Status of the development of a vaccine against Mycoplasma bovis

Investigation of the safety and protective efficacy of an attenuated and marker M. bovis-BoHV-1 combined vaccine in bovines

Bovine respiratory disease (BRD) is one of the most common diseases in the cattle industry worldwide; it is caused by multiple bacterial or viral coinfections, of which Mycoplasma bovis (M. bovis) and bovine herpesvirus type 1 (BoHV-1) are the most notable pathogens. Although live vaccines have demonstrated better efficacy against BRD induced by both pathogens, there are no combined live and marker vaccines. Therefore, we developed an attenuated and marker M. bovis-BoHV-1 combined vaccine based on the M. bovis HB150 and BoHV-1 gG-/tk- strain previously constructed in our lab and evaluated in rabbits. This study aimed to further evaluate its safety and protective efficacy in cattle using different antigen ratios. After immunization, all vaccinated cattle had a normal rectal temperature and mental status without respiratory symptoms. CD4+, CD8+, and CD19+ cells significantly increased in immunized cattle and induced higher humoral and cellular immune responses, and the expression of key cytokines such as IL-4, IL-12, TNF-α, and IFN-γ can be promoted after vaccination. The 1.0 × 108 CFU of M. bovis HB150 and 1.0 × 106 TCID50 BoHV-1 gG-/tk- combined strain elicited the most antibodies while significantly increasing IgG and cellular immunity after challenge. In conclusion, the M. bovis HB150 and BoHV-1 gG-/tk- combined strain was clinically safe and protective in calves; the mix of 1.0 × 108 CFU of M. bovis HB150 and 1.0 × 106 TCID50 BoHV-1 gG-/tk- strain was most promising due to its low amount of shedding and highest humoral and cellular immune responses compared with others. This study introduces an M. bovis-BoHV-1 combined vaccine for application in the cattle industry.

Prevalence and antimicrobial susceptibility of Mycoplasma bovis from the upper and lower respiratory tracts of healthy feedlot cattle and those diagnosed with bovine respiratory disease

Mycoplasma bovis is an important respiratory pathogen of cattle. In this study, the prevalence and antimicrobial susceptibility of M. bovis were evaluated from two Cohorts of feedlot cattle spanning an 8-year period. In the first study conducted in 2008-2009, nasopharyngeal swabs from cattle sampled at feedlot entry and after 60 days on feed were collected (Cohort 1). In a second study conducted in 2015-2016, nasopharyngeal and trans-tracheal samples were collected from cattle diagnosed with bovine respiratory disease (BRD) and matching healthy controls (Cohort 2). For Cohort 1, the prevalence of M. bovis was lower in cattle at entry compared to when the same individuals were sampled ≥60 days later (P < 0.05). For Cohort 2, the prevalence of M. bovis was greater in both nasopharyngeal and tracheal samples from cattle diagnosed with BRD, compared to controls (P < 0.05). In both Cohorts, almost all isolates were resistant to tilmicosin. Compared to M. bovis from Cohort 1, isolates of Cohort 2 exhibited increased resistance to clindamycin, enrofloxacin, florfenicol, tylosin, and tulathromycin, with the latter showing resistance levels >90 %. These data suggest that antimicrobials used to prevent and treat BRD selected for resistance in M. bovis over the 8-year period. For macrolides, cross-resistance occurred and M. bovis can retain resistance even when antimicrobial selection pressure is removed. Within 9 years of commercial availability of tulathromycin, the majority of M. bovis displayed resistance. Therefore, longitudinal evaluation of resistance in respiratory pathogens is important to ensure efficacious treatment of BRD.

Transmission of Mycoplasma bovis infection in bovine in vitro embryo production

Mycoplasma bovis (M. bovis) causes several costly diseases in cattle and has a negative effect on cattle welfare. There is no effective commercial vaccine, and antimicrobial resistance is common. Maintaining a closed herd is the best method to minimize the risk of introduction of M. bovis. Assisted reproduction is crucial in a closed herd to make genetic improvements. M. bovis has been found in commercial semen, and contaminated semen has been the source of disease in naïve dairy herds. The objective of this study was to evaluate M. bovis transmission in bovine in vitro embryo production (IVP) using several possible exposure routes. We used a wild-type M. bovis strain isolated from semen at a final concentration of 10⁶ CFU/mL to infect cumulus-oocyte complexes, spermatozoa, and 5-day-old embryos. We also used naturally contaminated semen in fertilization. Blastocysts were collected on day 7-8 and zona pellucida (ZP)-intact embryos were either washed 12 times, including trypsin washes as recommended by the International Embryo Technology Society (IETS), or left unwashed. Washed and unwashed embryos, follicular fluids, maturation medium, cumulus cells, fertilization medium, and G1 and G2 culture media, as well as all wash media were analyzed using enrichment culture followed by real-time PCR detection of M. bovis. Altogether, 76 pools containing 363 unwashed embryos and 52 pools containing 261 IETS washed embryos were analyzed after oocytes, spermatozoa, or 5-day-old embryos were infected with M. bovis or naturally contaminated semen was used in fertilization. We could not detect M. bovis in any of the embryo pools. M. bovis was not found in any of 12 wash media from different exposure experiments. M. bovis did not affect the blastocyst rate, except when using experimentally infected semen. Contrary to an earlier study, which used a cell co-culture system, we could not demonstrate M. bovis in embryo wash media or tight adherence of M. bovis to ZP-intact embryos. Naturally infected semen did not transmit M. bovis to embryos. We conclude that by using our IVP system, the risk of M. bovis transmission via IVP embryos to recipient cows is very low.

Mycoplasma Bovis adhesins and their target proteins

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

Herd-level prevalence of Mycoplasma bovis in Swedish dairy herds determined by antibody ELISA and PCR on bulk tank milk and herd characteristics associated with seropositivity

Mycoplasma bovis is an important pathogen causing pneumonia, mastitis, and arthritis in cattle, leading to reduced animal welfare and economic losses worldwide. In this cross-sectional study, we investigated the prevalence of M. bovis in bulk tank milk (BTM) and herd characteristics associated with a positive antibody test result in Swedish dairy herds. Bulk tank milk samples from all Swedish dairy herds (n = 3,144) were collected and analyzed with ID Screen antibody ELISA and PCR. Information on herd characteristics was collected from the national Dairy Herd Improvement database. To identify herd characteristics associated with the presence of antibodies in BTM, logistic regression was used in 4 different models. The apparent herd-level prevalence of M. bovis infection based on antibodies in BTM was 4.8%, with large regional differences ranging from 0 to 20%. None of the BTM samples was positive by PCR. All the antibody-positive herds were situated in the south of Sweden. The logistic regression model showed that larger herds had higher odds of detectable antibodies in BTM (herd size >120 cows, odds ratio = 8.8). An association was also found between antibodies in BTM and both a higher late calf mortality (2-6 mo) and a higher young stock mortality (6-15 mo). This study showed a clear regional difference in the apparent prevalence of M. bovis infection based on antibodies. The relatively low prevalence of M. bovis in Sweden is a strong motivator for the cattle industry to take steps to prevent further spread of the infection. It is essential that the M. bovis status of free herds be known, and the regional differences shown in this study suggest that testing is highly recommended when live cattle from high-prevalence areas are being introduced into herds. We do not recommend using PCR on BTM to detect infected herds, owing to the low detection frequency in this study.

Transcriptomic Responses of Mycoplasma bovis Upon Treatments of trans-Cinnamaldehyde, Carvacrol, and Eugenol

Mycoplasma bovis (M. bovis) is an insidious, wall-less primary bacterial pathogen that causes bovine pneumonia, mid-ear infection, mastitis, and arthritis. The economic losses caused by M. bovis due to culling, diminished milk production, and feed conversion are underestimated because of poor diagnosis/recognition. Treatment with common antibiotics targeting the cell wall is ineffective. Plant-derived antimicrobials (PDAs) such as food-grade trans-cinnamaldehyde (TC), eugenol (EU), and carvacrol (CAR) are inexpensive and generally regarded as safe for humans and animals yet possess strong anti-bacterial properties. In preliminary studies, we found that all three PDAs inhibited the growth of M. bovis in vitro. Through RNA sequencing, we report here that CAR affected the expression of 153 genes which included the downregulation of energy generation-related proteins, pentose phosphate pathway, and upregulation of ribosomes and translation-related proteins. Few differentially expressed genes were found when M. bovis was treated with TC, EU, or when the three PDAs were double or triple combined. Our results suggest that, as opposed to the effect of CAR, the growth-inhibitory effects of TC and EU at levels tested may be exerted through mechanisms other than gene expression regulations.

A genetic toolkit and gene switches to limit Mycoplasma growth for biosafety applications

Mycoplasmas have exceptionally streamlined genomes and are strongly adapted to their many hosts, which provide them with essential nutrients. Owing to their relative genomic simplicity, Mycoplasmas have been used to develop chassis for biotechnological applications. However, the dearth of robust and precise toolkits for genomic manipulation and tight regulation has hindered any substantial advance. Herein we describe the construction of a robust genetic toolkit for M. pneumoniae, and its successful deployment to engineer synthetic gene switches that control and limit Mycoplasma growth, for biosafety containment applications. We found these synthetic gene circuits to be stable and robust in the long-term, in the context of a minimal cell. With this work, we lay a foundation to develop viable and robust biosafety systems to exploit a synthetic Mycoplasma chassis for live attenuated vectors for therapeutic applications.

Mycoplasmas are minimal cell model organisms but lack genetic tools. Here the authors provide a robust genetic toolkit for Mycoplasma demonstrating gene circuit engineering applications.

Flow cytometric analysis of bronchoalveolar lavage fluid immune dynamics in calves

Understanding the immune dynamics in the respiratory mucosa of calves is necessary for a good management of bovine respiratory disease. Immune dynamics in the respiratory mucosa in humans and experimental animals has been assessed by flow cytometric analysis of bronchoalveolar lavage fluid (BALF); however, few reports have addressed this subject in calves. The aim of this study was to establish a universal method to analyze bronchoalveolar lavage fluid (BALF) by flow cytometry and to obtain basic knowledge of bovine respiratory mucosal immune dynamics. We investigated the immune cell populations in BALF and evaluated the surface antigen expression of alveolar macrophages in calves using flow cytometer. To further analyze the surface antigen variation observed in alveolar macrophages in detail, stimulation assays were performed in vitro. BALF cells were separated into three distinct populations based on their light scatter plot, which were considered to be macrophages, lymphocytes, and neutrophils. In most individuals, most of the BALF immune cells were alveolar macrophages, but an increased proportion of lymphocytes and neutrophils was observed in some individuals. Analysis of each surface antigen expression in alveolar macrophages showed that CD21 and MHC class II expression changed in response to changes in the leukocyte population. Moreover, when alveolar macrophages were stimulated with interferon-γ in vitro, the expression of CD21 was drastically reduced and MHC class II was increased, suggesting that functional changes in alveolar macrophages themselves are involved in the immune dynamics.

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.

Integrating the Human and Animal Sides of Mycoplasmas Resistance to Antimicrobials

Mycoplasma infections are frequent in humans, as well as in a broad range of animals. However, antimicrobial treatment options are limited, partly due to the lack of a cell wall in these peculiar bacteria. Both veterinary and human medicines are facing increasing resistance prevalence for the most commonly used drugs, despite different usage practices. To date, very few reviews have integrated knowledge on resistance to antimicrobials in humans and animals, the latest dating back to 2014. To fill this gap, we examined, in parallel, antimicrobial usage, resistance mechanisms and either phenotype or genotype-based methods for antimicrobial susceptibility testing, as well as epidemiology of resistance of the most clinically relevant human and animal mycoplasma species. This review unveiled common features and differences that need to be taken into consideration in a "One Health" perspective. Lastly, two examples of critical cases of multiple drug resistance are highlighted, namely, the human M. genitalium and the animal M. bovis species, both of which can lead to the threat of untreatable infections.

Suitability of Nasal and Deep Nasopharyngeal Swab Sampling of Calves in the Mycoplasma bovis Control Program

Mycoplasma bovis is an important cattle pathogen affecting animal health, welfare, and productivity. The main disease syndromes are mastitis, pneumonia, and otitis media in young stock, as well as arthritis. Response to antibiotic treatment is poor and no effective vaccine is available. Asymptomatic carriers are common and usually harbor the organism in the airways or mammary glands. Purchase of carrier animals is a major risk for the introduction of infection into naive herds. Following the detection of M. bovis in Finland in 2012, a voluntary control program was established. It aims to prevent the spread of the infection and to help farms attain certification of a low M. bovis risk. Among the diagnostic tools in the program, nasal swabs (NS) from young calves have been tested for M. bovis to indicate the infection status of the herd. In this study, we assessed the suitability of this test method. We analyzed the effectiveness of NS and deep nasopharyngeal swabs (NP) to detect M. bovis in pneumonic and healthy calves in dairy herds recently infected with M. bovis. In pneumonic calves, NP sampling followed by culture and real-time PCR demonstrated a proportion of positive agreement (PPA) of 0.91 compared with bronchoalveolar lavage (BAL), whereas NS showed only 0.5 PPA compared with BAL. Among healthy dairy calves, overall M. bovis prevalence in NS was 29.6%. The highest rate of shedding (43%) occurred in calves 31–60 days old. At the calf level, M. bovis prevalence in NP samples was 47% compared with 33% in NS samples among the 284 studied calves. However, at the herd level, NS sampling classified 51 out of 54 herds with a positive infection status as infected, whereas in NP sampling, the respective figure was 43 out of 54 herds (p = 0.061). In conclusion, NS sampling from calves under 6 months of age and analyzed by real-time PCR is a cost-efficient method for a control program to detect M. bovis in dairy herds, even if no M. bovis mastitis has been detected in the herd. For pneumonic calves, we recommend only NP or BAL sampling.

Protection against Mycoplasma bovis infection in calves following intranasal vaccination with modified-live Mannheimia haemolytica expressing Mycoplasma antigens

Novel live vaccine strains of Mannheimia haemolytica serotypes (St)1 and St6, expressing and secreting inactive yet immunogenic leukotoxin (leukotoxoid) fused to antigenic domains of Mycoplasma bovis Elongation Factor Tu (EFTu) and Heat shock protein (Hsp) 70 were constructed and tested for efficacy in cattle. Control calves were administered an intranasal mixture of M. haemolytica St1 and St6 mutants (ΔlktCAV4) expressing and secreting leukotoxoid while vaccinated calves were administered an intranasal mixture of like M. haemolytica St1 and St6 leukotoxoid mutants coupled to M. bovis antigens (EFTu-Hsp70-ΔlktCAV4). Both M. haemolytica strains were recovered from palatine tonsils up to 34 days post intranasal exposure. On day 35 all calves were exposed to bovine herpes virus-1, four days later lung challenged with virulent M. bovis, then euthanized up to 20 days post-challenge. Results showed all cattle produced systemic antibody responses against M. haemolytica. The vaccinates also produced systemic antibody responses to M. bovis antigen, and concurrent reductions in temperatures, middle ear infections, joint infection and lung lesions versus the control group. Notably, dramatically decreased lung loads of M. bovis were detected in the vaccinated cattle. These observations indicate that the attenuated M. haemolytica vaccine strains expressing Mycoplasma antigens can control M. bovis infection and disease symptoms in a controlled setting.

Addressing the Antimicrobial Resistance of Ruminant Mycoplasmas Using a Clinical Surveillance Network

Antimicrobial resistance (AMR) surveillance of mycoplasmas of veterinary importance has been held back for years due to lack of harmonized methods for antimicrobial susceptibility testing (AST) and interpretative criteria, resulting in a crucial shortage of data. To address AMR in ruminant mycoplasmas, we mobilized a long-established clinical surveillance network called "Vigimyc." Here we describe our surveillance strategy and detail the results obtained during a 2-year monitoring period. We also assess how far our system complies with current guidelines on AMR surveillance and how it could serve to build epidemiological cut-off values (ECOFFs), as a first attainable criterion to help harmonize monitoring efforts and move forward to clinical breakpoints. Clinical surveillance through Vigimyc enables continuous collection, identification and preservation of Mycoplasma spp. isolates along with metadata. The most frequent pathogens, i.e., M. bovis and species belonging to M. mycoides group, show stable clinicoepidemiological trends and were included for annual AST. In the absence of interpretative criteria for ruminant mycoplasmas, we compared yearly minimum inhibitory concentration (MIC) results against reference datasets. We also ran a SWOT (Strengths, Weaknesses, Opportunities, Threats) analysis on the overall service provided by our AMR surveillance strategy. Results of the 2018-2019 surveillance campaign were consistent with the reference datasets, with M. bovis isolates showing high MIC values for all antimicrobial classes except fluoroquinolones, and species of the Mycoides group showing predominantly low MIC values. A few new AMR patterns were detected, such as M. bovis with lower spectinomycin MICs. Our reference dataset partially complied with European Committee on Antimicrobial Susceptibility Testing (EUCAST) requirements, and we were able to propose tentative epidemiological cut-off values (TECOFFs) for M. bovis with tilmicosin and spectinomycin and for M. mycoides group with tilmicosin and lincomycin. These TECOFFs were consistent with other published data and the clinical breakpoints of Pasteurellaceae, which are often used as surrogates for mycoplasmas. SWOT analysis highlighted the benefit of pairing clinical and antimicrobial resistance surveillance despite the AST method-related gaps that remain. The international community should now direct efforts toward AST method harmonization and clinical interpretation.

Importance and Antimicrobial Resistance of Mycoplasma bovis in Clinical Respiratory Disease in Feedlot Calves

Simple Summary

Bovine respiratory disease is a common health and economic problem that mainly affects calves raised in feedlots. Several viruses and bacteria may be involved, but Mycoplasma bovis can cause disease chronification and poor response to antimicrobial treatment. This study investigated the role of Mycoplasma bovis in cases of clinical respiratory disease unresponsive to treatment that affected feedlot calves in southeast Spain, and tested the in vitro susceptibility of a selection of isolates to the specific set of antimicrobials used for therapy in vivo. Mycoplasma bovis was found in 86.9% (20/23) of the calves, predominantly in the lungs (78.26%; 18/23) where it was involved in pulmonary lesions. Furthermore, the selected isolates were found to be resistant in vitro to most of the antimicrobials specifically used for treating the animals in vivo. These results highlight the implication of Mycoplasma bovis in the bovine respiratory disease affecting feedlot calves in Spain.

Abstract

Bovine respiratory disease (BRD) is an important viral and/or bacterial disease that mainly affects feedlot calves. The involvement of Mycoplasma bovis in BRD can lead to chronic pneumonia poorly responsive to antimicrobial treatment. Caseonecrotic bronchopneumonia is a pulmonary lesion typically associated with M. bovis. In Spain, M. bovis is widely distributed in the feedlots and circulating isolates are resistant to most antimicrobials in vitro. However, the role of this species in clinical respiratory disease of feedlot calves remains unknown. Furthermore, available data are relative to a fixed panel of antimicrobials commonly used to treat BRD, but not to the specific set of antimicrobials that have been used for treating each animal. This study examined 23 feedlot calves raised in southeast Spain (2016–2019) with clinical signs of respiratory disease unresponsive to treatment. The presence of M. bovis was investigated through bacteriology (culture and subsequent PCR), histopathology and immunohistochemistry. The pathogen was found in 86.9% (20/23) of the calves, mainly in the lungs (78.26%; 18/23). Immunohistochemistry revealed M. bovis antigens in 73.9% (17/23) of the calves in which caseonecrotic bronchopneumonia was the most frequent lesion (16/17). Minimum inhibitory concentration assays confirmed the resistance of a selection of 12 isolates to most of the antimicrobials specifically used for treating the animals in vivo. These results stress the importance of M. bovis in the BRD affecting feedlot calves in Spain.

Epidemiological Survey of Mycoplasma bovis in Yaks on the Qinghai Tibetan Plateau, China

Mycoplasma bovis (M. bovis) is one of the most important pneumonia pathogens in yaks. It may result in more economic losses due to the cold and anoxia condition at Qinghai Tibetan plateau. However, to date, limited information on M. bovis infection in yaks is available in China. For this purpose, the seroprevalence of M. bovis was investigated in yaks living in the mentioned area through commercial ELISA kits. A total of 959 yaks were incorporated into this study. The prevalence of the disease in yaks was 48.70%. The serological results revealed a relatively high prevalence of M. bovis infection in yaks. The present study may greatly contribute to the prevention of this disease. More importance should be given to the potential threat caused by M. bovis in the special plateau.

Proposal of an iELISA for Mycoplasma bovis diagnosis in dairy cattle and associated risk factors

ABSTRACT Mycoplasma bovis is a highly contagious agent associated with several pathologies in cattle. The detection of reactive antibodies to M. bovis by Indirect Enzyme-Linked Immunosorbent Assay (iELISA) identifies if there was an exposure to the microorganism. The current study aimed to optimize an iELISA from M. bovis total cell antigen, applying it to bovine serum samples, and to evaluate risk factors. Serum samples were obtained from 400 cows from 17 herds from Southeast Brazil. In the optimization of iELISA, the following was established: 2 μg/mL of antigen, sera dilution 1:300, and conjugate dilution 1:15000. The frequency was 62.3% (249/400) of reactive animals and 100% (17/17) of reactive herds. Risk factors were: herds with more than 100 animals (OR= 3.1; CI= 95%); Holstein breed (OR= 72.5; CI= 95%); cows (OR= 29.7; CI= 95%); intensive breeding system (OR= 3.3; CI= 95%); associated small ruminant production (OR= 4.4; CI= 95%); milk production above 500L (OR= 2.9; CI= 95%); no quarantine (OR= 1.5; CI= 95%); mechanical milking (OR= 5.5; CI= 95%) and cases of mastitis (OR= 5.5; CI= 95%). The proposed iELISA was able to detect antibodies reactive to M. bovis in bovine serum. Knowledge of these risk factors can assist in the implementation of prophylactic measures.

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

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

Mycoplasma bovis in Nordic European Countries: Emergence and Dominance of a New Clone

Mycoplasma (M.) bovis is an important pathogen of cattle implicated in a broad range of clinical manifestations that adversely impacts livestock production worldwide. In the absence of a safe, effective commercial vaccine in Europe, the reported reduced susceptibility to antimicrobials for this organism has contributed to difficulties in controlling infection. Despite global presence, some countries have only recently experienced outbreaks of this pathogen. In the present study, M. bovis isolates collected in Denmark between 1981 and 2016 were characterized to determine (i) genetic diversity and phylogenetic relationships using whole genome sequencing and various sequence-based typing methods and (ii) patterns of antimicrobial resistance compared to other European isolates. The M. bovis population in Denmark was found to be highly homogeneous genomically and with respect to the antimicrobial resistance profile. Previously dominated by an old genotype shared by many other countries (ST17 in the PubMLST legacy scheme), a new predominant type represented by ST94-adh1 has emerged. The same clone is also found in Sweden and Finland, where M. bovis introduction is more recent. Although retrieved from the Netherlands, it appears absent from France, two countries with a long history of M. bovis infection where the M. bovis population is more diverse.

Efficacy of Two Antibiotic-Extender Combinations on Mycoplasma bovis in Bovine Semen Production

Mycoplasma bovis is an important bovine pathogen. Artificial insemination (AI) using contaminated semen can introduce the agent into a naïve herd. Antibiotics, most often gentamycin, tylosin, lincomycin, spectinomycin (GTLS) combination are added to semen extender to prevent transmission of pathogenic bacteria and mycoplasmas. In a commercial AI straw production system with industrial scale procedures, we analyzed the mycoplasmacidal efficacy of GTLS and ofloxacin on M. bovis ATCC and wild type strain isolated from commercial AI straws. The strains were spiked at two concentrations (10⁶ and 10³ CFU/mL) into semen. Viable M. bovis in frozen semen straws was detected by enrichment culture and real-time PCR. We also compared different protocols to extract M. bovis DNA from spiked semen. None of the antibiotic protocols had any effect on the viability of either of the M. bovis strains at high spiking concentration. At low concentration, the wild type was inhibited by all other protocols, except low GTLS, whereas the ATCC strain was inhibited only by high GTLS. The InstaGene™ matrix was the most effective method to extract M. bovis DNA from semen. When there is a low M. bovis contamination level in semen, GTLS used at high concentrations, in accordance with Certified Semen Services requirements, is more efficient than GTLS used at concentrations stated in the OIE Terrestrial Code.

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.

Persistence in Livestock Mycoplasmas—a Key Role in Infection and Pathogenesis

Purpose of Review

Mycoplasma, economically important pathogens in livestock, often establishes immunologically complex persistent infections that drive their pathogenesis and complicate prophylaxis and therapy of the caused diseases. In this review, we summarize some of the recent findings concerning cellular and molecular persistence mechanisms related to the pathogenesis of mycoplasma infections in livestock.

Recent Findings

Data from recent studies prove several mechanisms including intracellular lifestyle, immune dysregulation, and autoimmunity as well as microcolony and biofilm formation and apoptosis of different host cell types as important persistence mechanisms in several clinically significant Mycoplasma species, i.e., M. bovis, M. gallisepticum, M. hyopneumoniae, and M. suis.

Summary

Evasion of the immune system and the establishment of persistent infections are key features in the pathogenesis of livestock mycoplasmas. In-depth knowledge of the underlying mechanisms will provide the basis for the development of therapy and prophylaxis strategies against mycoplasma infections.

Mycoplasma bovis in Spanish Cattle Herds: Two Groups of Multiresistant Isolates Predominate, with One Remaining Susceptible to Fluoroquinolones

Mycoplasma bovis is an important bovine pathogen causing pneumonia, mastitis, and arthritis and is responsible for major economic losses worldwide. In the absence of an efficient vaccine, control of M. bovis infections mainly relies on antimicrobial treatments, but resistance is reported in an increasing number of countries. To address the situation in Spain, M. bovis was searched in 436 samples collected from beef and dairy cattle (2016–2019) and 28% were positive. Single-locus typing using polC sequences further revealed that two subtypes ST2 and ST3, circulate in Spain both in beef and dairy cattle, regardless of the regions or the clinical signs. Monitoring of ST2 and ST3 isolates minimum inhibitory concentration (MIC) to a panel of antimicrobials revealed one major difference when using fluoroquinolones (FQL): ST2 is more susceptible than ST3. Accordingly, whole-genome sequencing (WGS) further identified mutations in the gyrA and parC regions, encoding quinolone resistance-determining regions (QRDR) only in ST3 isolates. This situation shows the capacity of ST3 to accumulate mutations in QRDR and might reflect the selective pressure imposed by the extensive use of these antimicrobials. MIC values and detection of mutations by WGS also showed that most Spanish isolates are resistant to macrolides, lincosamides, and tetracyclines. Valnemulin was the only one effective, at least in vitro, against both STs.

Pathogenesis and Virulence of Mycoplasma bovis

Mycoplasma bovis is an important component of the bovine respiratory disease complex and recent reports identified that other species are also affected by M bovis. Control of the disease caused by M bovis has been unsuccessful owing to many factors, including the capacity of M bovis to evade and modulate the immune system of the host; the lack of known virulence factors; the absence of a cell wall, which renders antibiotics targeting cell-wall synthesis unusable; and the failure of vaccines to control disease on the field. The current knowledge on virulence and pathogenesis is presented in this review.

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.

Antibodies Specific to Membrane Proteins Are Effective in Complement-Mediated Killing of Mycoplasma bovis

The metabolic inhibition (MI) test is a classic test for the identification of mycoplasmas, used for measuring the growth-inhibiting antibodies directed against acid-producing mycoplasmas, although their mechanism still remains obscure. To determine the major antigens involved in the immune killing of Mycoplasma bovis, we used a pulldown assay with anti-M. bovis antibodies as bait and identified nine major antigens.

The metabolic inhibition (MI) test is a classic test for the identification of mycoplasmas, used for measuring the growth-inhibiting antibodies directed against acid-producing mycoplasmas, although their mechanism still remains obscure. To determine the major antigens involved in the immune killing of Mycoplasma bovis, we used a pulldown assay with anti-M. bovis antibodies as bait and identified nine major antigens. Among these antigens, we performed the MI test and determined that the growth of M. bovis could be inhibited effectively in the presence of complement by antibodies against specifically membrane protein P81 or UgpB in the presence of complement. Using a complement killing assay, we demonstrated that M. bovis can be killed directly by complement and that antibody-dependent complement-mediated killing is more effective than that by complement alone. Complement lysis and scanning electron microscopy results revealed M. bovis rupture in the presence of complement. Together, these results suggest that the metabolic inhibition of M. bovis is antibody-dependent complement-mediated killing. This study provides new insights into mycoplasma killing by the complement system and may guide future vaccine development studies for the treatment of mycoplasma infection. Furthermore, our findings also indicate that mycoplasmas may be an appropriate new model for studying the lytic activity of membrane attack complex (MAC).

iTRAQ-based proteomic analysis of Mycoplasma bovis NM-28 strain from two generations for vaccine screening

Mycoplasma bovis is an important pathogenic bacterium affecting cows and cattle. Clinically, an inactivated vaccine of M. bovis is mainly used to prevent infection by this bacterium. The changes that occur in the antigen when M. bovis is continuously passaged in vitro remain unknown. Therefore, we performed an in vitro serial passage of the M. bovis NM-28 strain, which was isolated and identified in our laboratory. An isobaric tags for relative and absolute quantitation (iTRAQ)-based quantitative proteomics method was used to analyse the differences between generations 3 and 60. Many major membrane proteins or protective antigens reported in the literature did not exhibit changes between these generations. We found an imbalance between growth rate and nutrition in the 60th generation. The proteomics results were verified by western blotting and real-time PCR. Growth curves were also prepared based on colony-forming units (CFUs) between the 3rd and 60th generations. The number of colonies in the 60th generation in the stationary phase was 5 × 10⁹ CFU mL^-1, which was 10-fold higher than that in the 3rd generation. The 60th generation of the NM-28 strain can be used as an inactivated vaccine strain of M. bovis to lower production costs compared to use of the 3rd generation.

A European inter-laboratory trial to evaluate the performance of three serological methods for diagnosis of Mycoplasma bovis infection in cattle using latent class analysis

Background

Mycoplasma bovis (M. bovis) is an emerging bovine pathogen, leading to significant economic losses in the livestock industry worldwide. Infection can result in a variety of clinical signs, such as arthritis, pneumonia, mastitis and keratoconjunctivitis, none of which are M. bovis-specific. Laboratory diagnosis is therefore important. Serological tests to detect M. bovis antibodies is considered an effective indicator of infection in a herd and often used as a herd test. Combined with clinical judgement, it can also be used to implement control strategies and/or to estimate the disease prevalence within a country. However, due to lack of harmonisation of approaches to testing, and serological tests used by different laboratories, comparisons of prevalence data between countries is often difficult. A network of researchers from six European countries designed and participated in an inter-laboratory trial, with the aim of evaluating the sensitivity (Se) and specificity (Sp) of two commercially available ELISA tests (ID Screen® ELISA (IDvet) and BIO K302 ELISA (BIO-X Diagnostics)) for diagnosis of M. bovis infection. Each laboratory received a blinded panel of bovine sera and tested independently, according to manufacturer’s instructions. Western blot analyses (WB) performed by one of the participating laboratories was used as a third diagnostic test in the statistical evaluation of Se and Sp values using latent class analysis.

Results

The Se of WB, the ID Screen® ELISA and the BIO K302 ELISA were determined to be 91.8, 93.5 and 49.1% respectively, and corresponding Sp of the three tests were 99.6, 98.6 and 89.6%, respectively.

Conclusions

The present study is, to our knowledge, the first to present an inter-laboratory comparison of the BIO K302 ELISA and the ID Screen® ELISA. Based on our results, the ID Screen® ELISA showed high consistency with WB and performed with higher precision and accuracy than the BIO K302 ELISA.

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.

Characterisation of the course of Mycoplasma bovis infection in naturally infected dairy herds

Mycoplasma bovis causes bovine respiratory disease, mastitis, arthritis and otitis. The importance of M. bovis has escalated because of recent outbreaks and introductions into countries previously free of M. bovis. We characterized the course of M. bovis infection on 19 recently infected dairy farms over 24 months. Our objective was to identify diagnostic tools to assess the efficacy of control measures to assess low risk infection status on M. bovis infected farms. PCR assays and culture were used to detect M. bovis, and in-house and BioX ELISAs were used to follow antibody responses. Cows and young stock were sampled on four separate occasions, and clinical cases were sampled when they arose. On 17 farms, a few cases of clinical mastitis were detected, mostly within the first eight weeks after the index case. Antibodies detected by in-house ELISA persisted in the serum of cows at least for 1.5 years on all farms, regardless of the M. bovis infection status or signs of clinical disease or subclinical mastitis on the farm. Six out of 19 farms became low risk as the infection was resolved. Our results suggest that, for biosecurity purposes, regular monitoring should be conducted on herds by screening for M. bovis in samples from cows with clinical mastitis and calves with pneumonia, in conjunction with testing young stock by screening longitudinally collected nasal swabs for M. bovis and sequential serum samples for antibody against recombinant antigen.

Bovine Epithelial in vitro Infection Models for Mycoplasma bovis

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

Mycoplasma bovis investigations in cattle

This article was prepared by Anne Ridley, Lead of the APHA Mycoplasma Team, and Gareth Hateley, Veterinary Lead of the APHA Cattle Expert Group.

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

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

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

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