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

A Systematic Review of the Recent Techniques Commonly Used in the Diagnosis of Mycoplasma bovis in Dairy Cattle

Early detection of Mycoplasmal mastitis is greatly hampered by late seroconversion, slow growth of Mycoplasma organisms, intermittent shedding, and the high cost of diagnostic tests. To improve future diagnostic development, examining the available techniques is necessary. Accordingly, the present study systematically reviewed M. bovis diagnostic studies published between January 2000 and April 2023 utilizing the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) protocol. The protocol registration was performed according to the Open Science Framework (osf.io/ug79h), and the electronic search was conducted in the World Catalog, Mendeley, ProQuest, ScienceDirect, Semantic Scholar, PubMed, Google Scholar, Prime Scholar, and PubMed Central databases using a Boolean operator and inclusion and exclusion criteria. Of the 1194 pieces of literature retrieved, 67 studies were included. Four broad categories of up to 16 diagnostic approaches were reported: microbial culture, serological, DNA-based, and mass spectrometry. Overall, DNA-based techniques were the most published (48.0%), with recombinase polymerase amplification (RPA) and loop-mediated isothermal amplification (LAMP) as the most promising user-friendly, equipment-free techniques. On the other hand, mass spectrometry was reported as the least utilized (2.9%) given the high equipment cost. Though costly and laboratory-allied, DNA-based techniques, particularly PCRs, were reported as the most rapid and specific approach.

Genomic features of Mycoplasma bovis subtypes currently circulating in France

Background

Mycoplasma (M.) bovis is a major etiological agent of bovine respiratory disease, which is the most economically costly disease of cattle worldwide. Cattle disease surveillance on M. bovis is increasingly using gene-based techniques, such as multilocus sequence typing (MLST), or genome-based techniques such as core genome MLST that both require only partial genomic data. However, accurate up-to-date surveillance also demands complete, circular genomes that can be used as reference to track the evolution of the different lineages. Yet, in France, two of the main subtypes currently circulating still have no representing genome in public databases. Here, to address this gap, we provide and compare three new complete M. bovis genomes obtained from recent clinical isolates that represent major subtypes circulating in France and Europe.

Results

Genomes were obtained using a hybrid assembly strategy (Illumina and Nanopore) with fine-tuning of settings and inputs used in the Unicycler assembly pipeline, such as size selection of reads and quality trimming of the FASTQ files. The main characteristics and synteny of the genomes were compared. The three genomes mainly differed by their content in terms of mobile genetic elements, i.e. integrative conjugative elements (ICE) and insertion sequences (IS), a feature that impacts their structure. For instance, strain L15527, representing subtype3 (st3), harbours an exceptionally high number of ICEs, which results in a bigger-sized genome than all those previously described and could be associated with the propensity of st3 to gain and fix mutations through chromosomal transfer mechanisms. In contrast, strain F9160, of st1, is very close to the PG45 type strain isolated in 1961 in the USA, and harbours a huge number of IS. These features may be associated with an evolution towards a host-restricted state or in a “closed” host or environment reservoir until a recent re-emergence.

Conclusions

Whole-genome comparison of the three French M. bovis subtypes provides valuable resources for future studies combining epidemiology, phylogenetic data, and phylodynamic methods.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-022-08818-9.

A novel phage-displayed MilA ELISA for detection of antibodies against Myc. bovis in bovine milk

AIMS

The aim of this study was to assess a phage-displayed MilA protein of Myc. bovis in an indirect ELISA for the detection of Myc. bovis antibodies in milk samples.

METHODS AND RESULTS

The desired sequence of milA gene was synthesized and cloned into pCANTAB-F12 phagemid vector. The expression of the MilA on the phage surface was confirmed by Western blotting. The recombinant phage was used in the development of an indirect ELISA to detect Myc. bovis antibodies in milk samples. There was a significant agreement between the results of phage-based ELISA and recombinant GST-MilA ELISA for the detection of Myc. bovis antibodies in milk samples.

CONCLUSIONS

The inexpensive and convenient phage-based ELISA can be used instead of recombinant protein/peptide ELISA as an initial screening of Myc. bovis-associated mastitis.

SIGNIFICANCE AND IMPACT OF STUDY

Mastitis associated with Myc. bovis is a continuous and serious problem in the dairy industry. Sero-monitoring of Myc. bovis infection cases are one of the key factors for surveillance of the infections in dairy farms. Despite the existence of some commercially serological assays for Myc. bovis antibodies, they have some limitations regarding their sensitivity and availability. The development of accurate diagnosis tools could contribute to control programmes of Myc. bovis-associated mastitis in the dairy herds.

Direct and Rapid Detection of Mycoplasma bovis in Bovine Milk Samples by Recombinase Polymerase Amplification Assays

This study aimed to detetct Mycoplasma bovis (M. bovis) in bovine milk quickly and directly by developing and validating isothermal recombinase polymerase amplification (RPA) assays. Targeting the uvrC gene of M. bovis, an RPA assay based on the fluorescence monitoring (real-time RPA) and an RPA assay combined with a lateral flow strip (LFS RPA) were conducted. It took 20 min for the real-time RPA to finish in a Genie III at 39°C, and 15 min were required to perform the LFS RPA in an incubator block at 39°C, followed by the visualization of the products on the lateral flow strip within 5 min. Both of the two assays showed high specificity for M. bovis without any cross-reaction with the other tested pathogens. With the standard recombinant plasmid pMbovis-uvrC serving as a template, both RPA assays had a limit of detcion of 1.0 × 10¹ copies per reaction, equivalent to that of a real-time PCR assay. In the 65 milk samples collected from cattle with mastitis, the M. bovis genomic DNA was detected in 24 samples by both the real-time RPA and the LFS RPA assays. The developed RPA assays could detect M. bovis in bovine milk in an efficient, convenient, and credible manner as attractive and promising tools, and the assays would be helpful in the rapid response to M. bovis infection causing bovine mastitis.

Expression profiling of microRNAs in the Mycoplasma bovis infected mammary gland tissue in Holstein Friesian cattle

The immune response associated with mastitis caused by Mycoplasma bovis is a very complicated biological process in several type of cells, including immune cells, mammary epithelial cells, and endothelial cells. Thus, revealing of the microRNAs in the Mycoplasma bovis infected mammary gland tissues is particularly important for the immune response mechanism to Mycoplasma bovis. Firstly, 20 mammary gland tissue samples were collected from Holstein Friesian cattle that was located in Erzurum province at 2018 and screened for Mycoplasma bovis. Then, total RNA was isolated from Mycoplasma bovis infected tissues and high-throughput sequencing was performed. After bioinformatics analysis, GO and KEGG analysis of target genes of identified microRNAs were conducted. In this study, a total of 616 microRNAs were found. Our results revealed that 24 of the known microRNAs were expressed differently and 13 of the novel microRNAs were expressed differently in Mycoplasma bovis positive tissues. The target genes of these microRNAs were found to be associated with especially inflammation pathways, including B cell and T cell receptor signaling, Fc gamma R-mediated, phagocytosis/chemokine signaling, and MAPK signaling. In conclusion, this study demonstrated that identified miRNAs may be involved in the signaling pathways during mastitis caused by Mycoplasma bovis.

Extracellular DNA: A Nutritional Trigger of Mycoplasma bovis Cytotoxicity

Microbial access to host nutrients is a key factor of the host-pathogen interplay. With their nearly minimal genome, wall-less bacteria of the class Mollicutes have limited metabolic capacities and largely depend on host nutrients for their survival. Despite these limitations, host-restricted mycoplasmas are widely distributed in nature and many species are pathogenic for humans and animals. Yet, only partial information is available regarding the mechanisms evolved by these minimal pathogens to meet their nutrients and the contribution of these mechanisms to virulence. By using the ruminant pathogen Mycoplasma bovis as a model system, extracellular DNA (eDNA) was identified as a limiting nutrient for mycoplasma proliferation under cell culture conditions. Remarkably, the growth-promoting effect induced by supplementation with eDNA was associated with important cytotoxicity for actively dividing host cells, but not confluent monolayers. To identify biological functions mediating M. bovis cytotoxicity, we produced a library of transposon knockout mutants and identified three critical genomic regions whose disruption was associated with a non-cytopathic phenotype. The coding sequences (CDS) disrupted in these regions pointed towards pyruvate metabolism as contributing to M. bovis cytotoxicity. Hydrogen peroxide was found responsible for eDNA-mediated M. bovis cytotoxicity, and non-cytopathic mutants were unable to produce this toxic metabolic compound. In our experimental conditions, no contact between M. bovis and host cells was required for cytotoxicity. Further analyses revealed important intra-species differences in eDNA-mediated cytotoxicity and H₂O₂ production, with some strains displaying a cytopathic phenotype despite no H₂O₂ production. Interestingly, the genome of strains PG45 and HB0801 were characterized by the occurrence of insertion sequences (IS) at close proximity to several CDSs found disrupted in non-cytopathic mutants. Since PG45 and HB0801 produced no or limited amount of H₂O₂, IS-elements might influence H₂O₂ production in M. bovis. These results confirm the multifaceted role of eDNA in microbial communities and further identify this ubiquitous material as a nutritional trigger of M. bovis cytotoxicity. M. bovis may thus take advantage of the multiple sources of eDNA in vivo to modulate its interaction with host cells, a way for this minimal pathogen to overcome its limited coding capacity.

A longitudinal observational study of the dynamics of Mycoplasma bovis antibodies in naturally exposed and diseased dairy cows

Mycoplasma bovis is an important pathogen causing disease and substantial economic losses in cattle. However, knowledge of the dynamics of antibody responses in individual cows in the face of an outbreak is currently extremely limited. The use of commercial antibody tests to support clinical decision-making and for surveillance purposes is therefore challenging. Our objective was to describe the dynamics of M. bovis antibody responses in 4 Danish dairy herds experiencing an acute outbreak of M. bovis-associated disease, and to compare the antibody dynamics between dairy cows with different disease manifestations. A total of 120 cows were examined using a standardized clinical protocol and categorized into 4 disease groups: "mastitis," "systemic," "nonspecific," and "none." Paired blood and milk samples were collected and tested using a commercial M. bovis antibody-detecting ELISA. Plots of raw data and generalized additive mixed models with cow and herd as random effects were used to describe serum and milk antibody dynamics relative to the estimated time of onset of clinical disease. Cows with mastitis had high optical density measurement (ODC%) of antibodies in both milk and serum at disease onset. The estimated mean ODC% in milk was below the manufacturer's cut-off for the other groups for the entire study period. The estimated mean serum ODC% in the "systemic" group was high at onset of disease and stayed above the cut-off until 65 d after disease onset. However, the lower 95% confidence interval (CI) for the mean ODC% was only above the manufacturer's cut-off between 7 and 17 d after onset of disease. The CI of the "systemic" and "none" groups did not overlap at any time between the day of disease onset and 65 d after disease onset, and the estimated mean ODC% for both the "nonspecific" and "none" groups were generally below the cut-off for the majority of the study period. In conclusion, the serum antibody responses were highly dynamic and showed a high level of variation between individual cows. This strongly suggests that serology is unlikely to be useful for individual diagnosis of M. bovis-associated disease in dairy cows. However, it might still be useful for herd- or group-level diagnosis. Antibodies in milk were only increased in cows with M. bovis mastitis, indicating that milk antibody measurements only have diagnostic utility for cows with mastitis.

A review of mycoplasma diagnostics in cattle

Mycoplasma species have a global distribution causing serious diseases in cattle worldwide including mastitis, arthritis, pneumonia, otitis media and reproductive disorders. Mycoplasma species are typically highly contagious, are capable of causing severe disease, and are difficult infections to resolve requiring rapid and accurate diagnosis to prevent and control disease outbreaks. This review discusses the development and use of different diagnostic methods to identify Mycoplasma species relevant to cattle, with a particular focus on Mycoplasma bovis. Traditionally, the identification and diagnosis of mycoplasma has been performed via microbial culture. More recently, the use of polymerase chain reaction to detect Mycoplasma species from various bovine samples has increased. Polymerase chain reaction has a higher efficiency, specificity, and sensitivity for laboratory diagnosis when compared with conventional culture‐based methods. Several tools are now available for typing Mycoplasma spp. isolates, allowing for genetic characterization in disease outbreak investigations. Serological diagnosis through the use of indirect ELISA allows the detection of antimycoplasma antibodies in sera and milk, with their use demonstrated on individual animal samples as well as BTM samples. While each testing method has strengths and limitations, their combined use provides complementary information, which when interpreted in conjunction with clinical signs and herd history, facilitates pathogen detection, and characterization of the disease status of cattle populations.

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.

A serologic survey of Mycoplasma spp. in farmed bison ( Bison bison) herds in western Canada

Mycoplasma bovis is emerging as an important pathogen of farmed bison in North America and is associated with high morbidity and mortality in affected herds. We developed an in-house ELISA to detect antibodies against Mycoplasma spp. in bison sera. The aims of the study were to estimate the seroprevalence against Mycoplasma spp. in bison herds with or without past history of M. bovis-associated disease, and to determine potential risk factors for seropositivity to Mycoplasma spp. in farmed bison in western Canada. A total of 858 serum samples were collected from bison >1 y of age from 19 bison herds. The individual and herd-level seroprevalence of Mycoplasma spp. was 12% and 79%, respectively. The proportion of seropositive animals was 0-41% and 0-9% for herds with or without a history of M. bovis-associated disease, respectively. Mycoplasma spp. appear to be widespread in bison in Manitoba, Saskatchewan, and Alberta. Eight of 11 herds with no history of M. bovis-associated disease were seropositive for Mycoplasma spp., which suggests that bison can be subclinically infected with Mycoplasma spp., or that infection may be underdiagnosed. Although not specific to M. bovis, the in-house ELISA developed to detect antibodies against Mycoplasma spp. may prove to be a valuable herd-level screening tool, providing insight needed for the development of appropriate prevention and control measures for Mycoplasma-related disease in bison herds.

Development of a direct competitive ELISA for the detection of Mycoplasma bovis infection based on a monoclonal antibody of P48 protein

Background

Mycoplasma bovis (M. bovis) is a major, but often overlooked, pathogen documented to cause respiratory disease, mastitis, and arthritis in cattle throughout China since 2008. Here, we report the development of a direct competitive enzyme-linked immunosorbent assay (Dc-ELISA) to detect M. bovis antibody.

Results

We used a recombinant P48 protein and monoclonal antibody (mAb) 10E. MAb 10E, prepared against the recombinant P48 protein of M. bovis, identified all M. bovis strains with no cross-reactivity with other related pathogens. Coating micro plates with P48 protein instead of whole M. bovis cells as well as the use of mAb 10E produced a specific and sensitive Dc-ELISA for M. bovis antibody detection with a cut-off percent inhibition (PI) value of 32%. Compared with two commercial indirect ELISA (i-ELISA) kits, our Dc-ELISA offered a higher positive detection rate in 165 clinical bovine serum samples.

Conclusions

A rapid, sensitive, and reliable serological diagnosis method was developed for M. bovis, which can facilitate M. bovis surveillance, assisting researchers in understanding the ecology and epidemiology of M. bovis.

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.

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.

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.

The role of Mycoplasma bovis in bovine respiratory disease outbreaks in veal calf feedlots

To assess the prevalence and relative importance of Mycoplasma bovis among the pathological agents implicated in bovine respiratory disease (BRD), we surveyed 135 veal calves from nine feedlots in eastern France during naturally occurring outbreaks of respiratory disease. Occurrence of respiratory pathogens, M. bovis, bovine viral diarrhoea (BVD) virus, bovine respiratory syncytial (BRS) virus and parainfluenza-3 (PI3) virus was investigated by seroconversion and isolation of bacteria and viruses from broncho-alveolar fluids. M. bovis and pathogenic respiratory bacteria were isolated in eight of the nine feedlots, and from 106 and 32, respectively, of the 135 tested animals. Seroconversion to PI3 virus occurred in four lots. BVD and BRS viruses were detected in eight and one lot, respectively. M. bovis was the most frequently isolated aetiologic agent in these BRD outbreaks, spreading early and widely throughout the affected units (60-100% rate of isolation and seroconversion). These results stress the importance of M. bovis in the BRD complex.

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.

Genetic and antigenic characterization of the surface lipoprotein P48 of Mycoplasma bovis

The presence of a membrane lipoprotein homologous to the P48 of Mycoplasma agalactiae was investigated in different Mycoplasma bovis isolates selected by geographical locations and biological properties. Its potential as a diagnostic tool was also discussed. The presence of a specific signal observed in all M. bovis field isolates probed with a rabbit antiserum raised against the M. agalactiae recombinant P48 demonstrated that this protein is structurally and antigenically conserved within the M. bovis cluster. No signal was detected when testing six different mycoplasma species found in cattle. The p48 gene was identified by PCR approach and partially sequenced. Full length gene sequence was obtained by direct bacterial chromosome sequencing. Five UGAs were selectively mutated into UGG and the full length mutated gene, lacking the signal peptide, was cloned and expressed in Escherichia coli. The purified recombinant antigen (r-P48) was evaluated as a potential marker of infection using a panel of 86 well-characterized sera from experimentally and naturally infected cattle. Specific IgM antibodies were detected within 6-9 days after experimental infection followed by an IgG response lasting from the third/fourth week after contact. Although antibody titers were well below those observed in sheep or goats infected with M. agalactiae, results suggest that M. bovis r-P48 can be used as a specific marker of infection.

Examination of the role of Mycoplasma bovis in bovine pneumonia and a mathematical model for its evaluation

The authors screened 34 large cattle herds for the presence of Mycoplasma bovis infection by examining slaughtered cattle for macroscopic lung lesions, by culturing M. bovis from lung lesions and at the same time by testing sera for the presence of antibodies against M. bovis. Among the 595 cattle examined, 33.9% had pneumonic lesions, mycoplasmas were isolated from 59.9% of pneumonic lung samples, and 10.9% of sera from those animals contained antibodies to M. bovis. In 25.2% of the cases M. bovis was isolated from lungs with no macroscopic lesions. The proportion of seropositive herds was 64.7%. The average seropositivity rate of individuals was 11.3% but in certain herds it exceeded 50%. A probability model was developed for examining the relationship among the occurrence of pneumonia, the isolation of M. bovis from the lungs and the presence of M. bovis specific antibodies in sera.