugation. One involves the self-transmission of an integrative conjugative element (ICE) while the second concerns the horizontal transfer of large and small fragments of chromosomal DNA. Here, we describe an optimized conjugation protocol for the horizontal transfer of ICE or chromosomal DNA carrying antibiotic resistance markers (i.e., tetracycline, gentamicin, puromycin) from donor to recipient mycoplasma cells. Calculation of the conjugation frequencies, selection and characterization of transconjugants are detailed. This protocol has been developed with M. agalactiae but has been successfully used for M. bovis and can be adapted to other related mycoplasma species.

Prevalência e estudo genético de Mycoplasma gallisepticum e M. synoviae em poedeiras comerciais, na região centro-oeste do estado de São Paulo, Brasil

RESUMO O objetivo deste trabalho foi estudar a prevalência de MG e MS e a filogenia das cepas circulantes, comparando-as com outras já descritas em poedeiras comerciais no Brasil. Foram coletados 140 suabes traqueais de poedeiras comerciais com sinais respiratórios em seis granjas da região centro-oeste de São Paulo. As amostras foram avaliadas por PCR, com posterior sequenciamento e análise filogenética das cepas identificadas. Das 140 amostras, 16,4% foram positivas para MG e 68,6% para MS. Houve diferença significativa nas frequências de MG e MS por granja, segundo o teste G de independência (P<0,05). Todas as cepas identificadas de MG e MS de granjas distintas apresentaram similaridade tanto pela lipoproteína para MG quanto pela região 16s rRNA para MS. Neste estudo, foi possível observar altas prevalências dos agentes estudados, sendo a de MS maior que a de MG. Foi detectada infecção mista por MG e MS em 11,4% das amostras e sabe-se que esses micoplasmas podem agir de forma sinérgica, agravando o quadro respiratório. As cepas circulantes identificadas, pela análise das regiões gênicas da lipoproteína para MG e 16S rRNA para MS, são similares em todas as granjas estudadas.

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.

Genomics-based epidemiology of bovine Mycoplasma bovis strains in Israel

Background

Mycoplasma bovis is an important etiologic agent of bovine mycoplasmosis affecting cattle production and animal welfare. In the past in Israel, M. bovis has been most frequently associated with bovine respiratory disease (BRD) and was rarely isolated from mastitis. This situation changed in 2008 when M. bovis-associated mastitis emerged in Israel. The aim of this study was to utilize whole genome sequencing to evaluate the molecular epidemiology and genomic diversity of M. bovis mastitis-associated strains and their genetic relatedness to M. bovis strains isolated from BRD in local feedlot calves and those imported to Israel from different European countries and Australia.

Results

Phylogeny based on total single nucleotide polymorphism (SNP) analysis of 225 M. bovis genomes clearly showed clustering of isolates on the basis of geographical origin: strains isolated from European countries clustered together and separately from Australian and Chinese isolates, while Israeli isolates were found in the both groups. The dominant genotype was identified among local mastitis-associated M. bovis isolates. This genotype showed a close genomic relatedness to M. bovis strains isolated from calves imported to Israel from Australia, to original Australian M. bovis strains, as well as to strains isolated in China.

Conclusions

This study represents the first comprehensive high-resolution genome-based epidemiological analysis of M. bovis in Israel and illustrates the possible dissemination of the pathogen across the globe by cattle trade.

Proteases as Secreted Exoproteins in Mycoplasmas from Ruminant Lungs and Their Impact on Surface-Exposed Proteins

Many mycoplasma species are isolated from the ruminant lungs as either saprophytes or true pathogens. These wall-less bacteria possess a minimal genome and reduced metabolic capabilities. Accordingly, they rely heavily on their hosts for the supply of essential metabolites and, notably, peptides. Seven of 13 ruminant lung-associated Mycoplasma (sub)species were shown to possess caseinolytic activity when grown in rich media and assessed with a quantitative fluorescence test. For some species, this activity was detected in spent medium, an indication that proteases were secreted outside the mycoplasma cells. To identify these proteases, we incubated concentrated washed cell pellets in a defined medium and analyzed the supernatants by tandem mass spectrometry. Secreted-protease activity was detected mostly in the species belonging to the Mycoplasma mycoides cluster (MMC) and, to a lesser extent, in Mycoplasma bovirhinis Analyzing a Mycoplasma mycoides subsp. capri strain, chosen as a model, we identified 35 expressed proteases among 55 predicted coding genes, of which 5 were preferentially found in the supernatant. Serine protease S41, acquired by horizontal gene transfer, was responsible for the caseinolytic activity, as demonstrated by zymography and mutant analysis. In an M. capricolum mutant, inactivation of the S41 protease resulted in marked modification of the expression or secretion of 17 predicted surface-exposed proteins. This is an indication that the S41 protease could have a role in posttranslational cleavage of surface-exposed proteins and ectodomain shedding, whose physiological impacts still need to be explored.IMPORTANCE Few studies pertaining to proteases in ruminant mycoplasmas have been reported. Here, we focus on proteases that are secreted outside the mycoplasma cell using a mass spectrometry approach. The most striking result is the identification, within the Mycoplasma mycoides cluster, of a serine protease that is exclusively detected outside the mycoplasma cells and is responsible for casein digestion. This protease may also be involved in the posttranslational processing of surface proteins, as suggested by analysis of mutants showing a marked reduction in the secretion of extracellular proteins. By analogy, this finding may help increase understanding of the mechanisms underlying this ectodomain shedding in other mycoplasma species. The gene encoding this protease is likely to have been acquired via horizontal gene transfer from Gram-positive bacteria and sortase-associated surface proteases. Whether this protease and the associated ectodomain shedding are related to virulence has yet to be ascertained.

Mycoplasma Chromosomal Transfer: A Distributive, Conjugative Process Creating an Infinite Variety of Mosaic Genomes

The capacity of Mycoplasmas to engage in horizontal gene transfers has recently been highlighted. Despite their small genome, some of these wall-less bacteria are able to exchange multiple, large portions of their chromosome via a conjugative mechanism that does not conform to canonical Hfr/oriT models. To understand the exact features underlying mycoplasma chromosomal transfer (MCT), extensive genomic analyses were performed at the nucleotide level, using individual mating progenies derived from our model organism, Mycoplasma agalactiae. Genome reconstruction showed that MCT resulted in the distributive transfer of multiple chromosomal DNA fragments and generated progenies composed of a variety of mosaic genomes, each being unique. Analyses of macro- and micro-events resulting from MCT revealed that the vast majority of the acquired fragments were unrelated and co-transferred independently from the selection marker, these resulted in up to 17% of the genome being exchanged. Housekeeping and accessory genes were equally affected by MCT, with up to 35 CDSs being gained or lost. This efficient HGT process also created a number of chimeric genes and genetic micro-variations that may impact gene regulation and/or expression. Our study unraveled the tremendous plasticity of M. agalactiae genome and point toward MCT as a major player in diversification and adaptation to changing environments, offering a significant advantage to this minimal pathogen.

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.

The Performance of Three Immune Assays to Assess the Serological Status of Cattle Experimentally Exposed to Mycoplasma bovis

Mycoplasma bovis is associated with several clinical syndromes of cattle. Currently, limited information is available on the sensitivity (Se) and specificity (Sp) of serological assays used for the detection of M. bovis-specific antibodies. Consequently, it is difficult to critically evaluate the outcomes of studies that use these assays. Therefore, the current study used bovine sera sourced from M. bovis exposure studies from three countries to estimate the Se and Sp of two commercial M. bovis enzyme-linked immunosorbent assays (ELISA), BIO K302 and BIO K260, and Western blotting. Western blotting had the highest Se estimate of 74% (95% confidence interval (CI): 16–98%), compared to the BIO K302: 47% (95% CI: 10–87%) and BIO K260: 28% (95% CI: 1–92%). However, for Sp, the BIO K302: 96% (95% CI: 87–99%) and the BIO K260: 100% (95% CI: 93–100%) out-performed Western blotting: 88% (95% CI: 56–98%). Western blotting was the best assay for detecting seroconversion, correctly identifying 61% (95% CI: 29–86%) of exposed animals compared to 35% for BIO K302 (95% CI: 21–54%) and 8% for BIO K260 (95% CI: 0–87%). While none of the methods assessed had high Se and Sp, the availability of these estimates will aid in the interpretation of studies that use these assays. The results of this study highlight the difficulties encountered when using serology to detect exposure to M. bovis in cattle.

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.

Prevalence of pathogens from Mollicutes class in cattle affected by respiratory diseases and molecular characteristics of Mycoplasma bovis field strains

Introduction: Mycoplasma bovis is one of the main pathogens involved in cattle pneumonia. Other mycoplasmas have also been directly implicated in respiratory diseases in cattle. The prevalence of different Mycoplasma spp. in cattle affected by respiratory diseases and molecular characteristics of M. bovis field strains were evaluated. Material and Methods: In total, 713 nasal swabs from 73 cattle herds were tested. The uvrC gene fragment was amplified by PCR and PCR products were sequenced. PCR/DGGE and RAPD were performed. Results: It was found that 39 (5.5%) samples were positive for M. bovis in the PCR and six field strains had point nucleotide mutations. Additionally, the phylogenetic analysis of 20 M. bovis field strains tested with RAPD showed two distinct groups of M. bovis strains sharing only 3.8% similarity. PCR/DGGE analysis demonstrated the presence of bacteria belonging to the Mollicutes class in 79.1% of DNA isolates. The isolates were identified as: Mycoplasma bovirhinis, M. dispar, M. bovis, M. canis, M. arginini, M. canadense, M. bovoculi, M. alkalescens, and Ureaplasma diversum. Conclusion: Different Mycoplasma spp. strains play a crucial role in inducing respiratory diseases in cattle.

High Prevalence of Diverse Insertion Sequences within the rRNA Operons of Mycoplasma bovis

Insertion sequences (ISs) are widespread in the genome of Mycoplasma bovis strain PG45, but no ISs were identified within its two tandemly positioned rRNA operons (rrn1 and rrn2). However, characterization of the rrn locus in 70 M. bovis isolates revealed the presence of ISs related to the ISMbov1 (IS30 family) and ISMbov4 (IS4 family) isomers in 35 isolates. ISs were inserted into intergenic region 1 (IGR-1) or IGR-3, which are the putative promoter regions of rrn1 and rrn2, respectively, and into IGR-5, located downstream of the rrl2 gene. Seven different configurations (A to G) of the rrn locus with respect to ISs were identified, including those in five annotated genomes. The transcriptional start site for the single rrn operon in M. bovis strain 88127 was mapped within IGR-1, 60 bp upstream of the rrs gene. Notably, only 1 nucleotide separated the direct repeat (DR) for ISMbov1 and the promoter -35 element in configuration D, while in configuration F, the -35 motif was a part of the ISMbov1 DR. Relative quantitative real-time (qRT) PCR analysis and growth rate comparisons detected a significant increase (P < 0.05) in the expression of the rrs genes and in the number of viable cells during log phase growth (8, 12, and 16 h) in the strains with configuration F in comparison to strains with one or two rrn operons that did not have ISs. A high prevalence of IS elements within or close to the M. bovis rrn operon-promoter region may reflect their important role in regulation of both ribosome synthesis and function.

IMPORTANCE

Data presented in this study show a high prevalence of diverse ISs within the M. bovis rrn locus resulting in intraspecies variability and diversity. Such abundance of IS elements near or within the rrn locus may offer a selective advantage to M. bovis Moreover, the fact that expression of the rrs genes as well as the number of viable cells increased in the group of strains with IS element insertion within a putative promoter -35 sequence (configuration F) in comparison to that in strains with one or two rrn operons that do not have ISs may serve as a basis for understanding the possible role of M. bovis IS elements in fundamental biological processes such as regulation of ribosome synthesis and function.

Naturally Occurring Mycoplasma Bovis—Associated Pneumonia and Polyarthritis in Feedlot Beef Calves

Mycoplasma bovis is perceived as an emerging cause of mortality in feedlot beef cattle. This study examined the lesions and infectious agents in naturally occurring M. bovis–associated bronchopneumonia and arthritis and the relationship of this condition with bovine viral diarrhea virus (BVDV) infection. Standardized pathologic, immunohistochemical, and microbiologic investigations were conducted on 99 calves that died or were euthanized within 60 days after arrival in 72 feedlots. Cranioventral bronchopneumonia with multiple foci of caseous necrosis was identified in 54 of 99 calves, including 30 with concurrent fibrinosuppurative bronchopneumonia typical of pneumonic pasteurellosis. Mycoplasma bovis was consistently identified in these lesions by culture and immunohistochemistry, but also commonly in healthy lungs and those with pneumonia of other causes. Focal lesions of coagulation necrosis, typical of pneumonic pasteurellosis, were often infected with both Mannheimia haemolytica and M. bovis. Arthritis was present in 25 of 54 (46%) calves with M. bovis pneumonia, and all calves with arthritis had pneumonia. BVDV infection was more common in calves with lesions of bacterial pneumonia than in those dying of other causes, but BVDV infection was not more common in calves with caseonecrotic bronchopneumonia than those with fibrinosuppurative bronchopneumonia. Retrospective analysis identified cases of M. bovis pneumonia in the early 1980s that had milder lesions than the current cases. The findings suggest that, in at least some calves, M. bovis induces caseonecrotic bronchopneumonia within the lesions of pneumonic pasteurellosis.

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.

Severe Mycoplasma bovis outbreak in an Austrian dairy herd

A conventional dairy farm, housing 19 Austrian Simmental cows, experienced a spontaneous outbreak of a Mycoplasma bovis infection, showing severe clinical signs of respiratory tract disease, clinical mastitis, and tremendous drop in milk production. Despite intensive therapy, 5 cows died within 2 weeks or were euthanized. From the remaining cows, bacteriological culture and polymerase chain reaction revealed M. bovis in 10 of 14 milk samples. Mycoplasma bovis was found in 1 of 5 randomly collected nasal swabs. Autopsy of 1 cow revealed infection of the lungs and the udder with M. bovis. The 13 M. bovis isolates from milk samples, nasal swabs, lungs, and udder were genotyped by multilocus variable number of tandem-repeat analysis, and indicated that described infections were caused by a single M. bovis strain. The virulent M. bovis strain resulted in dramatic economic loss to the farmer. To control the disease, culling of all animals, including heifers and calves, was recommended, and strict hygienic measures were implemented before introducing new animals to the farm.

16S rRNA gene mutations associated with decreased susceptibility to tetracycline in Mycoplasma bovis

Mycoplasma bovis isolates with decreased susceptibilities to tetracyclines are increasingly reported worldwide. The acquired molecular mechanisms associated with this phenomenon were investigated in 70 clinical isolates of M. bovis. Sequence analysis of the two 16S rRNA-encoding genes (rrs3 and rrs4 alleles) containing the primary binding pocket for tetracycline (Tet-1 site) was performed on isolates with tetracycline hydrochloride MICs of 0.125 to 16 μg/ml. Mutations at positions A965T, A967T/C (Escherichia coli numbering) of helix 31, U1199C of helix 34, and G1058A/C were identified. Decreased susceptibilities to tetracycline (MICs, ≥2 μg/ml) were associated with mutations present at two (A965 and A967) or three positions (A965, A967, and G1058) of the two rrs alleles. No tet(M), tet(O), or tet(L) determinants were found in the genome of any of the 70 M. bovis isolates. The data presented correlate (P<0.0001) the mutations identified in the Tet-1 site of clinical isolates of M. bovis with decreased susceptibility to tetracycline.

Histopathological findings, phenotyping of inflammatory cells, and expression of markers of nitritative injury in joint tissue samples from calves after vaccination and intraarticular challenge with Mycoplasma bovis strain 1067

Background

The pathogenesis of caseonecrotic lesions developing in lungs and joints of calves infected with Mycoplasma bovis is not clear and attempts to prevent M. bovis-induced disease by vaccines have been largely unsuccessful. In this investigation, joint samples from 4 calves, i.e. 2 vaccinated and 2 non-vaccinated, of a vaccination experiment with intraarticular challenge were examined. The aim was to characterize the histopathological findings, the phenotypes of inflammatory cells, the expression of class II major histocompatibility complex (MHC class II) molecules, and the expression of markers for nitritative stress, i.e. inducible nitric oxide synthase (iNOS) and nitrotyrosine (NT), in synovial membrane samples from these calves. Furthermore, the samples were examined for M. bovis antigens including variable surface protein (Vsp) antigens and M. bovis organisms by cultivation techniques.

Results

The inoculated joints of all 4 calves had caseonecrotic and inflammatory lesions. Necrotic foci were demarcated by phagocytic cells, i.e. macrophages and neutrophilic granulocytes, and by T and B lymphocytes. The presence of M. bovis antigens in necrotic tissue lesions was associated with expression of iNOS and NT by macrophages. Only single macrophages demarcating the necrotic foci were positive for MHC class II. Microbiological results revealed that M. bovis had spread to approximately 27% of the non-inoculated joints. Differences in extent or severity between the lesions in samples from vaccinated and non-vaccinated animals were not seen.

Conclusions

The results suggest that nitritative injury, as in pneumonic lung tissue of M. bovis-infected calves, is involved in the development of caseonecrotic joint lesions. Only single macrophages were positive for MHC class II indicating down-regulation of antigen-presenting mechanisms possibly caused by local production of iNOS and NO by infiltrating macrophages.

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.

Membrane proteins of Mycoplasma bovis and their role in pathogenesis

Mycoplasma membrane proteins influence cell shape, cell division, motility and adhesion to host cells, and are thought to be integrally involved in the pathogenesis of mycoplasmoses. Many of the membrane proteins predicted from mycoplasma genome sequences remain hypothetical, as their presence in cellular protein preparations is yet to be established experimentally. Recent genome sequences of several strains of Mycoplasma bovis have provided further insight into the potential role of the membrane proteins of this pathogen in colonisation and infection. This review highlights recent advances in knowledge about the influence of M. bovis membrane proteins on the pathogenesis of infection with this species and identifies future research directions for enhancing our understanding of the role of these proteins.

Long-term survival of Mycoplasma bovis in necrotic lesions and in phagocytic cells as demonstrated by transmission and immunogold electron microscopy in lung tissue from experimentally infected calves

In the lungs of cattle infected with Mycoplasma bovis persistence of the agent for several weeks after infection has been demonstrated by different methods, e.g. isolation of the organism, immunohistochemistry for antigens, and in situ hybridization. The presence of macrophages and neutrophils with cytoplasmic M. bovis antigen suggests that phagocytosis occurs in vivo. It is, however, unknown whether this intracellular immunolabeling detected residual antigen after phagocytosis of M. bovis or surviving organisms in macrophages that use the intracellular survival as a strategy for evasion of the immune response. The aim of this electron microscopic investigation was to study the distribution of M. bovis within caseonecrotic lung lesions and to examine the phagocytes for intracellular presence of the agent. In lung tissue sections from 9 experimentally infected calves originating from two different infection experiments large numbers of mycoplasmas were detected by transmission electron microscopy and by immunogold electron microscopy using M. bovis-specific polyclonal antibodies. M. bovis were found throughout caseonecrotic foci and within the lumen of bronchi containing exudate. The majority of mycoplasmas were located extracellularly within necrotic lung lesions and around neutrophilic granulocytes and macrophages, while fewer organisms were found within the cytoplasm of phagocytes. The results of this study show that there is long-time survival of numerous intact M. bovis in necrotic lung lesions even though large numbers of neutrophils and macrophages are present. These findings show that the phagocytes are not able to eliminate M. bovis from the lungs from necrotic and inflamed lung tissue and indicate that persistence of the agent is possibly due to its capacity to avoid phagocytosis.

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 real-time polymerase chain reaction assay validation and diagnostic performance

Mycoplasma bovis is an important bacterial pathogen in cattle, producing a variety of clinical diseases. The organism, which requires specialized culture conditions and extended incubation times to isolate and identify, is frequently associated with concurrent infection with other pathogens which can potentially be more easily identified. Real-time polymerase chain reaction (real-time PCR) is a valuable diagnostic technique that can rapidly identify infectious agents in clinical specimens. A real-time PCR assay was designed based on the uvrC gene to identify M. bovis in diagnostic samples. Using culture as the gold standard test, the assay performed well in a variety of diagnostic matrices. Initial validation testing was conducted on 122 milk samples (sensitivity: 88.9% [95% confidence interval (CI): 68.4-100%], specificity: 100%); 154 lung tissues (sensitivity: 89.0% [95% CI: 83.1-94.9%], specificity: 97.8% [95% CI: 93.5-100%]); 70 joint tissue/fluid specimens (sensitivity: 92.3% [95% CI: 82.1-100%], specificity: 95.5% [95% CI: 89.3-100%]); and 26 nasal swabs (sensitivity: 75.0% [95% CI: 45.0-100%], specificity: 83.3% [95% CI: 66.1-100%]). Low numbers of other sample matrices showed good agreement between results of culture and PCR. A review of clinical cases from 2009 revealed that, in general, PCR was used much more frequently than culture and provided useful diagnostic information in conjunction with clinical signs, signalment, and gross and histopathologic lesions. Diagnostic performance of the real-time PCR assay developed as a testing method indicates that it is a rapid, accurate assay that is adaptable to a variety of PCR platforms and can provide reliable results on an array of clinical samples.

Expression of Mycoplasma bovis variable surface membrane proteins in the respiratory tract of calves after experimental infection with a clonal variant of Mycoplasma bovis type strain PG45

The pathomorphological findings and the expression and distribution of variable surface protein antigens (Vsp) of Mycoplasma (M.) bovis were characterised immunohistochemically in lungs of eight calves following inoculation with a Vsp A-expressing clonal variant of M. bovis type strain PG45. Within 48 h post inoculation (p.i.) an innate immune response dominated by macrophages and neutrophils develops. The monoclonal antibodies (mAbs) 1A1 and 1E5 detected M. bovis Vsp antigens in paraffin tissue sections of seven calves. Vsp antigens were widely distributed and were already present at day two p.i. within macrophages and other lung compartments. Taken together, the results demonstrate that the bovine is unable to eliminate M. bovis during the time period examined. Based on the different immunohistochemical labelling patterns obtained with the mAbs, the results also support the speculation that the in vivo variability of Vsps together with immunological factors may contribute to the chronicity of pulmonary disease.

Outbreak of Streptococcus equi subsp. zooepidemicus infections in cats

Streptococcus equi subsp. zooepidemicus (S. zooepidemicus) is a commensal of the mucous membranes and skin of animals, notably equine, and is associated with various infections in animals and humans. Here, we describe an outbreak of respiratory disease in a cattery, which, to the best of our knowledge, is the first report of S. zooepidemicus infection in cats. Clinical disease was characterized firstly by abundant purulent nasal discharges and cough, progressing to sinusitis, dyspnea, symptoms of pneumonia and death. Pathological examination revealed different degrees of inflammation of the lower respiratory tract. S. zooepidemicus was the main bacteria isolated. Sequencing of the V2 fragment of the 16S gene revealed that the isolates were distributed in two previously described genogroups.

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.

Molecular characterization of the Mycoplasma bovis p68 gene, encoding a basic membrane protein with homology to P48 of Mycoplasma agalactiae

Mycoplasmal lipoproteins are considered to be potential virulence determinants, which may carry out numerous important functions in pathogenesis including adhesion and immunomodulation. The prototype mycoplasmal immunomodulin is the macrophage-activating lipoprotein (MALP) of Mycoplasma fermentans. In this study, a homolog of the malp gene, designated p68, was identified and characterized in Mycoplasma bovis strain PG45 clonal variant #6. P68 belongs to the family of basic membrane proteins, which have been identified in diverse prokaryotes, including mycoplasmas. P68 revealed significant similarity and shared conserved selective lipoprotein-associated motifs with the highly immunogenic MALP-related lipoproteins P48 of M. bovis and P48 of Mycoplasma agalactiae. Determination of the genomic distribution of both M. bovis malp-homologs showed that p48 was present in all M. bovis strains tested, whereas the p68 gene was missing in some. Sequence comparison of the p68 genomic region in strains with and without this gene revealed that the region is very dynamic, with multiple genetic changes. Reverse-transcription PCR and primer extension analysis indicated that both p68 and p48 are transcribed in M. bovis under in vitro growth conditions. Mycoplasma bovis is the first mycoplasma species in which two malp-related genes have been identified.

Detection of Mycoplasma bovis with an improved pcr assay

A Mycoplasma bovis species-specific PCR assay has been developed with improvement of a previously described method (Ghadersohi et al., 1997). This test and its semi-nested version (Hayman and Hirst, 2003) did not function at all in our hands. A new reverse primer (Mbr2) was designed using previously published sequence data. For testing specificity, DNA was extracted from the most frequently occurring mycoplasma species and bacteria of bovine origin. The new PCR detected only Mycoplasma bovis. Moreover, no cross-reaction was observed with the genetically closest relative species, M. agalactiae. The target organism could be detected in a dose as low as 150 CFU ml(-1) in broth cultures using ethidium-bromide-stained agarose gels.

Mycoplasma Mastitis: A Review of Transmission and Control

The Mycoplasma sp. that cause mastitis are simple, cell wall-less, bacteria that can colonize and cause diseases in other extramammary sites in the bovine. Prevalence of mycoplasma mastitis appears to be increasing in many locations throughout the world. The best method to identify this group of pathogens is through direct culture on mycoplasma agar media. However, limitations with this culture procedure are the duration of culture, 10 days, special conditions required and thus added expense, and the lack of primary specificity to distinguish between true pathogens and commensal organisms. Thus culture of bulk tank milk samples has been advocated as a primary screening method to determine the mycoplasma status of a herd. This monitoring system is reasonably successful but the sensitivity of detection of Mycoplasma sp. in bulk tank milk is affected by a significant minority of cows that might shed the organism at levels below the threshold of detection. Contagious mastitis control procedures have been effective in controlling outbreaks of mycoplasma mastitis. Yet new methods of control might be warranted, methods that may prevent the outbreak. Current data suggests that a significant number of new outbreaks may occur via internal or animal-to-animal transmission of mycoplasma mastitis pathogens from asymptomatic carriers.

First steps towards the genetic manipulation of Mycoplasma agalactiae and Mycoplasma bovis using the transposon Tn4001mod

Mycoplasma agalactiae and M. bovis rank amongst the most serious pathogenic mycoplasmas infecting small ruminants and cattle, respectively. Despite considerable advances made in Mycoplasma molecular genetics in the past decade, there is still a complete lack of genetic tools to assess the pathogenic mechanisms of these two species. Studies were undertaken to develop a genetic system for the analysis of potential virulence factors of these pathogens. Transposon Tn4001mod was successfully introduced into various chromosomal sites of M. agalactiae and M. bovis with an optimal frequency of 10(-6) per viable colony-forming unit (CFU). This is the first report that demonstrates the amenability of these agents to transformation and to genetic manipulation. Furthermore, Tn4001 is implicated as the first potential genetic tool available for these ruminant pathogens.

Molecular epidemiological analysis of Mycoplasma bovis isolates from the United Kingdom shows two genetically distinct clusters

Mycoplasma bovis is an important veterinary pathogen causing pneumonia, arthritis, and mastitis in infected cattle. We investigated the genetic diversity of 53 isolates collected in the United Kingdom between 1996 and 2002 with pulsed-field gel electrophoresis (PFGE), amplified fragment length polymorphism (AFLP), and random amplified polymorphic DNA (RAPD) analysis. In addition, the influence of variable surface protein (Vsp) profiles on the profiles generated with molecular typing techniques was studied. Both AFLP and RAPD separated the isolates into two distinct groups, but PFGE showed less congruence with the other techniques. There was no clear relationship between the geographic origin or year of isolation of the isolates and the profiles produced. No correlation between Vsp profiles and any of the molecular typing techniques was observed. We propose that RAPD and AFLP provide valuable tools for molecular typing of M. bovis.

Cytadherence-deficient mutants of Mycoplasma gallisepticum generated by transposon mutagenesis

Cytadherence-related molecules of Mycoplasma gallisepticum strain R-low were identified by Tn4001 transposon mutagenesis with the hemadsorption (HA) assay as an indicator for cytadherence. Three Gm(r) HA-negative (HA(-)) colonies displaying a stable HA(-) phenotype through several successive generations in which gentamicin selection was maintained were isolated from four independent transformation experiments and characterized. Southern blot analysis showed that the transposon was inserted as a single copy within the genome of each of the HA(-) mutants, suggesting that the transposon insertion was directly responsible for their inability to attach to erythrocytes. Sequence analysis of the transposon insertion sites revealed that in two mutants, the transposon was inserted at two distinct sites within the gapA structural gene. In the third mutant, the insertion was mapped within the crmA gene, which is located immediately downstream of the gapA gene as part of the same operon. In vitro attachment experiments with the MRC-5 human lung fibroblast cell line showed that the cytadherence capabilities of the HA(-) mutants were less than 25% those of original strain R. Experimental infection of chickens, the natural host of M. gallisepticum, with each of the three mutants demonstrated significantly impaired colonization and host responses. These data demonstrate conclusively the role of both GapA and CrmA proteins in the adherence of M. gallisepticum to host cells in model systems and in vivo colonization. Furthermore, these results underscore the relevance of in vitro cytadherence model systems for studying the pathogenesis of natural infections in chickens.

Molecular epidemiology of Mycoplasma conjunctivae in Caprinae: transmission across species in natural outbreaks

Mycoplasma conjunctivae is the etiological agent of infectious keratoconjunctivitis, a highly contagious ocular infection that affects both domestic and wild Caprinae species in the European Alps. In order to study the transmission and spread of M. conjunctivae across domestic and wild Caprinae populations, we developed a molecular method for subtyping and identifying strains of M. conjunctivae. This method is based on DNA sequence determination of a variable domain within the gene lppS, a gene that encodes an antigenic lipoprotein of M. conjunctivae. This domain of lppS shows variations among different strains but remains constant upon generations of individual strains on growth medium and thus allows identification of individual strains and estimation of their phylogenetic intercorrelations. The variable domain of lppS is amplified by PCR using primers that match conserved sequences of lppS flanking it. Sequence analysis of the amplified fragment enables fine subtyping of M. conjunctivae strains. The method is applicable both to isolated strains and to clinical samples directly without requiring the cultivation of the strain. Using this method, we show that M. conjunctivae was transmitted between domestic and wild animals that were grazing in proximate pastures. Certain animals also presented infections with two different strains simultaneously.

Mycoplasmal mastitis in dairy herds

Mycoplasmal bovine mastitis is potentially a highly contagious disease that can cause severe economic problems in affected herds. The purchase of replacement heifers and cows are frequently the origin of mycoplasmal mastitis outbreaks in previously Mycoplasma-free herds. Purchased cows and heifers should be quarantined and tested for mycoplasmal mastitis before admission to the regular herd. Detection of Mycoplasma-infected cows by culture of milk is straightforward, although there are problems of sensitivity for its detection in milk samples that are inherent to the nature of the disease and laboratory procedures. After detection of infected cows, the best way to protect the herd is to culture all cows in the herd, cows with clinical mastitis, and all heifers and cows after calving and before entering the milking herd. Control of mycoplasmal mastitis requires test and culling from the herd of Mycoplasma-positive cows if possible. When a large number of cows are infected, strict segregation with adequate management is an option; however, animals in this group should never re-enter the Mycoplama-free herd. The functioning of the milking equipment and milking procedures should be evaluated carefully and any flaws corrected. There is no treatment for mycoplasmal mastitis, and vaccination has not proven to be efficacious to prevent, decrease the incidence, or ameliorate the clinical signs of mycoplasmal mastitis. Waste milk should not be fed to calves without pasteurization. M bovis may cause several other pathologies in animals of different ages on a farm, including pneumonia, arthritis, and ear infections. The survival of mycoplasmas in different farm microenvironments needs to be further investigated for its impact on the epidemiology of the disease.

Recognition of multiple Mycoplasma bovis antigens by monoclonal antibodies

To produce monoclonal antibodies (MAbs), Balb/c AnN Crl BR mice were inoculated with the cell suspension of a Hungarian Mycoplasma bovis strain designated 26034. Three days after the last immunization the spleen of the immunized mouse was removed aseptically. The fusion of spleen cells with Sp2/0-Ag14 murine myeloma cells was performed in the presence of polyethylene glycol. The obtained hybrid cells were selected with hipoxantine, aminopterine and thymidine (HAT) medium. Two weeks after the fusion, the supernatants of the grown cells were tested by a self-developed indirect enzyme-linked immunosorbent assay (ELISA). The results showed that 63 antibody-producing hybridomas had been obtained. For accurate determination of the molecular weight of antigen determinants, the supernatants giving positive reaction in the ELISA were tested by Western blotting. According to the results, the obtained MAbs recognize the antigen determinants of the following molecular weights: 1B11: 63 kDa, 1C7: 63 kDa, 2C5: 22, 25 and 27 kDa, 2C9: 69 kDa, 3G12: 67, 69 and 72 kDa, 4H9: 63 kDa, 5B8: 22, 25 and 27 kDa, 5D3: 22, 25 and 27 kDa, 5C11: 69 kDa, 5E5: 22, 25 and 27 kDa, 6F11: 63 kDa, and 6H10: 22, 25 and 27 kDa. The 12 cell groups selected on the basis of the Western blotting were cloned twice by end-point dilution method. The cloned cells were propagated, and with 5 cell lines antibodies were produced in the CELLine bioreactor (Integra Biosciences, Zurich, Switzerland). Cell line 3G12 showed the highest productivity with an average daily output of 1.5 mg immunoglobulin. Cell line 5E5 produced 1.1 mg, 6H10 0.8 mg, 2C9 0.47 mg and 6F11 0.4 mg antibody per day. The isotype of the antibodies was determined by ELISA. The antibodies produced by the 12 cell lines tested were assigned to the IgG(1) subclass according to the heavy chain. Ten cell lines produced kappa and two produced lambda light-chain antibody. Possible cross-reactions of the produced monoclonal anti-M. bovis antibodies with certain Mycoplasma, Ureaplasma and Acholeplasma species were tested by an indirect ELISA procedure. All of the 12 antibodies tested gave a reaction with the antigen of M. bovis strain designated 26034. MAbs 3G12 (67, 69, and 72 kDa) and 5B8 (22, 25, and 27 kDa) gave no cross-reaction with antigens other than strains of the homologous Mycoplasma species. The other antibodies reacted with the M. bovigenitalium F7, M. anseris 8389, M. oculi, and M. gallisepticum s6 Holland antigens. Owing to its high specificity and affinity, the antibody produced by the cell line 3G12 is primarily considered suitable for use in immunodiagnostic tests of M. bovis infections.

Extended repertoire of genes encoding variable surface lipoproteins in Mycoplasma bovis strains

A genomic cluster of vsp genes was previously shown to mediate high-frequency phenotypic switching of surface lipoprotein antigens in the bovine pathogen Mycoplasma bovis. This study revealed that field strains of M. bovis possess modified versions of the vsp gene complex in which extensive sequence variations occur primarily in the reiterated coding sequences of the vsp structural genes. These findings demonstrate that there is a vastly expanded potential for antigenic variation within populations of this organism.

Serological prevalence of Mycoplasma bovis infection in suckling beef cattle in France

The prevalence of Mycoplasma bovis infection in France was assessed by means of a serological survey of suckling beef cattle, using an ELISA. The survey included 824 randomly selected herds in eight French counties and a total of 32,197 animals more than one year old. In each county, the number of herds tested was determined statistically on the basis of the hypothesis that about 40 per cent of herds are infected. The proportion of herds containing at least one infected animal ranged from 28 to 90 per cent depending on the county. Among the 32,197 sera tested, the animal infection rate ranged between 2 per cent and 13 per cent. In infected herds, the average number of positive animals per herd was between 10 and 20 per cent, and the infection was unevenly distributed among the areas tested.

Phase variation among major surface antigens of Mycoplasma penetrans

The pathogenicity and prevalence of Mycoplasma penetrans, a Mycoplasma species recently isolated from humans, are still debated. A major P35 antigen, which is used as target epitope in serological assays, was shown to be a phase-variable lipid-associated membrane protein (LAMP). In this study, we performed a comparative analysis of the LAMP patterns from five M. penetrans clinical isolates and from the type strain. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis profiles and immunoblots with sera serially collected from an M. penetrans-infected patient indicated that these strains expressed different LAMP repertoires. Furthermore, the intraclonal variation in the expression of LAMPs (P34A, P34B, P35, and P38) was monitored by immunoblot analysis with three specific monoclonal antibodies (MAbs) developed in this study and MAb 7 to P35. The phase variation of these LAMPs occurs in an independent manner, with frequencies of variation ranging from 10(-2) to 10(-4) per cell per generation. Consistent with their amphipathic nature, the P34B and P38 antigens were found exposed at the cell surface. The DNA sequence encoding the P38 antigen was defined and found to be related to those of the P35 gene and other putative LAMP-encoding genes, suggesting that these variable antigens are encoded by a family of related genes. Finally, the serum samples from an M. penetrans-infected patient contained antibodies that reacted with a P36 antigen expressed in different M. penetrans strains but not in the isolate recovered from this patient. This result suggested that in vivo phase variation of P36 occurred, which would support a role for these LAMP variations in avoiding the host's immune vigilance.

Juxtaposition of an active promoter to vsp genes via site-specific DNA inversions generates antigenic variation in Mycoplasma bovis

Mycoplasma bovis, the most important etiological agent of bovine mycoplasmosis, undergoes extensive antigenic variation of major and highly immunogenic surface lipoprotein antigens (Vsps). A family of 13 related but divergent vsp genes, which occur as single chromosomal copies, was recently found in the chromosome of M. bovis. In the present study, the molecular mechanism mediating the high-frequency phase variation of two Vsps (VspA and VspC) as representatives of the Vsp family was investigated. Analysis of clonal isolates exhibiting phase transitions of VspA or of VspC (i.e., ON-->OFF-->ON) has shown that DNA inversions occur during Vsp phase variation. The upstream region of each vsp gene contains two sequence cassettes. The first (cassette no. 1), a 71-bp region upstream of the ATG initiation codon, exhibits 98% homology among all vsp genes, while the second (cassette no. 2), upstream of cassette no. 1, ranges in size from 50 to 180 bp and is more divergent. Examination of the ends of the inverted fragments during VspA or VspC phase variation revealed that in both cases, a change in the organization of vsp upstream cassettes involving three vsp genes had occurred. Primer extension and Northern blot analysis have shown that a specific cassette no. 2, designated A(2), is an active promoter and that juxtaposition of this regulatory element to a silent vsp gene by DNA inversions allows transcription initiation of the recipient gene. Further genetic analysis revealed that phase variation of VspA or of VspC involves two site-specific DNA inversions occurring between inverted copies of a specific 35-bp sequence present within the conserved cassette no. 1. A model for the control of Vsp phase variation is proposed.

Molecular variability of the adhesin-encoding gene pvpA among Mycoplasma gallisepticum strains and its application in diagnosis

Mycoplasma gallisepticum is an important pathogen of chickens and turkeys that causes considerable economic losses to the poultry industry worldwide. The reemergence of M. gallisepticum outbreaks among poultry, the increased use of live M. gallisepticum vaccines, and the detection of M. gallisepticum in game and free-flying song birds has strengthened the need for molecular diagnostic and strain differentiation tests. Molecular techniques, including restriction fragment length polymorphism of genomic DNA (RFLP) and PCR-based random amplification of polymorphic DNA (RAPD), have already been utilized as powerful tools to detect intraspecies variation. However, certain intrinsic drawbacks constrain the application of these methods. The main goal of this study was to determine the feasibility of using an M. gallisepticum-specific gene encoding a phase-variable putative adhesin protein (PvpA) as the target for molecular typing. This was accomplished using a pvpA PCR-RFLP assay. Size variations among PCR products and nucleotide divergence of the C-terminus-encoding region of the pvpA gene were the basis for strain differentiation. This method can be used for rapid differentiation of vaccine strains from field isolates by amplification directly from clinical samples without the need for isolation by culture. Moreover, molecular epidemiology of M. gallisepticum outbreaks can be performed using RFLP and/or sequence analysis of the pvpA gene.

Antigen heterogeneity and epitope variable expression in Mycoplasma meleagridis isolates

Immunoblotting was used to check the antigenic profiling of 27 Mycoplasma meleagridis strains isolated in different countries. Hyperimmune polyclonal rabbit antiserum as well as monoclonal antibodies (MAbs) raised against M. meleagridis (MM) showed antigen heterogeneity among strains. Five anti-MM MAbs were selected for lack of reaction against heterologous avian mycoplasma. Three of these five Mabs did not cross-react with 63 mycoplasma strains from six species affecting turkeys other than M. meleagridis. The five Mabs used to analyse the epitopes of 30 M. meleagridis strains indicated that some epitopes were not expressed in all strains. Moreover, other epitopes were located on proteins which differed according to number or molecular mass from strain to strain. The five Mabs therefore, recognised variable surface proteins, among which two were amphiphilic membrane proteins. Three of the selected Mabs recognised 29 or 30 of the 30 tested strains. The in vitro expression of surface epitopes in M. meleagridis ATCC 25284 was investigated by colony immunobinding and allowed demonstration of a variable antigenic system.