Cross reactivity among the swine mycoplasmas as identified by protein microarray

Development of ELISA Using Recombinant Proteins for the Diagnosis of Mycoplasma hyopneumoniae Infection

In order to develop a more sensitive and reliable method for detection of serum antibodies against Mycoplasma hyopneumoniae infection in pigs, six recombinant proteins of M. hyopneumoniae (P102, P95, P46, P97 like, Lppt, and hypothetical P987) were used for the standardization of an indirect enzyme-linked immunosorbent assay (ELISA). The proteins were evaluated against 50 sera of the specific pathogen-free and 50 sera of pigs with lesions suggestive of infection. The sensitivity was 88%, 86%, 78%, 74%, 66%, and 60% for the proteins P102, P95, P46, P97 like, Lppt, and hypothetical protein P987, respectively. Moreover, the proteins were used to establish the seroprevalence in two different commercial herds (254 sera pigs from farm considered free of M. hyopneumoniae and 246 from farm with clinical signs of enzootic pneumonia and positive serology for M. hyopneumoniae) and the positive rate was 65.2% for P95, 54.6% for P102, 40.2% for P46, 37.2% for P97 like, 17.4% for the hypothetical P987, and 14% for Lppt protein. In addition, the ELISA with six recombinant proteins was compared to commercial HerdCheck kit using 118 random pig sera samples and the results showed that ELISA with recombinant proteins were more sensitive than the commercial test. These data show that the recombinant proteins P95 and P102 are potential targets to be used in diagnostic tests to detect antibodies against M. hyopneumoniae. Although more studies are necessary, this study provides insights that these recombinant proteins can be useful in epidemiological investigations and as potential biomarkers in differentiating infected animals from those vaccinated.

Construction of Mycoplasma hyopneumoniae P97 Null Mutants

Mycoplasma hyopneumoniae is the causative agent of enzootic pneumonia, a world-wide problem in the pig industry. This disease is characterized by a dry, non-productive cough, labored breathing, and pneumonia. Despite years of research, vaccines are marginally effective, and none fully protect pigs in a production environment. A better understanding of the host-pathogen interactions of the M. hyopneumoniae-pig disease, which are complex and involve both host and pathogen components, is required. Among the surface proteins involved in virulence are members of two gene families called P97 and P102. These proteins are the adhesins directing attachment of the organism to the swine respiratory epithelium. P97 is the major ciliary binding adhesin and has been studied extensively. Monoclonal antibodies that block its binding to swine cilia have contributed extensively to its characterization. In this study we use recombination to construct null mutants of P97 in M. hyopneumoniae and characterize the resulting mutants in terms of loss of protein by immunoblot using monoclonal antibodies, ability to bind purified swine cilia, and adherence to PK15 cells. Various approaches to recombination with this fastidious mycoplasma were tested including intact plasmid DNA, single-stranded DNA, and linear DNA with and without a heterologous RecA protein. Our results indicate that recombination can be used to generate site-specific mutants in M. hyopneumoniae. P97 mutants are deficient in cilia binding and PK15 cell adherence, and lack the characteristic banding pattern seen in immunoblots developed with the anti-P97 monoclonal antibody.

Performance of Commercial Mycoplasma hyopneumoniae Serum Enzyme-Linked Immunosorbent Assays under Experimental and Field Conditions

Mycoplasma hyopneumoniae is an economically significant pathogen of swine. M. hyopneumoniae serum antibody detection via commercial enzyme-linked immunosorbent assays (ELISAs) is widely used for routine surveillance in commercial swine production systems. Samples from two studies were used to evaluate assay performance. In study 1, 6 commercial M. hyopneumoniae ELISAs were compared using serum samples from 8-week-old cesarean-derived, colostrum-deprived (CDCD) pigs allocated to the following 5 inoculation groups of 10 pigs each: (i) negative control, (ii) Mycoplasma flocculare (strain 27399), (iii) Mycoplasma hyorhinis (strain 38983), (iv) Mycoplasma hyosynoviae (strain 34428), and (v) M. hyopneumoniae (strain 232). Weekly serum and daily oral fluid samples were collected through 56 days postinoculation (dpi). The true status of pigs was established by PCR testing on oral fluids samples over the course of the observation period. Analysis of ELISA performance at various cutoffs found that the manufacturers' recommended cutoffs were diagnostically specific, i.e., produced no false positives, with the exceptions of 2 ELISAs. An analysis based on overall misclassification error rates found that 4 ELISAs performed similarly, although one assay produced more false positives. In study 2, the 3 best-performing ELISAs from study 1 were compared using serum samples generated under field conditions. Ten 8-week-old pigs were intratracheally inoculated with M. hyopneumoniae Matched serum and tracheal samples (to establish the true pig M. hyopneumoniae status) were collected at 7- to 14-day intervals through 98 dpi. Analyses of sensitivity and specificity showed similar performance among these 3 ELISAs. Overall, this study provides an assessment of the performance of current M. hyopneumoniae ELISAs and an understanding of their use in surveillance.

Efficacy in pigs of a new inactivated vaccine combining porcine circovirus type 2 and Mycoplasma hyorhinis

Coinfection with porcine circovirus type 2 (PCV2) and Mycoplasma hyorhinis (Mhr) can induce more-severe disease than a single infection with either. We evaluated the efficacy of a new vaccine combining inactivated PCV2 and Mhr, in a model of PCV2 and Mhr infection. Twenty-five 35-day-old PCV2- and Mhr-free pigs were randomly divided into five groups, with five pigs in each group. The pigs in groups 1 and 2 were vaccinated with the combined vaccine and then challenged with Mhr or PCV2, respectively. The pigs in groups 3 and 4 were not vaccinated and then challenged with PCV2 or Mhr, respectively, and group 5 was used as the unvaccinated unchallenged control. Two weeks after booster immunization via the intramuscular route, all the pigs except those in control group 5 were challenged with PCV2 or Mhr. All the pigs were euthanized 28 days after challenge. The pigs in vaccinated groups 1 and 2 showed a significant increase in weight after challenge with PCV2 or Mhr (P < 0.001), with an average daily gain (ADG) of 0.315 kg compared with unvaccinated groups 3 and 4 (0.279 kg). Mhr was isolated from the unvaccinated pig lungs after Mhr challenge, whereas it was not isolated from the vaccinated pigs. No PCV2 or Mhr was detected with PCR or histochemical staining in vaccinated groups 1 and 2. A statistical analysis showed that the PCV2 and Mhr combined vaccine providing protected against PCV2 infection causing viremia and inguinal lymphadenopathy (5 pigs protected out 5) or against Mhr infection causing fiber inflammation (4 pigs out 5). Thus, we have developed an effective combined vaccine for the prevention and control of PCV2 or Mhr infections in swine herds, this will help reduce prevalence of PCV2 and Mhr coinfections.

Comparison of the sensitivity of laryngeal swabs and deep tracheal catheters for detection of Mycoplasma hyopneumoniae in experimentally and naturally infected pigs early and late after infection

Detection of Mycoplasma hyopneumoniae infection in live pigs is a critical component to measure the success of disease control or elimination strategies. However, in vivo diagnosis of M. hyopneumoniae is difficult and the imperfect sensitivity of diagnostic tools has been deemed as one of the main challenges. Here, the sensitivity of laryngeal swabs and deep tracheal catheters for detection of M. hyopneumoniae early and late after infection was determined using inoculation status as a gold standard in experimentally infected pigs and a Bayesian approach in naturally infected pigs. Three-hundred and twenty 8-week old seeder pigs were intra-tracheally inoculated with M. hyopneumoniae strain 232 and immediately placed with 1920 contact pigs to achieve a 1:6 seeder-to-contact ratio. A subset of seeders and contacts were longitudinally sampled at 7, 28, 97, and 113 days post-inoculation (dpi) and at 28, 56, 84, and 113 days post-exposure (dpe), respectively, using laryngeal swabs and deep tracheal catheters. Samples were tested for M. hyopneumoniae by a species-specific real-time PCR. The sensitivity of deep tracheal catheters was higher than the one obtained in laryngeal swabs at all samplings (seeders: 36% higher than laryngeal swabs at 7 dpi, 29% higher at 97 dpi, and 44% higher at 113 dpi; contacts: 51% higher at 56 dpe, 42% higher at 84 dpe, and 32% higher at 113 dpe). Our study indicates that deep tracheal catheters were a more sensitive sample than laryngeal swabs. The sensitivity of both sample types varied over time and by exposure method, and these factors should be considered when designing diagnostic strategies.

Identification of specific B cell linear epitopes of mycoplasma hyorhinis P37 protein using monoclonal antibodies against baculovirus-expressed P37 protein

BACKGROUND

Mycoplasma hyorhinis (Mhr) is the etiologic agent of lameness and polyserositis in swine. P37 is a membrane protein of Mhr that may be an important immunogen and is a potential target for diagnostic development. However, there is little information concerning Mhr P37 protein epitopes. A precise analysis of the P37 protein epitopes should extend our understanding of the antigenic composition of the P37 protein and the humoral immune responses to Mhr infection. Investigating the epitopes of Mhr P37 will help to establish a detection method for Mhr in tissue and provide an effective tool for detecting Mhr infection.

RESULTS

Western blot and indirect immunofluorescence assays (IFA) confirmed that the expressed P37 protein was recognized by Mhr-positive porcine and mouse sera. Furthermore, the P37 protein was purified using affinity chromatography and used to immunize mice for hybridoma cell fusion. Four monoclonal antibodies (mAbs) found to be positive for Mhr were detected in infected lung tissue. A panel of truncated P37 proteins was used to identify the minimal B cell linear epitopes of the protein based on these mAbs. The core epitope was determined to be ²⁰⁶KIKKAWNDKDWNTFRNF²²²_. CONCLUSIONS: In this study, we identified 17 critical amino acids that determine the epitope of the P37 protein of Mhr. This study identified mAbs that could provide useful tools for investigating the Mhr P37 antigenic core epitope (amino acids 206-222) and detecting Mhr-specific antigens in infected tissue.

Utilization of macrophage extracellular trap nucleotides by Mycoplasma hyopneumoniae

Mycoplasma hyopneumoniae is the causative agent of enzootic pneumonia in swine, an important disease worldwide. It has finite biosynthetic capabilities, including a deficit in de novo nucleotide synthesis. The source(s) for nucleotides in vivo are unknown, but mycoplasmas are known to carry membrane-bound nucleases thought to participate in the acquisition of nucleotides from host genomic DNA. Recent research has demonstrated that neutrophils can produce extracellular traps (NETs), chromatin NETs decorated with granular proteins to interact with and eliminate pathogens. We hypothesized that M. hyopneumoniae could utilize its membrane nuclease to obtain nucleotides from extracellular traps to construct its own DNA. Using the human monocytic cell line THP-1, we induced macrophage extracellular traps (METs), which are structurally similar to NETs. The thymidine analogue ethynyl deoxyuridine (EdU) was incorporated into THP-1 DNA and METs were induced. When incubated with M. hyopneumoniae, METs were degraded and the modified nucleotide label could be co-localized within M. hyopneumoniae DNA. When the nucleases were inhibited, MET degradation and nucleotide transfer were also inhibited. Controls confirmed that the EdU originated directly from the METs and not from free nucleotides arising from intracellular pools released during extrusion of the chromosomal DNA. M. hyopneumoniae incorporated labelled nucleotides more efficiently when 'fed' on METs than from free nucleotides in the medium, suggesting a tight linkage between nuclease degradation of DNA and nucleotide transport. These results strongly suggest that M. hyopneumoniae could degrade extracellular traps formed in vivo during infection and incorporate those host nucleotides into its own DNA.

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.

Analysis of swine antigen-specific antibody responses to Mycoplasma hyopneumoniae infection determined by protein microarray

Pigs harbor several different species of mycoplasmas, of which Mycoplasma hyopneumoniae presents the most significant economic impact on the swine industry. While ELISAs are the predominant diagnostic assay to measure antibody responses during infection with M. hyopneumoniae, the assay itself is only a rough estimate of the total antibody response. It lends little information on pathogen-wide antigen-specific responses. In addition, antibody responses to M. hyopneumoniae as measured by ELISA are slow to develop in infected swine. Our goal was to determine if a protein microarray could be more sensitive and informative of the serological responses of pigs to M. hyopneumoniae infection. The gene sequences of approximately 50 M. hyopneumoniae surface proteins or protein fragments were cloned, mutated to remove UGA codons, expressed in Escherichia coli and purified. The arrays were used to interrogate pig sera from various sources. Sera from naturally-infected swine gave some variability in antigen-specific responses, but, unexpectedly, the responses against the C-terminal portion of the major adhesin P97 was weak in all animals, including those that were experimentally infected. In two of four 118-day experimentally-infected caesarian-derived colostrum-deprived pigs, the strongest antibody responses occurred on days 30 and 54 against members of the P97/P102 paralog families. Our Day 0 results in the other two animals indicate that although thought to be mycoplasma free by all known criteria (serology and PCR), they may have harbored an inapparent Mycoplasma infection. In summary, the protein microarray has the potential to identify new targets for assay development to enhance sensitivity of antibody-based assays.

Differential secretome profiling of a swine tracheal cell line infected with mycoplasmas of the swine respiratory tract

Mycoplasma hyopneumoniae and Mycoplasma flocculare are genetically similar. However, M. hyopneumoniae causes porcine enzootic pneumonia, while M. flocculare is a commensal bacterium. M. hyopneumoniae and M. flocculare do not penetrate their host cells, and secreted proteins are important for bacterium-host interplay. Thus, the secretomes of a swine trachea cell line (NPTr) infected with M. hyopneumoniae 7448 (a pathogenic strain), M. hyopneumoniae J (a non-pathogenic strain) and M. flocculare were compared to shed light in bacterium-host interactions. Medium from the cultures was collected, and secreted proteins were identified by a LC-MS/MS. Overall numbers of identified host and bacterial proteins were, respectively, 488 and 58, for NPTr/M. hyopneumoniae 7448; 371 and 67, for NPTr/M. hyopneumoniae J; and 203 and 81, for NPTr/M. flocculare. The swine cells revealed different secretion profiles in response to the infection with each M. hyopneumoniae strain or with M. flocculare. DAMPs and extracellular proteasome proteins, secreted in response to cell injury and death, were secreted by NPTr cells infected with M. hyopneumoniae 7448. All three mycoplasmas secreted virulence factors during NPTr infection, but M. hyopneumoniae 7448 secreted higher number of adhesins and hypothetical proteins, that may be related with pathogenicity. SIGNIFICANCE: The enzootic pneumonia caused by mycoplasmas of swine respiratory tract has economic loss consequences in pig industry due to antibiotic costs and pig weight loss. However, some genetically similar mycoplasmas are pathogenic while others, such as Mycoplasma hyopneumoniae and Mycoplasma flocculare, are non-pathogenic. Here, we conducted an infection assay between swine cells and pathogenic and non-pathogenic mycoplasmas to decipher secreted proteins during host-pathogen interaction. Mycoplasma response to cell infection was also observed. Our study provided new insights on secretion profile of swine cells in response to the infection with pathogenic and non-pathogenic mycoplasmas. It was possible to observe that pathogenic M. hyopneumoniae 7448 secreted known virulence factors and swine cells responded by inducing cell death. Otherwise, M. hyopneumoniae J and M. flocculare, non-pathogenic mycoplasmas, secreted a different profile of virulence factors in response to swine cells. Consequently, swine cells altered their secretome profile, but the changes were not sufficient to cause disease.

Reduction of mycoplasmal lesions and clinical signs by vaccination against Mycoplasma hyorhinis

Porcine mycoplasmal pneumonia is a significant disease problem in the swine industry. The causative agents include Mycoplasma hyopneumoniae and Mycoplasma hyorhinis. M. hyopneumoniae is the major pathogen contributing to the porcine respiratory disease complex, but is difficult to isolate from the respiratory tract and tonsils, whereas M. hyorhinis is not. Although M. hyorhinis is commonly detected in the lungs, the role of M. hyorhinis as a cause of pneumonia remains unclear. Current vaccines for porcine mycoplasmal pneumonia only include M. hyopneumoniae, not M. hyorhinis. M. hyopneumoniae vaccines are widely used, but disease still occurs because of poor vaccine efficacy and possibly the presence of M. hyorhinis. In this study, an inactivated vaccine containing a mixture of M. hyorhinis and M. hyopneumoniae was generated and evaluated for safety, immunogenicity, and protective efficacy against challenge with M. hyorhinis in pigs. The inactivated vaccine induced an antibody response and reduced pneumonic lesions in the lungs and tracheas compared with the non-vaccinated group.