Serological diagnosis of enzootic pneumonia of swine by a double-sandwich enzyme-linked immunosorbent assay using a monoclonal antibody and recombinant antigen (P46) of Mycoplasma hyopneumoniae

Improving Mycoplasma hyopneumoniae diagnostic capabilities by harnessing the infection dynamics

Mycoplasma hyopneumoniae remains one of the most problematic bacterial pathogens for pig production. Despite an abundance of observational and laboratory testing capabilities for this organism, diagnostic interpretation of test results can be challenging and ambiguous. This is partly explained by the chronic nature of M. hyopneumoniae infection and its tropism for lower respiratory tract epithelium, which affects diagnostic sensitivities associated with sampling location and stage of infection. A thorough knowledge of the available tools for routine M. hyopneumoniae diagnostic testing, together with a detailed understanding of infection dynamics, are essential for optimizing sampling strategies and providing confidence in the diagnostic process. This study reviewed known information on sampling and diagnostic tools for M. hyopneumoniae and summarized literature reports of the dynamics of key infection outcomes, including clinical signs, lung lesions, pathogen detection, and humoral immune responses. Such knowledge could facilitate better understanding of the performance of different diagnostic approaches at various stages of infection.

Influence of parity and reproductive stage on the prevalence of Mycoplasma hyopneumoniae in breeding animals in belgian farrow-to-finish pig herds

Background

Dam-to-piglet transmission plays an important role in the epidemiology of enzootic pneumonia on farms. Although Mycoplasma hyopneumoniae (M. hyopneumoniae) infections in breeding animals are often subclinical, their control could have a positive effect on M. hyopneumoniae infection levels in fattening pigs. This study investigated the presence of M. hyopneumoniae in the breeding population of ten Belgian farrow-to-finish farms suspected by the herd veterinarian to be M. hyopneumoniae infected. Gilt vaccination against M. hyopneumoniae prior to first insemination was practiced on nine of the ten farms. At four different time points in the reproductive cycle 20 animals were sampled on each farm, namely 30–40 days of gestation, 75–85 days of gestation, 3–5 days after farrowing, and 1–3 days after weaning. In total, tracheobronchial swabs and blood samples were collected from 344 gilts and 456 sows (n = 80/farm). Swabs were analysed for the presence of M. hyopneumoniae DNA using nested PCR and M. hyopneumoniae-specific antibodies were detected in serum with a commercial ELISA. Generalized linear mixed models with farm as random factor were used to test the effect of time point in the reproductive cycle and parity on M. hyopneumoniae PCR prevalence and seroprevalence.

Results

M. hyopneumoniae PCR prevalence ranged between 0% and 43.8% at the farm level and the seroprevalence between 32.5% and 93.8%. Gilts were significantly more M. hyopneumoniae PCR positive than sows at the 2-4th parity (P = 0.02) and > 4th parity (P = 0.02). At 30–40 days of gestation, significantly more breeding animals were PCR positive as compared to 75–85 days of gestation (P = 0.04), 3–5 days after farrowing (P = 0.02) and 1–3 days after weaning (P = 0.02). Gilts had significantly more often M. hyopneumoniae-specific antibodies than sows (P = 0.03).

Conclusions

M. hyopneumoniae PCR prevalence varied a lot between farms and due to gilt vaccination the number of animals with M. hyopneumoniae-specific antibodies was high on most farms. Gilts were more often M. hyopneumoniae PCR positive than sows and positive animals were mostly found at 30–40 days of gestation. This emphasizes the importance of a sufficiently long quarantine period and proper gilt acclimation practices before introducing gilts to the sow herd.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40813-022-00267-w.

Mycoplasma hyopneumoniae variability: Current trends and proposed terminology for genomic classification

Mycoplasma hyopneumoniae (M. hyopneumoniae) is the aetiologic agent of enzootic pneumonia in swine, a prevalent chronic respiratory disease worldwide. Mycoplasma hyopneumoniae is a small, self-replicating microorganism that possesses several characteristics allowing for limited biosynthetic abilities, resulting in the fastidious, host-specific growth and unique pathogenic properties of this microorganism. Variation across several isolates of M. hyopneumoniae has been described at antigenic, proteomic, transcriptomic, pathogenic and genomic levels. The microorganism possesses a minimal number of genes that regulate the transcription process. Post-translational modifications (PTM) occur frequently in a wide range of functional proteins. The PTM by which M. hyopneumoniae regulates its surface topography could play key roles in cell adhesion, evasion and/or modulation of the host immune system. The clinical outcome of M. hyopneumoniae infections is determined by different factors, such as housing conditions, management practices, co-infections and also by virulence differences among M. hyopneumoniae isolates. Factors contributing to adherence and colonization as well as the capacity to modulate inflammatory and immune responses might be crucial. Different components of the cell membrane (i.e. proteins, glycoproteins and lipoproteins) may serve as adhesins and/or be toxic for the respiratory tract cells. Mechanisms leading to virulence are complex and more research is needed to identify markers for virulence. The utilization of typing methods and complete or partial-gene sequencing for M. hyopneumoniae characterization has increased in diagnostic laboratories as control and elimination strategies for this microorganism are attempted worldwide. A commonly employed molecular typing method for M. hyopneumoniae is Multiple-Locus Variable number tandem repeat Analysis (MLVA). The agreement of a shared terminology and classification for the various techniques, specifically MLVA, has not been described, which makes inferences across the literature unsuitable. Therefore, molecular trends for M. hyopneumoniae have been outlined and a common terminology and classification based on Variable Number Tandem Repeats (VNTR) types has been proposed.

Rapid and sensitive detection of Mycoplasma hyopneumoniae by recombinase polymerase amplification assay

Mycoplasma hyopneumoniae is the etiological agent of swine enzootic pneumonia, which is associated with high economic losses in swine production worldwide. In this study, recombinase polymerase amplification assays using real-time fluorescence detection (real-time RPA) and lateral flow strip detection (LFS RPA) were developed to detect M. hyopneumoniae based on the conserved region of the mhp165 gene. Real-time RPA was performed in Genie III at 39 °C for 20 min, while the LFS RPA was performed in an incubator block at 39 °C for 15 min, and the products were visible on the LFS inspected by the naked eyes within 2 min. Both assays were specific for M. hyopneumoniae, as there were no cross-reactions with other pathogens tested. The limit of detection of both RPA assay was 5.0 × 10² fg of M. hyopneumoniae DNA, which was the same as that of a real-time PCR assay. Of the 146 clinical samples, M. hyopneumoniae DNA was identified in 41, 42, and 47 samples by the real-time RPA, LFS RPA and real-time PCR, respectively. Compared to real-time PCR, the real-time RPA and LFS RPA assays showed diagnostic specificity of 100%, a diagnostic sensitivity of 87.23% and 89.36%, and a kappa value of 0.903 and 0.909, respectively. These results have demonstrated that the developed RPA assays are suitable for rapid and reliable detection of M. hyopneumoniae in diagnostic laboratory and at point-of-need facility.

First report of Mycoplasma hyopneumoniae seroprevalence in farmed wild boars in China

Porcine enzootic pneumonia caused by Mycoplasma hyopneumoniae affects the global pig industry with significant economic losses. It is yet to know whether wild boars in China were infected with M. hyopneumoniae. The present study was conducted to examine the seroprevalence and to evaluate risk factors of M. hyopneumoniae infection in farmed wild boars in China. A total of 882 serum samples were collected from farmed wild boars in Jilin City, Siping City and Baishan City in Jilin Province, northeastern China from April 2015 to February 2016, and were examined by the double sandwich enzyme-linked immunosorbent assay (ELISA). Seventy-eight out of 882 (8.8%) serum samples were M. hyopneumoniae-seropositive. Among region groups, wild boars from Jilin city (11.7%, 33/281) had the highest seropositivity, followed by Siping city (11%, 29/263) and Baishan city (4.7%, 16/338), and the difference was statistically significant (P = 0.0031). The M. hyopneumoniae seroprevalence in the female wild boars (9.0%, 75/831) was higher than that in the male wild boars (5.9%, 3/51) (P = 0.4429). The results of this investigation showed that farmed wild boars were susceptible to M. hyopneumoniae. Logistic regression analysis showed that there is a significant correlation between the geographical area and M. hyopneumoniae infection, which may be related to the regional environment. This is the first report of M. hyopneumoniae seroprevalence in farmed wild boars in China, which provided baseline information for further studies and control of M. hyopneumoniae infection in wild boars in China.

Development of a blocking ELISA for detection of Mycoplasma hyopneumoniae infection based on a monoclonal antibody against protein P65

Mycoplasma hyopneumoniae causes porcine enzootic pneumonia, an economically important disease of swine. A more sensitive and reliable method for detection of serum antibodies is needed for epidemiological investigations and to evaluate the effect of immunization. We expressed the M. hyopneumoniae protein P65 in Escherichia coli and produced a monoclonal antibody (mAb) that bound specifically to recombinant P65. Using this mAb, a blocking enzyme linked immunosorbent assay (ELISA) was developed. The blocking ELISA had similar specificity to and sensitivity with the commercial ELISA produced by IDEXX. Thus, this blocking ELISA is a useful test for serological confirmation of M. hyopneumoniae infection.

Biology and Diseases of Swine

Swine are used in biomedical research as models for biomedical research and for teaching. This chapter covers normative biology and behavior along with common and emerging swine diseases. Xenotransplantation is discussed along with similarities and differences of swine immunology.

Antibody responses of swine following infection with Mycoplasma hyopneumoniae, M. hyorhinis, M. hyosynoviae and M. flocculare

Several mycoplasma species possessing a range of virulence have been described in swine. The most commonly described are Mycoplasma hyopneumoniae, Mycoplasma hyorhinis, Mycoplasma hyosynoviae, and Mycoplasma flocculare. They are ubiquitious in many pig producing areas of the world, and except for M. hyopneumoniae, commercial antibody-based assays are lacking for most of these. Antibody cross-reactivity among these four mycoplasma species is not well characterized. Recently, the use of pen-based oral fluids for herd surveillance is of increasing interest. Thus, this study sought to measure pig antibody responses and the level of cross-reactivity in serum and pen-based oral fluids after challenge with four species of swine mycoplasmas. Four groups of four mycoplasma-free growing pigs were separately inoculated with the different mycoplasma species. Pen-based oral fluids and serum samples were collected weekly until necropsy. Species-specific Tween 20 ELISAs were used to measure antibody responses along with four other commercial M. hyopneumoniae ELISAs. Animals from all groups seroconverted to the challenge species of mycoplasma and no evidence of cross-contamination was observed. A delayed antibody response was seen with all but M. hyorhinis-infected pigs. Cross-reactive IgG responses were detected in M. hyopneumoniae- and M. flocculare-infected animals by the M. hyorhinis Tween 20 ELISA, while sera from M. hyosynoviae and M. flocculare-infected pigs were positive in one commercial assay. In pen-based oral fluids, specific anti-M. hyopneumoniae IgA responses were detected earlier after infection than serum IgG responses. In summary, while some antibody-based assays may have the potential for false positives, evidence of this was observed in the current study.

Loop-mediated isothermal amplification for rapid and convenient detection of Mycoplasma hyopneumoniae

Loop-mediated isothermal amplification (LAMP), a novel method of gene amplification, was employed in this study for detecting Mycoplasma hyopneumoniae in the respiratory tract or lungs of swine. The pathogen can be detected in LAMP reactions containing as few as 10 fg purified target DNA (10 copies of M. hyopneumoniae genome) within 30 min, which was comparable to real-time PCR. After 30-min reaction at 63 °C, the addition of a certain amount of dye (SYBR Green I and hydroxyl naphthol blue at a proper ratio) into the LAMP reaction system makes the results easily determined as positive or negative by visual inspection. In addition, the LAMP was able to distinguish between M. hyopneumoniae and other closely-related mycoplasma strains, indicating a high degree of specificity. The LAMP assay was more simple and cheap, since the reaction could be completed under isothermal conditions and less laboratorial infrastructure are required. And, it was proven reliable for M. hyopneumoniae diagnosis of nasal swab and lung samples from the field.

Bi-antigenic immunoassay models based on the recombinant PvpA proteins for Mycoplasma gallisepticum diagnosis in chickens

The present study aimed to produce the relatively conserved central fragment of the Mycoplasma gallisepticum PvpA cytadhesin as recombinant antigen and to determine its species-specific diagnostic potential in comparison with the full-length recombinant rPvpA336 protein. For this purpose, a recombinant protein (rPvpA134) consisting of 134 amino acids with apparent molecular mass of 27 kD was produced and highly purified. The rPvpA134 protein was composed of the amino acid residues at positions 133-265 with respect to the wild-type PvpA. Two bi-antigenic diagnostic models based on Western blot and enzymatic rapid immunofiltration assay (ERIFA) were developed to compare simultaneously the diagnostic potential of the recombinant antigens rPvpA134 and rPvpA336. Although 40% of the confirmed rPvpA336-positive chicken sera were detected as reactive with rPvpA134, this protein would be a useful secondary diagnostic antigen with which to confirm species-specific antibody response for monitoring M. gallisepticum infections. It can be concluded from the present study that 2 bi-antigenic models were successfully adapted to the specific diagnosis of chicken M. gallisepticum. Furthermore, by virtue of its simplicity and rapidity, the ERIFA model has multi-antigenic application potential, making it an alternative field test that is widely applicable in the veterinary diagnostic field.

Validation of nested PCR and a selective biochemical method as alternatives for mycoplasma detection

Direct culture is the most common way to reliably detect mycoplasma, but it is not practical for the qualitative control of cell therapeutics because of the elaborate culture medium, the prolonged incubation time, and the large sample volumes. Here, we chose two alternative methods using commercial detection kits, the PCR mycoplasma detection kit with nested PCR and the selective biochemical method, MycoAlert(®), and validated them with the direct culture method as a reference. We tested eight mycoplasma species and five validation parameters: specificity, detection limit, robustness, repeatability, and ruggedness, based on the regulatory guidelines in the US Pharmacopoeia. All experiments were performed using fibroblasts spiked with mycoplasma. Specificity tests for both methods included all mycoplasma species, except Mycoplasma pneumonia and M. genitalium for the nested PCR and Ureaplasma urealyticum for the MycoAlert(®) assay. Regarding the detection limit, the nested PCR proved to be as sensitive as the direct culture method and more sensitive than the MycoAlert(®) assay. The predicted median for probit = 0.9 was 54 (44-76) CFU/ml for M. hyorhinis and 16 (13-23) CFU/ml for M. hominis by the nested PCR, but 431 (346-593) CFU/ml and 105 (87-142) CFU/ml, respectively, with MycoAlert(®). Changes in the concentration of reagents, reagent lot, or individual analysts did not influence the results of the examined methods. The results of this study support nested PCR as a valuable alternative for mycoplasma detection.

Development of a quantitative Real-Time TaqMan PCR assay for determination of the minimal dose of Mycoplasma hyopneumoniae strain 116 required to induce pneumonia in SPF pigs

AIMS

A triplex real-time PCR assay to quantify Mycoplasma hyopneumoniae in specimens from live and dead pigs was developed and validated. The minimal dose of Myc. hyopneumoniae required to induce pneumonia in specific pathogen-free pigs was determined.

METHODS AND RESULTS

This TaqMan test simultaneously detected three genes encoding the proteins P46, P97 and P102. All Myc. hyopneumoniae strains analysed were detected, including strains isolated in three countries (France, England and Switzerland) and from several pig farms (n = 33), and the test was specific. The estimated detection thresholds were 1.3 genome equivalents (microl(-1)) for the targets defined in p97 and p102 genes and 13 genome equivalents (microl(-1)) for the segment defined in the p46 gene. This test was used to quantify Myc. hyopneumoniae in specimens sampled from experimentally infected pigs. In live pigs, c. 10(7), 10(8) and 10(10) genome equivalents (ml(-1)) of Myc. hyopneumoniae were detected in the nasal cavities, tonsils and trachea samples, respectively. In dead pigs, 10(8)-10(10) genome equivalents (ml(-1)) of Myc. hyopneumoniae were detected in the lung tissue with pneumonia. The estimated minimal dose of Myc. hyopneumoniae required to induce pneumonia was 10(5) colour-changing units (CCU) per pig (corresponding to 10(8) mycoplasmas).

CONCLUSION

The triplex RT-PCR test was validated and can be used for testing samples taken on the pig farms.

SIGNIFICANCE AND IMPACT OF THE STUDY

This test should be a very useful tool in pig herds to control enzootic pneumonia or healthy carrier pigs and to study the dynamics of Myc. hyopneumoniae infections.

Seroprevalence and risk factors associated with seropositivity in sows from 67 herds in north-west Germany infected with Mycoplasma hyopneumoniae

Risk factors for the spread of Mycoplasma hyopneumoniae in sows have not been studied although vertical transmission from sows to their offspring is considered a significant risk factor in the development of enzootic pneumonia in growers and finishers. Seropositivity for M. hyopneumoniae in sows, as assessed by commercial ELISA, is a possible indicator of infection pressure among sows. The objective of this study was to estimate seroprevalence and associated risk factors of a sow being seropositive for M. hyopneumoniae. A cross-sectional study was carried out in 2578 sows from 67 herds in north-west Germany. Data concerning general herd characteristics, acclimatisation practices, indoor and outside contacts, as well as data describing the immediate local environment were collected during a herd visit via questionnaire. Blood samples were seropositive in 65% of the 2578 sows, and all herds had >/=14% seropositive sows. Data analysis was performed in two steps. First, univariate analysis of predictor variables for the risk of a sow being seropositive for M. hyopneumoniae was performed using chi-square test. Secondly, all variables associated with the risk of a sow being seropositive (P</=0.25) were included in a multivariate model using a generalised linear model. The risk of a sow being seropositive for M. hyopneumoniae was increased in herds with two- or three-site production (OR 1.50), when piglets were not vaccinated against M. hyopneumoniae (OR 1.81), in herds with a 2-week farrowing intervals (OR 1.84) and in herds without all-in/all-out management of the farrowing units (OR 1.37). The lack of an acclimatisation period for replacement boars was also associated with the risk of a sow being seropositive (OR 2.10). The results indicate that M. hyopneumoniae seropositivity is common in sows in north-west Germany and is influenced by various management factors. It is recommended that evaluation of sow herd management should be included in any strategic health plan to control M. hyopneumoniae infection.

Proteomic survey of the pathogenic Mycoplasma hyopneumoniae strain 7448 and identification of novel post-translationally modified and antigenic proteins

Mycoplasma hyopneumoniae is an important pathogen for pigs, being the causative agent of enzootic pneumonia. Recently, the genome sequences of three strains, J, 7448 and 232 have been reported. Here, we describe the results of a proteomic analysis, based on two-dimensional gel electrophoresis of soluble protein extracts, immunoblot and mass spectrometry, which was carried out aiming the identification of gene products and antigenic proteins from the M. hyopneumoniae pathogenic strain 7448. A preliminary M. hyopneumoniae proteome map in two pH ranges (3-10 and 4-7) was produced. A total of 31 different coding DNA sequences (CDSs), including three hypothetical ones, were experimentally verified with the identification of the corresponding protein products by matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry. According to the Clusters of Orthologous Groups (COG) functional classification, the identified proteins were assigned to the groups of metabolism (13), cellular processes (5) and information and storage processing (4). Nine of the identified proteins were not classifiable by COG, including some related to cytoadherence and possibly involved in pathogenicity. Moreover, at least five highly antigenic proteins of M. hyopneumoniae were identified by immunoblots, including four novel ones (a heat shock protein 70, an elongation factor Tu, a pyruvate dehydrogenase E1-beta subunit and the P76 membrane protein). The now available proteome map is expected to serve as a reference for comparative analyses between M. hyopneumoniae pathogenic and non-pathogenic strains, and for methabolic studies based on cells cultured under modified conditions.

Evaluation of an Indirect Enzyme-Linked Immunosorbent Assay (ELISA) using Recombinant Toxin for Detection of Antibodies against Pasteurella multocida Toxin

To facilitate the control of progressive atrophic rhinitis (PAR) of swine caused by toxigenic Pasteurella multocida, an enzyme-linked immunosorbent assay (ELISA) and a serum neutralization test (NT) have recently been developed to detect antibodies against the P. multocida dermonecrotic toxin (PmDNT). However, the NT is a cumbersome and time-consuming technique. To overcome these drawbacks, we developed an indirect ELISA, using recombinant PmDNT expressed in Escherichia coli, for the detection of antibodies to PmDNT in serum samples from pigs. The practical usefulness of this ELISA was compared with the NT using serum samples obtained from experimentally infected and naturally infected pigs. In the pigs experimentally inoculated with vaccine including PmDNT toxoid, the ELISA and neutralization antibodies were detected at almost the same time, and a good correlation was demonstrated between both tests (P<0.01, R(2)=0.807). Therefore, the ELISA can be used to evaluate the immune reaction of pigs after vaccination with P. multocida toxoid. In a survey conducted on a field herd with a history of clinical AR, the seropositivity by ELISA in pigs of age 4.5-6 months was increased even though the NT was negative, and the correlation was low between the results obtained with the two tests (P<0.01, R(2)=0.38). Therefore, the results indicated that this ELISA might be a useful alternative to the NT currently used to detect the antibody to PmDNT after vaccination or infection with P. multocida.