Mycoplasma bovis real-time polymerase chain reaction assay validation and diagnostic performance

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.

Pathogenicity and molecular characterization of Mycoplasma bovis isolate from calves in Morocco

Bovine respiratory disease caused by Mycoplasma bovis (M. bovis) represents a major health problem for cattle worldwide that causes considerable financial losses. This study reports for the first time the molecular and pathogenic characterization of a strain of M. bovis isolated from a dead local calf with respiratory symptoms in Morocco. M. bovis was isolated from lung tissue, purified by cloning, and subtyped using MLST analysis. Experimental infection was conducted in naïve calves to evaluate pathogenicity. The isolate was identified as a new subtype ST-204 that shares similarities with the 2019-2021 Spanish strains (ST-169, ST-170, ST-171) and the 2018 Algeria isolate (ST-4). Experimental infection resulted in fever and respiratory symptoms with serous nasal discharge. At postmortem, lung lesions of congestion and hepatization were observed with lymph node enlargement and foci of necrosis. The study confirms the high pathogenicity of the isolate and the important role of M. bovis in bovine respiratory disease.

Mycoplasma bovis testing for the screening of semen imported into New Zealand

AIMS

To evaluate the fitness of three PCR assays for the detection of Mycoplasma bovis in dilute (extended) bovine semen, and a reverse transcriptase-PCR (RT-PCR) adaptation as a proxy for viability.

MATERIALS AND METHODS

Four commercial kit-based methods for nucleic acid extraction were compared to test for the presence of PCR inhibitors in nucleic acid extracted from undiluted and diluted semen. Then, analytical sensitivity, analytical specificity, and diagnostic specificity of two real-time PCR and one conventional PCR were evaluated for the detection of M. bovis DNA in semen and compared against microbial culture. Furthermore, an RT-PCR was adapted to detect RNA only and tested on viable and non-viable M. bovis to establish its ability to discriminate between the two.

RESULTS

No significant PCR inhibition was detected from the dilute semen. All DNA extraction methods except one were equivalent, regardless of semen dilution. The analytical sensitivity of the real-time PCR assays was estimated as 45.6 cfu per 200 µL semen straw (2.2 × 10² cfu/mL). The conventional PCR was 10 times less sensitive. No cross-reactivity was observed for the real-time PCR for any of the bacteria tested and the diagnostic specificity was estimated as 100 (95% CI = 94.04-100) %. The RT-PCR was poor in distinguishing between viable and non-viable M. bovis. The mean quantification cycle (Cq) values for RNA extracted from different treatments to kill M. bovis remained unchanged 0-48 hours after inactivation.

CONCLUSION AND CLINICAL RELEVANCE

The real-time PCR were fit for the purpose of screening dilute semen for the detection of M. bovis to prevent incursion via importation of infected semen. The real-time PCR assays can be used interchangeably. The RT-PCR could not reliably indicate the viability of M. bovis. Based on the results from this study, a protocol and guidelines have been produced for laboratories elsewhere that wish to test bovine semen for M. bovis.

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.

Development of a multiplex qPCR assay for the simultaneous detection of Mycoplasma bovis, Mycoplasma species, and Acholeplasma laidlawii in milk

Contagious bovine mastitis caused by Mycoplasma bovis and other Mycoplasma species including Mycoplasma californicum, Mycoplasma bovigenitalium, Mycoplasma alkalescens, Mycoplasma arginini, and Mycoplasma canadense is an economical obstacle affecting many dairy herds throughout California and elsewhere. Routine bacteriological culture-based assays for the pathogens are slow and subject to false-positive results due to the presence of the related, non-pathogenic species Acholeplasma laidlawii. To address the need for rapid and accurate detection methods, a new TaqMan multiplex, quantitative real-time PCR (qPCR) assay was developed that targets the 16S rRNA gene of Mycoplasma, rpoB gene of M. bovis, and the 16S to 23S rRNA intergenic transcribed spacer (ITS) region of A. laidlawii. qPCR amplification efficiency and range of detection were similar for individual assays in multiplex as when performed separately. The multiplex assay was able to distinguish between M. bovis and A. laidlawii as well as detect Mycoplasma spp. collectively, including Mycoplasma californicum, Mycoplasma bovigenitalium, Mycoplasma canadense, Mycoplasma arginini and Mycoplasma alkalescens. In milk, the lower limit of detection of M. bovis, M. californicum, and A. laidlawii with the multiplex assay was between 120 to 250 colony forming units (CFU) per mL. The assay was also able to simultaneously detect both M. bovis and A. laidlawii in milk when present in moderate (103 to 104 CFU/mL) to high (106 to 107 CFU/mL) quantities. Compared to laboratory culture-based methods, the multiplex qPCR diagnostic specificity (Sp) was 100% (95% CI [86.8-100]; n = 26) and diagnostic sensitivity (Se) was 92.3% (95% CI [74.9-99.1]; n = 26) for Mycoplasma species in milk samples collected from California dairy farms. Similarly, the Sp was 100% (95% CI [90.5-100]; n = 37) and Se was 93.3% (95% CI [68.1-99.8]; n = 15) for M. bovis. Our assay can detect and distinguish among M. bovis, other prevalent Mycoplasma spp., and non-pathogenic Acholeplasma laidlawii for effective identification and control of mycoplasma mastitis, ultimately supporting dairy cattle health and high-quality dairy products in California.

Prevalence of Mycoplasma spp. in the Respiratory Tract of Healthy North American Bison (Bison bison) and Comparison with Serum Antibody Status

Mycoplasma bovis is a primary cause of respiratory and reproductive diseases in North American bison (Bison bison), with significant morbidity and mortality. The epidemiology of M. bovis in bison is poorly understood, hindering efforts to develop effective control measures. Our study considered whether healthy bison might be carriers of M. bovis, potentially serving as unrecognized sources of exposure. We used culture and PCR to identify mycoplasmas in the nasal cavity or tonsil of 499 healthy bison from 13 herds and two abattoirs in the US and Canada. Mycobacterium bovis was detected in 15 bison (3.0%) representing two herds in the US and one in Canada, while M. bovirhinis, M. bovoculi, M. arginini, or M. dispar was identified from an additional 155 bison (31.1%). Mycoplasma bovirhinis was identified most frequently, in 142 bison (28.5%) representing at least 10 herds. Of the 381 bison for which serum was available, only 6/13 positive for M. bovis (46.2%) tested positively with an M. bovis ELISA, as did 19/368 negative for M. bovis (5.2%). Our data reveal that M. bovis can be carried in the upper respiratory tract of healthy bison with no prior history or clinical signs of mycoplasmosis and that a large proportion of carriers may not produce detectable antibodies. Whether carriage of other mycoplasmas can trigger cross-reactive antibodies that may confound M. bovis serology requires further study.

MALDI-TOF mass spectrometry and high-resolution melting PCR for the identification of Mycoplasma bovis isolates

BACKGROUND

Mycoplasma bovis is an important pathogen of cattle worldwide. Many different clinical manifestations of infection can occur, including respiratory disease, arthritis, and mastitis, causing heavy losses to beef and dairy industries. Because Mycoplasma species are slow-growing and fastidious, traditional identification methods are not cost- or time-effective, and improved methods are sought to streamline laboratory processes. High-resolution melting PCR (HRM-PCR) and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) are 2 relatively recent tools that are rapid and inexpensive to use; we tested 9 isolates of M. bovis using both assays. The HRM-PCR assay used universal mycoplasma primers for the 16S-23S intergenic spacer region (IGSR).

RESULTS

The resulting melting profiles of the field isolates were indistinguishable from the reference strain, indicating accurate identification. For the MALDI-TOF MS, each M. bovis isolate was accurately identified. Mycoplasma arginini and Mycoplasma alkalescens isolates did not identify as M. bovis when tested by either assay.

CONCLUSIONS

Our work shows that either assay could be used to identify unknown M. bovis isolates. For future work, the MALDI-TOF MS library should be expanded to include more mycoplasmas, and the HRM-PCR assay should be tested on additional mycoplasmas to ensure that the melting profiles are sufficiently distinctive.

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.

Molecular genetic techniques and oligonucleotides for mycoplasma identification – a review

Control of distribution of mycoplasmal infections in cattle herds is essential in the majority of countries world-wide. Various PCR procedures are available to detect mycoplasmas in cell cultures and bovine mycoplasma in different types of samples. We reviewed some common PCR techniques and specific primers targeted to different bacterial genetic regions of mycoplasma. Several researchers used the same PCR approach and Mycoplasma spp. as a target but their results could not be compared because different primer pairs were used. These methods and primers were first developed to identify mycoplasma species that contaminate animal cell cultures, and then were used by other researchers to differentiate mycoplasmas as a cow infecting agent. Our analysis of the specificity of these primer pairs to nucleotide sequences of five Mycoplasma spp. showed that oligonucleotides have less specificity to them. Numerous commercially available PCR kits are applicable to find mycoplasma contamination in cell cultures and fewer of them can be used in veterinary diagnostics. Although serological and culture techniques are still used, it is necessary to develop a new multiplex PCR technique with a more specific primer set especially in agrarian countries.

Complete Genome Sequences of 16 Mycoplasma bovis Isolates from Canadian Bison and Cattle

Here, we report the complete genome sequences of 12 Mycoplasma bovis isolates cultured from Canadian bison and 4 cultured from Canadian cattle. The sequences are of value for understanding the phylogenetic relationship between cattle and bison isolates and will aid in elucidating the genetic basis for virulence and host specificity.

Here, we report the complete genome sequences of 12 Mycoplasma bovis isolates cultured from Canadian bison and 4 cultured from Canadian cattle. The sequences are of value for understanding the phylogenetic relationship between cattle and bison isolates and will aid in elucidating the genetic basis for virulence and host specificity.

Whole dairy herd sampling to detect subclinical intramammary Mycoplasma bovis infection after clinical mastitis outbreaks

After clinical Mycoplasma bovis mastitis outbreaks in dairy herds, M. bovis can persist as subclinical intramammary infections. Identification and culling of sub-clinically infected cows may be warranted to reduce future pathogen transmission and disease. In this study, apparent cow-level prevalences of M. bovis intramammary infection within 4 milking herds immediately following outbreaks of clinical disease due to M. bovis were determined utilising PCR and culture. All clinically affected M. bovis cows had been culled from the herds prior to herd sampling. Composite milk samples were collected once from each cow (n = 2,258) using a routine milk recording sampling technique. These samples were pooled for PCR screening; positive pools were analysed in different sized pools as needed from large to small, until individual PCR-positive animals could be identified. Despite M. bovis seroprevalences of 76% (herd 1), 40% (herd 2), 20% (herd 3) and 16% (herd 4), apparent prevalences of intramammary infection in the main milking group based on PCR in herds 1 to 4 were 0.2% (1/497), 0.0% (0/475), 0.1% (1/816) and 0.0% (0/444), respectively. Due to the low apparent prevalences of subclinical intramammary mycoplasma infections in these herds and the high expense associated with milk sample collection and testing, the return on diagnostic investment was very limited, particularly considering that additional cows are likely to have been colonised with mycoplasma in other anatomical sites. The results of this study suggest that pursuing identification of cows with subclinical intramammary mycoplasma infections following resolution of clinical M. bovis disease outbreaks in dairy herds may be of minimal benefit in programs designed to control or eradicate M. bovis.

Microbiological and molecular detection of Mycoplasma bovis in milk samples from bovine clinical mastitis

ABSTRACT: The genus Mycoplasma includes more than 200 bacterial species that cause disease in animals. It is responsible for causing mastitis in bovines and may be related to other manifestations, such as arthritis and pneumonia in calves and heifers. The present study aimed to detect Mycoplasma bovis isolated from milk samples of bovine clinical mastitis, and to compare the isolation rates in two culture media: Hayflick and SP4. An initial screening was performed in order to detect the presence of the class Mollicutes in 1166 milk samples from clinical mastitis by the conventional Polymerase Chain Reaction (PCR) technique. According to the 1166 milk samples evaluated, 8.6% (100/1166) were positive to class Mollicutes. Regarding molecular analyses, 1.1% (13/1166) of conventional PCR for positive M. bovis was obtained and 0.9% (11/1166) in real-time PCR. The results of the microbiological culture of the 100 samples previously screened demonstrated that 6% (6/100) of colony growth have been developed when using the Hayflick medium, and 11% (11/100) when using the SP4 medium (including the positive on Hayflick medium). Concerning the 11 isolates obtained in the microbiological culture, conventional PCR confirmed M. bovis in nine of them, and two cultures were negative. In the phylogenetic analysis of the isolates, all of them were grouped in M. bovis and M. agalactiae clusters. The results confirmed the importance of the presence of M. bovis in the etiology of bovine clinical mastitis and reinforced the need for further studies to elucidate other Mycoplasma species that may be involved in bovine clinical mastitis in Brazil.

A direct qPCR screening approach to improve the efficiency of Mycoplasma bovis isolation in the frame of a broad surveillance study

Culturing Mycoplasma bovis is laborious and unpredictable with most laboratories relying on molecular methods for its detection and identification. However, bacterial culture is still necessary to relate phenotypic characteristics to genotypic traits within and between individual strains. Thus, the main objective of this study was to develop a procedure that saved time and consumables during the culturing of M. bovis within the scope of a broad antimicrobial resistance surveillance project. Deep nasopharyngeal swabs (DNPS) collected from feedlot cattle upon arrival at 10 Southern Alberta feedlots were enriched in broth and an aliquot of the culture was directly used in a M. bovis-specific quantitative PCR (qPCR) assay. Only qPCR-positive cultures were plated onto agar media for the isolation of M. bovis. The detection of M. bovis from broth culture by direct-culture-qPCR proved to be more sensitive (1.61 × 10² CFU/mL) than using a commercial kit (1.61 × 10³ CFU/mL) to extract DNA from pure cultures of M. bovis. When isolation of M. bovis from broth-enriched DNPS (n = 208 samples) was used as the gold standard for diagnostics, the qPCR screening approach showed 100% sensitivity, 87.27% specificity, and a kappa index = 0.87 (strong agreement). In contrast, qPCR of DNPS samples (n = 58) exhibited 100% sensitivity, 42.86% specificity, and a kappa index = 0.49 (weak agreement). The qPCR protocol described here together with a high throughput direct-culture-qPCR approach for sample testing made it possible to reduce the labor and cost of M. bovis isolation by eliminating the need to process 97.3% of M. bovis-negative samples. This was possible through the use of qPCR Ct values as a predictive tool of the likelihood of M. bovis isolation. This new procedure could be evaluated for its use in antimicrobial resistance surveillance programs that focus on Mycoplasma species.

The pulmonary virome, bacteriological and histopathological findings in bovine respiratory disease from western Canada

The aetiology and pathogenesis of bovine respiratory disease (BRD) are complex and involve the interplay of infectious agents, management and environmental factors. Previous studies of BRD focused on ante‐mortem samples from the upper respiratory tract and identified several unconventional viruses. The lung, however, is the primary location where significant BRD lesions are usually found and is a common post‐mortem diagnostic specimen. In this study, results of high‐throughput virome sequencing, bacterial culture, targeted real‐time PCR and histological examination of 130 bovine pneumonic lungs from western Canadian cattle were combined to explore associations of microorganisms with different types of pneumonia. Fibrinous bronchopneumonia (FBP) was the predominant type of pneumonia (46.2%, 60/130) and was associated with the detection of Mannheimia haemolytica. Detection of Histophilus somni and Pasteurella multocida was associated with suppurative bronchopneumonia (SBP) and concurrent bronchopneumonia and bronchointerstitial pneumonia (BP&BIP), respectively. Sixteen viruses were identified, of which bovine parvovirus 2 (BPV2) was the most prevalent (11.5%, 15/130) followed by ungulate tetraparvovirus 1 (UTPV1, 8.5%, 11/130) and bovine respiratory syncytial virus (BRSV, 8.5%, 11/130). None of these viruses, however, were significantly associated with a particular type of pneumonia. Unconventional viruses such as influenza D virus (IDV) and bovine rhinitis B virus (BRBV) were detected, although sparsely, consistent with our previous findings in upper respiratory tract samples. Taken together, our results show that while virus detection in post‐mortem lung samples is of relatively little diagnostic value, the strong associations of H. somni and M. haemolytica with SBP and FBP, respectively, indicate that histopathology can be useful in differentiating bacterial aetiologies.

Coinfection of Swiss cattle with bovine parainfluenza virus 3 and Mycoplasma bovis at acute and chronic stages of bovine respiratory disease complex

Viral agents such as bovine respiratory syncytial virus (BRSV) and bovine parainfluenza virus 3 (BPIV-3) are considered primary infectious agents in bovine respiratory disease complex (BRDC). Information regarding the pathogenesis of BRDC is scarce, especially at an advanced chronicity stage, in addition to ongoing coinfection with other primary agents such as Mycoplasma bovis. Based on a retrospective review of histology slides from 104 autopsy cases, we classified cases according to type of pneumonia and chronicity. We performed immunohistochemistry (IHC) for BRSV, BPIV-3, and M. bovis as well as real-time PCR (rtPCR) for M. bovis on lung tissue of all 104 cases and correlated results with the morphologic type of pneumonia. Histomorphologically, 79 cases were classified as bronchopneumonia, 16 as bronchointerstitial pneumonia, and 9 as interstitial pneumonia. In 89 cases, at least 1 of the investigated agents was detected by IHC; 44 of these cases had a coinfection. BPIV-3 was the predominant agent present, as a single infection in 39 cases, and in coinfection with M. bovis in 39 cases. Comparing the detection methods for M. bovis, rtPCR was more specific and sensitive than IHC. The combination of both methods provided a good visual tool for assessing severity and distribution of M. bovis antigen within the tissue. Unlike BRSV, BPIV-3 and M. bovis persisted in chronic BRDC, suggesting ongoing impairment of defense mechanisms in the lung.

Optimizing identification of Mycoplasma bovis by MALDI-TOF MS

Fast and accurate identification of Mycoplasma bovis in cattle samples is of great importance for rational treatment and control of pneumonia, arthritis and mastitis. However, which growth conditions will allow the fastest identification of M. bovis with MALDI-TOF MS remains unclear. Therefore, growth conditions and incubation time were investigated to optimize identification of M. bovis with MALDI-TOF MS and an in-house library was constructed. Nine different M. bovis strains were inoculated in triplicate in three liquid media (B1-3). Basic broth (B1) consisted of pleuropneumonia-like organism broth, enriched with 25% horse serum and 0.7% yeast extract. B2 and B3 were additionally supplemented with 0.5% pyruvate or 520 μg/mL ampicillin, respectively. Protein extraction was performed after 24, 48, 72, 96 and 120 h of incubation (37 °C, 5% CO₂) and processed with Autoflex III smartbeam. Identification scores ≥1.7 were interpreted as reliable. The present study showed reliable identification of M. bovis with MALDI-TOF MS as early as 24 h after inoculation, and in broth supplemented with pyruvate, up to 120 h after inoculation. Serial dilutions showed improved survival of M. bovis in broth with pyruvate. The addition of ampicillin to prevent contamination, did not impair identification of M. bovis and state-of-the-art in-house libraries contributed to higher identification scores for M. bovis with MALDI-TOF MS.

A European interlaboratory trial to evaluate the performance of different PCR methods for Mycoplasma bovis diagnosis

BACKGROUND

Several species-specific PCR assays, based on a variety of target genes are currently used in the diagnosis of Mycoplasma bovis infections in cattle herds with respiratory diseases and/or mastitis. With this diversity of methods, and the development of new methods and formats, regular performance comparisons are required to ascertain diagnostic quality. The present study compares PCR methods that are currently used in six national veterinary institutes across Europe. Three different sample panels were compiled and analysed to assess the analytical specificity, analytical sensitivity and comparability of the different PCR methods. The results were also compared, when appropriate, to those obtained through isolation by culture. The sensitivity and comparability panels were composed of samples from bronchoalveolar fluids of veal calves, artificially contaminated or naturally infected, and hence the comparison of the different methods included the whole workflow from DNA extraction to PCR analysis.

RESULTS

The participating laboratories used i) five different DNA extraction methods, ii) seven different real-time and/or end-point PCRs targeting four different genes and iii) six different real-time PCR platforms. Only one commercial kit was assessed; all other PCR assays were in-house tests adapted from published methods. The analytical specificity of the different PCR methods was comparable except for one laboratory where Mycoplasma agalactiae was tested positive. Frequently, weak-positive results with Ct values between 37 and 40 were obtained for non-target Mycoplasma strains. The limit of detection (LOD) varied from 10 to 10³ CFU/ml to 10³ and 10⁶ CFU/ml for the real-time and end-point assays, respectively. Cultures were also shown to detect concentrations down to 10² CFU/ml. Although Ct values showed considerable variation with naturally infected samples, both between laboratories and tests, the final result interpretation of the samples (positive versus negative) was essentially the same between the different laboratories.

CONCLUSION

With a few exceptions, all methods used routinely in the participating laboratories showed comparable performance, which assures the quality of diagnosis, despite the multiplicity of the methods.

Development of duplex fluorescence-based loop-mediated isothermal amplification assay for detection of Mycoplasma bovis and bovine herpes virus 1

Mycoplasma bovis (MB) and bovine herpes virus 1 (BHV-1) are two important pathogens that cause bovine respiratory disease in the beef feedlot and dairy industries. The aim of this study was to develop and validate a duplex fluorescence-based loop-mediated isothermal amplification (DLAMP) assay for simultaneous detection of MB and BHV-1. Two sets of specific primers for each pathogen were designed to target the unique sequences of the MB uvrC gene and the BHV-1 gB gene. The inner primer for BHV-1 was synthesized with the fluorophore FAM at the 5' end to detect the BHV-1 gB gene, and the inner primer for MB was synthesized with the fluorophore CY5 at the 5' end to detect the MB uvrC gene. The DLAMP reaction conditions were optimized for rapid and specific detection of MB and BHV-1. The DLAMP assay developed here could specifically detect MB and BHV-1 without cross-reaction with other known non-target bovine pathogens. The sensitivity of this DLAMP assay was as low as 2 × 10² copies for recombinant plasmids containing the MB and BHV-1 target genes. In a detection test of 125 clinical samples, the positive rates for MB, BHV-1 and co-infection were 44.8%, 13.6% and 1.6%, respectively. Furthermore, the sensitivity and specificity of DLAMP were determined as 95%-96.6% and 100%, respectively, of those of field sample detection by the real-time polymerase chain reaction (PCR) assay recommended by the World Organisation for Animal Health. Overall, DLAMP provides a rapid, sensitive and specific assay for the identification of MB and BHV-1 in clinical specimens and for epidemiological surveillance.

Relative virulence in bison and cattle of bison-associated genotypes of Mycoplasma bovis

Mycoplasma bovis, a frequent contributor to polymicrobial respiratory disease in cattle, has recently emerged as a major health problem in North American bison. Strong circumstantial evidence suggests it can be the sole pathogen causing disease manifestations in outbreaks of mortality in bison, but direct evidence is lacking. The goal of this study was to compare clinical signs and lesions in bison and cattle experimentally infected with field isolates of M. bovis recovered from bison. Bison (n = 7) and cattle (n = 6), seronegative for anti-M. bovis IgG, were exposed intranasally to M. bovis and necropsied 4-6 weeks later. Blood and nasal swabs were collected on day 0 (before exposure), day 11 and at necropsy. Samples of lung, lymph node, liver and spleen were also collected at necropsy. The only clinical sign observed was an elevation in the core body temperature of bison during the first few weeks post-exposure. Grossly visible lesions were apparent at necropsy in the lungs of five bison and the lymph node of one bison, while none were evident in cattle. Histologic evaluation revealed moderate to severe pulmonary lesions in four bison but none in cattle. M. bovis was recovered from tissues demonstrating gross lesions and from the lymph nodes of one additional bison and two cattle. All animals seroconverted by the time of necropsy. These data provide the first direct evidence that M. bovis can be a sole or primary cause of respiratory disease in healthy bison, although the isolates used were unable to cause disease in healthy cattle.

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.

Mistaken identity of an open reading frame proposed for PCR-based identification of Mycoplasma bovis and the effect of polymorphisms and insertions on assay performance

Mycoplasma bovis is an important cause of disease in cattle and bison. Because the bacterium requires specialized growth conditions, many diagnostic laboratories routinely use PCR to replace or complement conventional isolation and identification methods. A frequently used target of such assays is the uvrC gene, which has been shown to be highly conserved among isolates. We discovered that a previously described PCR putatively targeting the uvrC gene amplifies a fragment from an adjacent gene predicted to encode a lipoprotein. Comparison of the lipoprotein gene sequence from 211 isolates revealed several single nucleotide polymorphisms, 1 of which falls within a primer-binding sequence. Additionally, 3 isolates from this group were found to have a 1,658-bp transposase gene insertion within the amplified region that leads to a false-negative result. The insertion was not detected in a further 164 isolates. We found no evidence that the nucleotide substitution within the primer-binding region affects the assay sensitivity, performance, or limit of detection. Nonetheless, laboratories utilizing this method for identification of M. bovis should be aware that the region amplified may be prone to nucleotide substitutions and/or insertions relative to the sequence used for its design and that occasional false-negative results may be obtained.

Development of real-time PCR assay for the detection of Mycoplasma bovis

Mycoplasma bovis is one of the important bovine mycoplasma involved in economically important clinical conditions like respiratory diseases, otitis media, and mastitis. The present study was undertaken with the objective of developing a SYBR Green dye-based real-time PCR assay targeting uvrC gene for the diagnosis of M. bovis. The analytical sensitivity and specificity of the assay were evaluated. The test showed 10³-fold more sensitivity than conventional PCR and detected down to 100 fg level of DNA. It was found to be specific, as no cross reactivity was shown with other related bacteria and Mycoplasma species. The developed assay was able to detect down to 40 copies of uvrC gene from spiked bovine milk samples. At present, this developed assay may be used as a valuable diagnostic tool for the detection of Mycoplasma bovis.

Comparison of culture and a multiplex probe PCR for identifying Mycoplasma species in bovine milk, semen and swab samples

Mycoplasma spp. are a major cause of mastitis, arthritis and pneumonia in cattle, and have been associated with reproductive disorders in cows. While culture is the traditional method of identification the use of PCR has become more common. Several investigators have developed PCR protocols to detect M. bovis in milk, yet few studies have evaluated other sample types or other important Mycoplasma species. Therefore the objective of this study was to develop a multiplex PCR assay to detect M. bovis, M. californicum and M. bovigenitalium, and evaluate its analytical performance against traditional culture of bovine milk, semen and swab samples. The PCR specificity was determined and the limit of detection evaluated in spiked milk, semen and swabs. The PCR was then compared to culture on 474 field samples from individual milk, bulk tank milk (BTM), semen and swab (vaginal, preputial, nose and eye) samples. Specificity analysis produced appropriate amplification for all M. bovis, M. californicum and M. bovigenitalium isolates. Amplification was not seen for any of the other Mollicutes or eubacterial isolates. The limit of detection of the PCR was best in milk, followed by semen and swabs. When all three Mycoplasma species were present in a sample, the limit of detection increased. When comparing culture and PCR, overall there was no significant difference in the proportion of culture and PCR positive samples. Culture could detect significantly more positive swab samples. No significant differences were identified for semen, individual milk or BTM samples. PCR identified five samples with two species present. Culture followed by 16S-23S rRNA sequencing did not enable identification of more than one species. Therefore, the superior method for identification of M. bovis, M. californicum and M. bovigenitalium may be dependent on the sample type being analysed, and whether the identification of multiple target species is required.

Genetic characterization of Australian Mycoplasma bovis isolates through whole genome sequencing analysis

Mycoplasma bovis is a major pathogen in cattle causing mastitis, arthritis and pneumonia. First isolated in Australian cattle in 1970, M. bovis has persisted causing serious disease in infected herds. To date, genetic analysis of Australian M. bovis isolates has not been performed. With whole genome sequencing (WGS) becoming a common tool for genetic characterization, this method was utilized to determine the degree of genetic diversity among Australian M. bovis isolates collected over a nine year period (2006-2015) from various geographical locations, anatomical sites, and from clinically affected and non-clinical carrier animals. Eighty-two M. bovis isolates underwent WGS from which single nucleotide polymorphism (SNP) analysis, comparative genomics and analysis of virulence genes was completed. SNP analysis identified a single M. bovis strain circulating throughout Australia with marked genomic similarity. Comparative genomics suggested minimal variation in gene content between isolates from clinical and carrier animals, and between isolates recovered from different anatomical sites. A total of 50 virulence genes from the virulence factors database (VFDB) were identified as highly similar in the Australian isolates, while the presence of variable surface lipoprotein (vsp) genes was greatly reduced compared to reference strain M. bovis PG45. These results highlight that, while the introduction of multiple M. bovis strains has been prevented, elimination of the current strain has not been successful. The persistence of this strain may be due to the significant role that carrier animals play in harboring the pathogen. The similarity of clinical and non-clinical isolates suggests host and environmental factors play a significant role in determining host pathogen outcomes.

Mycoplasma mastitis in cattle: To cull or not to cull

Bovine mastitis caused by mycoplasmas, in particular Mycoplasma bovis, is a major problem for milk production and animal welfare in large dairy herds in the USA and a serious, although sporadic, disease in Europe and the Middle East. It causes severe damage to the udder of cattle and is largely untreatable by chemotherapy. Mycoplasma mastitis has a distinct epidemiology and a unique set of risk factors, the most important of which is large herd size. The disease is often self-limiting, disappearing within months of outbreaks, sometimes without deliberate intervention. Improved molecular diagnostic tests are leading to more rapid detection of mycoplasmas. Typing tests, such as multi-locus sequence typing, can help trace the source of outbreaks. An approach to successful control is proposed, which involves regular monitoring and rapid segregation or culling of infected cows. Serious consideration should be given by owners of healthy dairy herds to the purchase of M. bovis-free replacements. Increased cases of disease could occur in Europe and Israel if the trend for larger dairy herds continues.

An improved loop-mediated isothermal amplification assay for the detection of Mycoplasma bovis

We improved a loop-mediated isothermal amplification (LAMP) assay permitting sensitive and rapid Mycoplasma bovis detection. A total of 55 bacterial strains were examined in this study, including 33 M. bovis strains, 14 non-M. bovis mycoplasmas and eight non-mycoplasma bacterial strains. M. bovis was successfully detected by the LAMP assay within 60 min without cross-reaction to any other bacteria. Furthermore, a total of 135 nasal swab samples were tested directly using our LAMP assays, the previously reported LAMP assay, conventional PCR assay without pre-culture and comparing standard culture methods. The improved LAMP assay showed sensitivity and specificity of 97.2% and 90.9%, respectively (with a kappa coefficient of 0.8231), and the sensitivity of our revised LAMP assay was increased compared to existing methods.

Development and Evaluation of a Novel Taqman Real-Time PCR Assay for Rapid Detection of Mycoplasma bovis: Comparison of Assay Performance with a Conventional PCR Assay and Another Taqman Real-Time PCR Assay

The objective of this study was to develop and validate a Taqman real-time PCR assay for the detection of Mycoplasma bovis (M. bovis). Unique primers targeting the highly conserved house-keeping gene (uvrC) were designed and the probe sequence was derived from a previously published microarray study. There was 100% agreement in the outcome between our assay and the other two published assays for M. bovis detection. The analytical limit of detection of our assay is 83 copies of the uvrC gene. This assay was validated on a total of 214 bovine clinical specimens that were submitted to the Texas A&M Veterinary Medical Diagnostic Laboratory (TVMDL), Texas, USA. The specificity of the assay was assessed to be 100% since no cross-reactivity occurred with 22 other bacterial and other Mycoplasma species. We conclude that the uvrC gene serves as a good and reliable diagnostic marker for the accurate and rapid detection of M. bovis from a wider variety of specimen matrices.

Multilocus sequence typing of Mycoplasma bovis reveals host-specific genotypes in cattle versus bison

Mycoplasma bovis is a primary agent of mastitis, pneumonia and arthritis in cattle and the bacterium most frequently isolated from the polymicrobial syndrome known as bovine respiratory disease complex. Recently, M. bovis has emerged as a significant health problem in bison, causing necrotic pharyngitis, pneumonia, dystocia and abortion. Whether isolates from cattle and bison comprise genetically distinct populations is unknown. This study describes the development of a highly discriminatory multilocus sequencing typing (MLST) method for M. bovis and its use to investigate the population structure of the bacterium. Genome sequences from six M. bovis isolates were used for selection of gene targets. Seven of 44 housekeeping genes initially evaluated were selected as targets on the basis of sequence variability and distribution within the genome. For each gene target sequence, four to seven alleles could be distinguished that collectively define 32 sequence types (STs) from a collection of 94 cattle isolates and 42 bison isolates. A phylogeny based on concatenated target gene sequences of each isolate revealed that bison isolates are genetically distinct from strains that infect cattle, suggesting recent disease outbreaks in bison may be due to the emergence of unique genetic variants. No correlation was found between ST and disease presentation or geographic origin. MLST data reported here were used to populate a newly created and publicly available, curated database to which researchers can contribute. The MLST scheme and database provide novel tools for exploring the population structure of M. bovis and tracking the evolution and spread of strains.

A real-time PCR for detection and quantification of Mycoplasma ovipneumoniae

A real-time PCR for detection and quantification of M. ovipneumoniae was developed using 9 recently sequenced M. ovipneumoniae genomes and primers targeting a putative adhesin gene p113. The assay proved to be specific and sensitive (with a detection limit of 22 genomic DNA) and could quantify M. ovipneumoniae DNA over a wide linear range, from 2.2 × 10² to 2.2 × 10⁷ genomes.

Mortality of live export cattle on long-haul voyages: pathologic changes and pathogens

The cause of death in 215 cattle on 20 long-haul live export voyages from Australia to the Middle East, Russia, and China was investigated between 2010 and 2012 using gross, histologic, and/or molecular pathology techniques. A quantitative reverse transcription polymerase chain reaction (qRT-PCR) assay was used to detect nucleic acids from viruses and bacteria known to be associated with respiratory disease in cattle: Bovine coronavirus ( Betacoronavirus 1), Bovine herpesvirus 1, Bovine viral diarrhea virus 1 and 2, Bovine respiratory syncytial virus, Bovine parainfluenza virus 3, Histophilus somni, Mycoplasma bovis, Mannheimia haemolytica, and Pasteurella multocida. The most commonly diagnosed cause of death was respiratory disease (107/180, 59.4%), followed by lameness ( n = 22, 12.2%), ketosis ( n = 12, 6.7%), septicemia ( n = 11, 6.1%), and enteric disease ( n = 10, 5.6%). Two thirds (130/195) of animals from which lung samples were collected had histologic changes and/or positive qRT-PCR results indicative of infectious lung disease: 93 out of 130 (72%) had evidence of bacterial infection, 4 (3%) had viral infection, and 29 (22%) had mixed bacterial and viral infections, and for 4 (3%) the causative organism could not be identified. Bovine coronavirus was detected in up to 13% of cattle tested, and this finding is likely to have important implications for the management and treatment of respiratory disease in live export cattle. Results from the current study indicate that although overall mortality during live export voyages is low, further research into risk factors for developing respiratory disease is required.

Systemic mycoplasmosis with dystocia and abortion in a North American bison (Bison bison) herd

The current study describes a fatal Mycoplasma bovis infection in a North American bison ( Bison bison) cow and her aborted fetus in a herd suffering unusual mortality associated with dystocia and abortion. Postmortem evaluation of the subject case found severe caseonecrotic bronchopneumonia, chronic fibrinous pleuritis and pulmonary sequestra, foci of caseous necrosis in the kidneys, and necrotizing endometritis and placentitis. Histologic findings in the maternal tissues include endometrial and placental necrotizing vasculitis and changes in the lung similar to those previously described for M. bovis–associated pneumonia in feedlot bison. Gross and microscopic lesions were not observed in the fetus. Maternal lung, uterus, kidney, and placenta as well as fetal lung and kidney were positive for M. bovis by polymerase chain reaction (PCR) as were the Mycoplasma-like colonies cultured from these tissues. The presence of M. bovis in maternal and fetal tissues was further demonstrated using nucleic acid extracts in a pan- Mycoplasma SYBR Green PCR assay targeting the 16S-23S ribosomal RNA spacer region with post-PCR dissociation curve analysis and sequencing of the resulting amplicons. Immunohistochemistry (IHC) testing on maternal lung and uterine caruncle was strongly positive for M. bovis antigen. A variety of methods, including culture, PCR, and IHC, failed to identify other bacterial or viral pathogens in any of the tissues evaluated. These data are the first to implicate M. bovis as a cause of placentitis and abortion in bison.

Necrotic pharyngitis associated with Mycoplasma bovis infections in American bison (Bison bison)

Mycoplasma bovis has emerged as a significant and costly infectious disease problem in bison, generally presenting as severe, caseonecrotic pneumonia. Three diagnostic cases in which M. bovis is associated with necrotic pharyngitis in bison are described in the current study. The bacterium was isolated from lesions of the pharynx or lung of 3 American bison ( Bison bison), at 2 different locations in the upper Midwestern United States, with severe, necrotic pharyngeal abscesses. Chronic caseonecrotic inflammation typical of M. bovis infection in bovines was observed microscopically in the pharynxes of affected bison. A mixed population of bacteria was recovered from the pharyngeal lesions, and Trueperella pyogenes, a frequent secondary pathogen in ruminant respiratory disease, was consistently isolated from the affected animals. Distinctive histopathological features of the pharyngeal lesions favor causation by M. bovis, although a role for T. pyogenes in the clinical presentation cannot be excluded. Veterinarians and producers working with bison should be aware that M. bovis may be associated with pharyngitis in bison.

Technical Advances in Veterinary Diagnostic Microbiology

Forming a significant part of biomass on earth, microorganisms are renowned for their abundance and diversity. From submicroscopic infectious particles (viruses), small unicellular cells (bacteria and yeasts) to multinucleate and multicellular organisms (filamentous fungi, protozoa, and helminths), microorganisms have found their way into virtually every environmental niche, and show little restrain in making their presence felt. While a majority of microorganisms are free-living and involved in the degradation of plant debris and other organic materials, others lead a symbiotic, mutually beneficial life within their hosts. In addition, some microorganisms have the capacity to take advantage of temporary weaknesses in animal and human hosts, causing notable morbidity and mortality. Because clinical manifestations in animals and humans resulting from infections with various microorganisms are often nonspecific (e.g., general malaise and fever), it is necessary to apply laboratory diagnostic means to identify the culprit organisms for treatment and prevention purposes.