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

The Pathogenomics of the Respiratory Mycoplasma bovis Strains Circulating in Cattle Around the Texas Panhandle, USA

Bovine respiratory disease (BRD) is a major economic and animal welfare issue in the beef industry. Mycoplasma bovis is one of the main causal organisms, particularly in chronic cases. Due to the difficulty of isolating M. bovis from clinical isolates, there is a lack of information on the genetic diversity of this pathogen in the Texas panhandle region of the United States. Therefore, our objective was to provide genome-level characterization of M. bovis isolated from the lung lesions of beef and dairy cattle in the Texas panhandle. Fifty-four isolates displaying mycoplasma-like growth were recovered from bovine lung lesions by the Texas Veterinary Medical Diagnostic Laboratory in 2021 and 2022. Of these isolates, 32 were determined to be M. bovis via species-specific qPCR using the uvrC gene. Long-read whole-genome sequencing was used to identify key virulence factors, antimicrobial resistance genes, and to assess the genetic diversity of these isolates. Fisher's exact tests were used to identify associations between isolate characteristics and host metadata, including the state of origin, type of operation, animal age, and animal sex. Our results indicate that there is considerable genetic diversity among the M. bovis isolates, despite their shared geography in the Texas panhandle, though significant clustering based on host metadata was observed. Analysis of the pangenome showed that the M. bovis isolates in this study also harbor a diverse array of virulence genes, but no antimicrobial resistance genes were identified in this study.

Diversity and antigenic potentials of Mycoplasmopsis bovis secreted and outer membrane proteins within a core genome of strains isolated from North American bison and cattle

Mycoplasmopsis bovis is a worldwide economically important pathogen of cattle that can cause or indirectly contribute to bovine respiratory disease. M. bovis is also a primary etiological agent of respiratory disease in bison with high mortality rates. A major challenge in the development of an efficacious M. bovis vaccine is the design of antigens that contain both MHC-1 and MHC-2 T-cell epitopes, and that account for population level diversity within the species. Publicly available genomes and sequence read archive libraries of 381 M. bovis strains isolated from cattle (n = 202) and bison (n = 179) in North America were used to identify a core genome of 575 genes, including 38 that encode either known or predicted secreted or outer membrane proteins. The antigenic potentials of the proteins were characterized by the presence and strength of their T-cell epitopes, and their protein variant diversity at the population-level. The proteins had surprisingly low diversity and varying predictive levels of T-cell antigenicity. These results provide a reference for the selection or design of antigens for vaccine testing against strains infecting North American cattle and bison.

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.

De novo genome assembly resolving repetitive structures enables genomic analysis of 35 European Mycoplasmopsis bovis strains

Mycoplasmopsis (M.) bovis, the agent of mastitis, pneumonia, and arthritis in cattle, harbors a small genome of approximately 1 Mbp. Combining data from Illumina and Nanopore technologies, we sequenced and assembled the genomes of 35 European strains and isolate DL422_88 from Cuba. While the high proportion of repetitive structures in M. bovis genomes represent a particular challenge, implementation of our own pipeline Mycovista (available on GitHub www.github.com/sandraTriebel/mycovista ) in a hybrid approach enabled contiguous assembly of the genomes and, consequently, improved annotation rates considerably. To put our European strain panel in a global context, we analyzed the new genome sequences together with 175 genome assemblies from public databases. Construction of a phylogenetic tree based on core genes of these 219 strains revealed a clustering pattern according to geographical origin, with European isolates positioned on clades 4 and 5. Genomic data allowing assignment of strains to tissue specificity or certain disease manifestations could not be identified. Seven strains isolated from cattle with systemic circular condition (SCC), still a largely unknown manifestation of M. bovis disease, were located on both clades 4 and 5. Pairwise association analysis revealed 108 genomic elements associated with a particular clade of the phylogenetic tree. Further analyzing these hits, 25 genes are functionally annotated and could be linked to a M. bovis protein, e.g. various proteases and nucleases, as well as ten variable surface lipoproteins (Vsps) and other surface proteins. These clade-specific genes could serve as useful markers in epidemiological and clinical surveys.

Population Genomic Analysis of Mycoplasma bovis Elucidates Geographical Variations and Genes associated with Host-Types

Among more than twenty species belonging to the class Mollecutes, Mycoplasma bovis is the most common cause of bovine mycoplasmosis in North America and Europe. Bovine mycoplasmosis causes significant economic loss in the cattle industry. The number of M. bovis positive herds recently has increased in North America and Europe. Since antibiotic treatment is ineffective and no efficient vaccine is available, M. bovis induced mycoplasmosis is primarily controlled by herd management measures such as the restriction of moving infected animals out of the herds and culling of infected or shedders of M. bovis. To better understand the population structure and genomic factors that may contribute to its transmission, we sequenced 147 M. bovis strains isolated from four different countries viz. USA (n = 121), Canada (n = 22), Israel (n = 3) and Lithuania (n = 1). All except two of the isolates (KRB1 and KRB8) were isolated from two host types i.e., bovine (n = 75) and bison (n = 70). We performed a large-scale comparative analysis of M. bovis genomes by integrating 103 publicly available genomes and our dataset (250 total genomes). Whole genome single nucleotide polymorphism (SNP) based phylogeny using M.agalactiae as an outgroup revealed that M. bovis population structure is composed of five different clades. USA isolates showed a high degree of genomic divergence in comparison to the Australian isolates. Based on host of origin, all the isolates in clade IV was of bovine origin, whereas majority of the isolates in clades III and V was of bison origin. Our comparative genome analysis also revealed that M. bovis has an open pangenome with a large breadth of unexplored diversity of genes. The function based analysis of autogenous vaccine candidates (n = 10) included in this study revealed that their functional diversity does not span the genomic diversity observed in all five clades identified in this study. Our study also found that M. bovis genome harbors a large number of IS elements and their number increases significantly (p = 7.8 × 10⁻⁶) as the genome size increases. Collectively, the genome data and the whole genome-based population analysis in this study may help to develop better understanding of M. bovis induced mycoplasmosis in cattle.

Mycoplasma bovis: Interactions with the Immune System and Failure to Generate an Effective Immune Response

Host responses are often ineffective at clearing Mycoplasma bovis infection and may contribute to the pathogenesis of disease. M bovis possesses a surprisingly large repertoire of strategies to evade and modulate host responses. Unopsonized M bovis impairs phagocytosis and killing by neutrophils and macrophages. Apoptosis of neutrophils and lymphocytes is enhanced, whereas it is delayed in macrophages. Both proinflammatory and antiinflammatory cytokines are stimulated during M bovis infection depending on the cell type and location, and overall systemic responses tend to have a T-helper 2 bias. M bovis reduces proliferation of T cells and, in chronic infection, causes T-cell exhaustion.

GroEL Protein (Heat Shock Protein 60) of Mycoplasma gallisepticum Induces Apoptosis in Host Cells by Interacting with Annexin A2

Mycoplasma gallisepticum is an avian respiratory and reproductive tract pathogen that has a significant economic impact on the poultry industry worldwide. Although membrane proteins of Mycoplasma spp. are thought to play crucial roles in host interactions, very few have had their biochemical function defined. In this study, we found that the GroEL protein (heat shock protein 60) of Mycoplasma gallisepticum could induce apoptosis in peripheral blood mononuclear cells, and the underlying molecular mechanism was further determined. The GroEL gene from Mycoplasma gallisepticum was cloned and expressed in Escherichia coli to facilitate the functional analysis of recombinant protein. The purified GroEL protein was shown to adhere to peripheral blood mononuclear cells (PBMCs) and DF-1 cells and cause apoptosis in PBMCs. A protein pulldown assay coupled with mass spectrometry identified that annexin A2 possibly interacted with GroEL protein. Coimmunoprecipitation assays confirmed that GroEL proteins could bind to annexin A2, and confocal analysis further demonstrated that GroEL colocolized with annexin A2 in HEK293T cells and PBMCs. Moreover, annexin A2 expression was significantly induced by a recombinant GroEL protein in PBMCs, and knocking down annexin A2 expression resulted in significantly reduced apoptosis. Taken together, these data suggest that GroEL induces apoptosis in host cells by interacting with annexin A2, a novel virulence mechanism in Mycoplasma gallisepticum Our findings lead to a better understanding of molecular pathogenesis in Mycoplasma gallisepticum.

Mycoplasma bovis-Induced Inhibition of Bovine Peripheral Blood Mononuclear Cell Proliferation Is Ameliorated after Blocking the Immune-Inhibitory Programmed Death 1 Receptor

Mycoplasma bovis-induced immune suppression is a major obstacle faced by the host for controlling infections. M. bovis impairment of antigen-specific T-cell responses is achieved through inhibiting the proliferation of peripheral blood mononuclear cells (PBMCs). This impairment may contribute to the persistence of M. bovis infection in various sites, including lungs, and its systemic spread to various organs such as joints, with the underlying mechanisms remaining elusive. Here, we elucidated the role of the immune-inhibitory receptor programmed death 1 (PD-1) and its ligand (PD-L1) in M. bovis infection. Flow cytometry (FCM) analyses revealed an upregulation of PD-L1 expression on tracheal and lung epithelial cell lines after M. bovis infection. In addition, we found increased PD-L1 expression on purified lung lavage macrophages following M. bovis infection by FCM and determined its localization by immunofluorescence analysis comparing infected and control lung tissue sections. Moreover, M. bovis infection increased the expression of the PD-1 receptor on total PBMCs and in gated CD4⁺ and CD8⁺ T-cell subpopulations. We demonstrated that M. bovis infection induced a significant decrease in CD4⁺ PD-1^INT and CD8⁺ PD-1^INT subsets with intermediate PD-1 expression, which functioned as progenitor pools giving rise to CD4⁺ PD-1^HIGH and CD8⁺ PD-1^HIGH subsets with high PD-1 expression levels. We blocked PD-1 receptors on PBMCs using anti-PD-1 antibody at the beginning of infection, leading to a significant restoration of the proliferation of PBMCs. Taken together, our data indicate a significant involvement of the PD-1/PD-L1 inhibitory pathway during M. bovis infection and its associated immune exhaustion, culminating in impaired host immune responses.

Improvements in diagnosis of disease caused by Mycoplasma bovis in cattle

The major disease problems associated with Mycoplasma bovis are contagious mastitis and respiratory disease in cattle. Its importance has increased worldwide due to its increasing resistance to antimicrobial agents and the lack of an effective vaccine. Chronically infected silent carriers introduce infection to naïve herds and M. bovis diseases can cause significant economic losses to the affected herds. Availability of a suitable diagnostic tool for extensive screening will improve the ability to determine the appropriate treatment and the full impact of M. bovis in both beef and dairy cattle industries. The present review focuses on the past and present improvements in the diagnosis of disease caused by M. bovis in cattle.

Molecular and Antigenic Characterization of a Mycoplasma Bovis Strain Causing an Outbreak of Infectious Keratoconjunctivitis

An unusually high incidence of infectious keratoconjunctivitis followed by pneumonia and arthritis was observed in beef calves of a managed herd. No Moraxella spp. or bacteria other than Mycoplasma spp. were obtained from conjunctival and nasal swabs. A strategy was designed for characterization of bovine mycoplasmas at species and strain level on the basis of a combination of molecular tools and the immunoblotting method. The strategy made it possible to rapidly assign the bacterium responsible for this outbreak to one of the phylogenetic clusters of bovine mycoplasmas delineated in this study and then to identify it as Mycoplasma bovis. The strain, designated Sar 1, showed a 100% 16S rDNA sequence identity with two European strains (120/81 and MC3386) isolated in Germany and Ireland, respectively, and hosts a vsp gene analog to the vspA, vsp422-4, and vsp422-8 genes of the M. bovis reference strain PG45T and of the field strain 422. The use of a cross-reactive rabbit serum developed against the Mycoplasma agalactiae immunodominant antigen P48 confirmed the molecular findings. The immunological response of calves against M. bovis was also investigated. This is the first report on the occurrence of M. bovis on the Island of Sardinia (Italy).

Mycoplasma bovis isolates recovered from cattle and bison (Bison bison) show differential in vitro effects on PBMC proliferation, alveolar macrophage apoptosis and invasion of epithelial and immune cells

In the last few years, several outbreaks of pneumonia, systemically disseminated infection, and high mortality associated with Mycoplasma bovis (M. bovis) in North American bison (Bison bison) have been reported in Alberta, Manitoba, Saskatchewan, Nebraska, New Mexico, Montana, North Dakota, and Kansas. M. bovis causes Chronic Pneumonia and Polyarthritis Syndrome (CPPS) in young, stressed calves in intensively-managed feedlots. M. bovis is not classified as a primary pathogen in cattle, but in bison it appears to be a primary causative agent with rapid progression of disease with fatal outcomes and an average 20% mature herd mortality. Thus, there is a possibility that M. bovis isolates from cattle and bison differ in their pathogenicity. Hence, we decided to compare selected cattle isolates to several bison isolates obtained from clinical cases. We show differences in modulation of PBMC proliferation, invasion of trachea and lung epithelial cells, along with modulation of apoptosis and survival in alveolar macrophages. We concluded that some bison isolates showed less inhibition of cattle and bison PBMC proliferation, were not able to suppress alveolar macrophage apoptosis as efficiently as cattle isolates, and were more or less invasive than the cattle isolate in various cells. These findings provide evidence about the differential properties of M. bovis isolated from the two species and has helped in the selection of bison isolates for genomic sequencing.

Emerging pathogens of gilthead seabream: characterisation and genomic analysis of novel intracellular β-proteobacteria

New and emerging environmental pathogens pose some of the greatest threats to modern aquaculture, a critical source of food protein globally. As with other intensive farming practices, increasing our understanding of the biology of infections is important to improve animal welfare and husbandry. The gill infection epitheliocystis is increasingly problematic in gilthead seabream (Sparus aurata), a major Mediterranean aquaculture species. Epitheliocystis is generally associated with chlamydial bacteria, yet we were not able to localise chlamydial targets within the major gilthead seabream lesions. Two previously unidentified species within a novel β-proteobacterial genus were instead identified. These co-infecting intracellular bacteria have been characterised using high-resolution imaging and genomics, presenting the most comprehensive study on epitheliocystis agents to date. Draft genomes of the two uncultured species, Ca. Ichthyocystis hellenicum and Ca. Ichthyocystis sparus, have been de novo sequenced and annotated from preserved material. Analysis of the genomes shows a compact core indicating a metabolic dependency on the host, and an accessory genome with an unprecedented number of tandemly arrayed gene families. This study represents a critical insight into novel, emerging fish pathogens and will be used to underpin future investigations into the bacterial origins, and to develop diagnostic and treatment strategies.

Heterologous expression and processing of the flavescence dorée phytoplasma variable membrane protein VmpA in Spiroplasma citri

Background

Flavescence dorée (FD) of grapevine is a phloem bacterial disease that threatens European vineyards. The disease is associated with a non-cultivable mollicute, a phytoplasma that is transmitted by the grapevine leafhopper Scaphoideus titanus in a persistent, propagative manner. The specificity of insect transmission is presumably mediated through interactions between the host tissues and phytoplasma surface proteins comprising the so-called variable membrane proteins (Vmps). Plant spiroplasmas and phytoplasmas share the same ecological niches, the phloem sieve elements of host plants and the hemocoel of insect vectors. Unlike phytoplasmas, however, spiroplasmas, and Spiroplasma citri in particular, can be grown in cell-free media and genetically engineered. As a new approach for studying phytoplasmas-insect cell interactions, we sought to mimic phytoplasmas through the construction of recombinant spiroplasmas exhibiting FD phytoplasma Vmps at the cell surface.

Results

Here, we report the expression of the FD phytoplasma VmpA in S. citri. Transformation of S. citri with plasmid vectors in which the vmpA coding sequence was under the control of the S. citri tuf gene promoter resulted in higher accumulation of VmpA than with the native promoter. Expression of VmpA at the spiroplasma surface was achieved by fusing the vmpA coding sequence to the signal peptide sequence of the S. citri adhesin ScARP3d, as revealed by direct colony immunoblotting and immunogold labelling electron microscopy. Anchoring of VmpA to the spiroplasma membrane was further demonstrated by Triton X-114 protein partitioning and Western immunoblotting. Using the same strategy, the secretion of free, functionally active β-lactamase (used as a model protein) into the culture medium by recombinant spiroplasmas was achieved.

Conclusions

Construction of recombinant spiroplasmas harbouring the FD phytoplasma variable membrane protein VmpA at their surface was achieved, which provides a new biological approach for studying interactions of phytoplasma surface proteins with host cells. Likewise, the secretion of functional β-lactamase by recombinant spiroplasmas established the considerable promise of the S. citri expression system for delivering phytoplasma effector proteins into host cells.

Electronic supplementary material

The online version of this article (doi:10.1186/s12866-015-0417-5) contains supplementary material, which is available to authorized users.

Identification of novel immunogenic proteins from Mycoplasma bovis and establishment of an indirect ELISA based on recombinant E1 beta subunit of the pyruvate dehydrogenase complex

The pathogen Mycoplasma bovis (M. bovis) is a major cause of respiratory disease, mastitis, and arthritis in cattle. Screening the key immunogenic proteins and updating rapid diagnostic techniques are necessary to the prevention and control of M. bovis infection. In this study, 19 highly immunogenic proteins from M. bovis strain PD were identified using 2-dimensional gel electrophoresis, immunoblotting and MALDI-TOF/TOF MS. Of these 19 proteins, pyruvate dehydrogenase E1 component beta subunit (PDHB) showed excellent immune reactivity and repeatability. PDHB was found to be conserved in different M. bovis isolates, as indicated by Western blot analysis. On the basis of these results, a rPDHB-based indirect ELISA (iELISA) was established for the detection of serum antibodies using prokaryotically expressed recombinant PDHB protein as the coating antigen. The specificity analysis result showed that rPDHB-based iELISA did not react with other pathogens assessed in our study except M. agalactiae (which infects sheep and goats). Moreover, 358 serum samples from several disease-affected cattle feedlots were tested using this iELISA system and a commercial kit, which gave positive rates of 50.8% and 39.9%, respectively. The estimated Kappa agreement coefficient between the two methods was 0.783. Notably, 39 positive serum samples that had been missed by the commercial kit were all found to be positive by Western blot analysis. The detection rate of rPDHB-based iELISA was significantly higher than that of the commercial kit at a serum dilution ratio of 1∶5120 to 1∶10,240 (P<0.05). Taken together, these results provide important information regarding the novel immunogenic proteins of M. bovis. The established rPDHB-based iELISA may be suitable for use as a new method of antibody detection in M. bovis.

Mycoplasma mastitis: causes, transmission, and control

Mycoplasma mastitis is an emerging mastitis pathogen. Herd prevalence has increased over the past decade, and this increase parallels the increase in average dairy herd size. It has been documented that the importation of cattle into a herd can result in new cases of Mycoplasma disease in general and Mycoplasma mastitis specifically. Thus, expanding herds are likely to have a greater incidence of this disease. Transmission of the agent can result from either contact with diseased animals or with colonized or asymptomatically infected cattle. Initial transmission might occur via nose-to-nose contact and result in an outbreak of Mycoplasma mastitis, or it might occur during the milking time. This would suggest that new, incoming animals should be quarantined before being comingled with original herd animals. Quarantining does not seem to be a biosecurity strategy often practiced in control of Mycoplasma mastitis and may not be warranted in herds with excellent milking time hygiene practices. The ability to monitor for the incipient stages of an outbreak, often done through bulk tank milk culturing, is recommended.

Mycoplasma agassizii strain variation and distinct host antibody responses explain differences between enzyme-linked immunosorbent assays and Western blot assays

The precarious status of desert (Gopherus agassizii) and gopher (G. polyphemus) tortoises has resulted in conservation efforts that now include health assessment as an important component of management decision-making. Mycoplasmal upper respiratory tract disease (URTD) is one of very few diseases in chelonians for which comprehensive and rigorously validated diagnostic tests exist. In this study, serum samples obtained from eight Gopherus tortoises documented at necropsy to (i) be enzyme-linked immunosorbent assay (ELISA) seropositive using the PS6 antigen, (ii) be infected with Mycoplasma agassizii as indicated by direct isolation of the pathogen from the respiratory surfaces, and (iii) have histological lesions of mycoplasmal URTD were used to evaluate four distinct clinical isolates of M. agassizii as antigens for ELISA and Western blot analyses. Each animal sample reacted in the Western blot with its homologous M. agassizii strain, but recognition of heterologous M. agassizii strains was variable. Further, individual animals varied significantly with respect to the specific proteins recognized by the humoral immune response. An additional 114 Gopherus serum samples were evaluated using ELISA antigens prepared from the four distinct M. agassizii strains; A₄₀₅ values were significantly correlated (r² goodness of fit range, 0.708 to 0.771; P < 0.0001) for all antigens tested. The results confirm that strain variation is responsible for the observed differences between Western blot binding patterns. Thus, reliance on a single M. agassizii strain as an antigen in Western blot assays may provide false-negative results. This could have adverse consequences for the well-being of these environmentally sensitive hosts if false-negative animals were relocated to sites consisting of true-negative populations.

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

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

In situ hybridization for the detection of Mycoplasma bovis in paraffin-embedded lung tissue from experimentally infected calves

Mycoplasma bovis DNA was detected in lung tissue of experimentally infected calves by in situ hybridization (ISH) with a nonradioactive, digoxigenin-labeled DNA probe. The 171-base pair DNA probe targeting part of the gene of the major immunodominant variable surface protein A, which is conserved among all vsp genes, was generated by polymerase chain reaction. Four calves between 57 and 63 days old were inoculated intratracheally with 30 ml of a suspension of M. bovis strain 1067 containing 7 x 10(4) colony forming units per milliliter. Two calves inoculated with 30 ml of sterile medium served as control animals. The calves were euthanized and then examined 21 days after inoculation. The ISH method developed in the current study was suitable for the detection of M. bovis DNA in formalin-fixed, paraffin-embedded lung tissue and may be a valuable tool for diagnostic purposes and for further investigating the pathogenesis of M. bovis infection.

Mycoplasma bovis Infections in young calves

Mycoplasma bovis has emerged as an important pathogen of young intensively reared calves in North America. A variety of clinical diseases are associated with M bovis infections of calves, including respiratory disease, otitis media, arthritis, and some less common presentations. Clinical disease associated with M bovis often is chronic, debilitating, and poorly responsive to antimicrobial therapy. Current control measures are centered on reducing exposure to M bovis through contaminated milk or other sources, and nonspecific control measures to maximize respiratory defenses of the calf. This article focuses on the clinical and epidemiologic aspects of M bovis infections in young calves.

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 antibodies against the Mycoplasma bovis glyceraldehyde-3-phosphate dehydrogenase protein in beef cattle

Diseases caused by Mycoplasma bovis are an important source of financial losses for beef and dairy cattle producers. Antigenic variation in M. bovis hinders the production of effective vaccines and although there are few vaccines available, they are prepared from bacteria obtained from few isolates potentially limiting their effectiveness. Thus, to develop a vaccine that protects against all M. bovis isolates, it is necessary to use a common antigen that shows less or no antigenic variation. We have isolated the gap gene of M. bovis encoding for glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and showed that cattle colonized with M. bovis were able to mount an immune response to GAPDH. Using restriction-fragment length polymorphism (RFLP) of several M. bovis gap genes amplified by PCR, we were able to detect small intragenic variations that allowed us to classify the genes into two groups without changing the antigenic makeup of the proteins. The immune responses detected in cattle combined with the antigenic conservation of the proteins suggest that the M. bovis GAPDH protein could be a potential target for development of a more effective vaccine against all M. bovis isolates.

Characterisation of Mycoplasma capricolum P60 surface lipoprotein and its evaluation in a recombinant ELISA

This paper reports the identification and characterisation of a 60kDa surface protein antigen (P60) of Mycoplasma capricolum subspecies capricolum (Mcc), and describes its diagnostic application. Genomic localization and presence in P60 of conserved functional domains suggested a structural and functional relationship with the immunodominant antigen P48 of Mycoplasma agalactiae, a basic membrane protein. A rP60-ELISA was developed, and it resulted in a high specificity for Mcc infections after evaluation with 125 goat sera. The comparison with an existent ELISA based on whole Mcc cell lysates showed that the two assays have comparable sensitivities, but the rP60-ELISA has the significant advantage of a greater specificity. Results indicate that P60 is a potential marker of Mcc infection, especially useful in areas where the presence of M. capricolum subspecies capripenumoniae is also reported.

Variable lipoprotein genes of Mycoplasma agalactiae are activated in vivo by promoter addition via site-specific DNA inversions

Mycoplasma agalactiae, the etiological agent of contagious agalactia of small ruminants, has a family of related genes (avg genes) which encode surface lipoprotein antigens that undergo phase variation. A series of 13 M. agalactiae clonal isolates, obtained from one chronically infected animal over a period of 7 months, were found to undergo major rearrangement events within the avg genomic locus. We show that these rearrangements regulate the phase-variable expression of individual avg genes. Northern blot analysis and reverse transcription-PCR showed that only one avg gene is transcribed, while the other avg genes are transcriptionally silent. Sequence analysis and primer extension experiments with two M. agalactiae clonal isolates showed that a specific 182-bp avg 5' upstream region (avg-B(2)) that is present as a single chromosomal copy serves as an active promoter and exhibits a high level of homology with the vsp promoter of the bovine pathogen Mycoplasma bovis. PCR analysis showed that each avg gene is associated with the avg-B(2) promoter in a subpopulation of cells that is present in each subclone. Multiple sequence-specific sites for DNA recombination (vis-like), which are presumably recognized by site-specific recombinase, were identified within the conserved avg 5' upstream regions of all avg genes and were found to be identical to the recombination sites of the M. bovis vsp locus. In addition, a gene encoding a member of the integrase family of tyrosine site-specific recombinases was identified adjacent to the variable avg locus. The molecular genetic basis for avg phase-variable expression appears to be mediated by site-specific DNA inversions occurring in vivo that allow activation of a silent avg gene by promoter addition. A model for the control of avg genes is proposed.

Mycoplasma bovis: disease, diagnosis, and control

Mycoplasma bovis is a major, but often overlooked, pathogen causing respiratory disease, mastitis, and arthritis in cattle. It is found worldwide and has spread into new areas, including Ireland and parts of South America, in the last decade. In Europe, it is responsible for at least a quarter to a third of all calf pneumonia although this may be an underestimate as few laboratories regularly monitor for mycoplasmas. Like all mollicutes, M. bovis is inherently refractory to certain groups of antibiotics because it does not possess a cell wall; furthermore evidence is accumulating that strains of M. bovis are becoming resistant to antibiotics, including tetracycline, tilmicosin and spectinomycin, traditionally used for their control. No vaccines are presently available for the control of M. bovis infections.

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.