A specific DNA probe for detecting Mycoplasma hyopneumoniae in experimentally infected piglets

Western Blot Immunoassay as a Confirmatory Test for the Presence of Anti-Mycoplasma Hyopneumoniae Antibodies in Swine Serum

A Western blot immunoassay (WBI) was developed as a confirmatory test for 2 commercial Mycoplasma hyopneumoniae (Mhyo) ELISAs. The WBI detected at least 5 antigen bands (150, 130, 74, 70, and 30 kDa) from Mhyo whole membrane proteins that were not present in the antigens prepared from M. hyorhinis and M. hyosynoviae. Among discrepant sera from vaccinated pigs ( n = 17) and field samples ( n = 91) assayed by WBI: 1) 2 of the ELISA-positive samples reacted with all 5 antigens bands; 2) all blocking ELISA-positive samples ( n = 53) bound 150-, 130-, 74-, and 70-kD antigen bands; and 3) all indirect ELISA-positive samples ( n = 55) bound 150-, 130-, and 30-kD antigens. We conclude that the WBI targeting the top 4 antigen bands is a useful confirmatory test for samples initially screened using the commercial Mhyo ELISAs.

Use of a Mycoplasma hyopneumoniae nested polymerase chain reaction test to determine the optimal sampling sites in swine

A number of polymerase chain reaction (PCR)-based diagnostic tests have been developed for Mycoplasma hyopneumoniae, including one from this research group. This report presents further development, optimization, and standardization of a nested PCR test. Detection sensitivity was 1 fg of M. hyopneumoniae chromosomal DNA (approximately 1 organism). This exceeded the sensitivity of or compared favorably with other published PCR tests. Polymerase chain reaction primers to porcine beta2-microglobulin were included as internal controls for amplifiable chromosomal DNA from porcine samples. To standardize the test, a number of samples from experimentally infected pigs, including nasal, tonsil, tracheobronchial swabs, lung tissue, bronchial alveolar lavage (BAL) fluid, and tracheobronchial brush samples, were examined by PCR. Samples obtained from BAL fluid and tracheobronchial sites were most predictive of infection, whereas nasal swabs and lung tissue were not reliable indicators of experimentally induced infection. In conclusion, the nested PCR developed for this study was found to be a highly sensitive and specific diagnostic tool for M. hyopneumoniae, but the enhanced sensitivity may be unnecessary if the proper sites are sampled.

Use of an internal control in a nested-PCR assay for Mycoplasma hyopneumoniae detection and quantification in tracheobronchiolar washings from pigs

We have previously reported a nested PCR assay for the detection of Mycoplasma hyopneumoniae directly in tracheobronchiolar washings from living pigs in field conditions. Here, we describe the construction and use of an internal control to monitor the presence of PCR inhibitors. A PCR modified target DNA was constructed by insertion of a small DNA fragment into the M. hyopneumoniae specific DNA target. We have demonstrated that the internal control failed to be amplified in only three tracheobronchiolar washings samples out of the 362 tested. This control molecule was inserted in a Spiroplasma citri derived plasmid vector and introduced into S. citri cells by electroporation. After a few passages we ensured that the recombinant plasmid became inserted into the genome of S. citri. PCR amplification of the DNA of this transformed S. citri strain using nested PCR primers led to amplification of a 900-bp fragment which can be discriminated from the M. hyopneumoniae PCR product 700 bp. The S. citri transformants with the integrated internal control were added to the tracheobronchiolar washings prior to PCR and used as an internal control to check the efficiency of sample processing, and to demonstrate the presence of inhibitors. Furthermore, we have been able to estimate the number of mycoplasma cells in the tracheobronchiolar washings. Quantitation was performed by comparing the PCR signal intensity of the specific M. hyopneumoniae template with known concentrations of the S. citri competitor. The titer in tracheobronchiolar washings ranged approximatively from 10(4)to 10(8)M. hyopneumoniae cells per ml of clinical specimen. Quantitative PCR can be a useful tool for monitoring the progression of M. hyopneumoniae in the disease process.

Immunoblot assays using recombinant antigens for the detection of Mycoplasma hyopneumoniae antibodies

The 36kDa L-lactate dehydrogenase (LDH) and a 29kDa partial fragment of an ABC transporter ATP-binding protein analogue/multidrug resistance protein homologue (PR2) of Mycoplasma hyopneumoniae were tested for their potential as diagnostic antigens. Recombinant LDH was genetically engineered to contain six histidine residues at its C-terminal end, expressed in Escherichia coli and purified to a high degree using Ni(2+)-chelate affinity chromatography. A partial 262 amino acid segment representing the C-terminal end of the PR2 protein was cloned as a glutathione S-transferase (GST) fusion protein, expressed in E. coli and purified by urea extraction. Purified recombinant LDH-6xHis and PR2-GST were then reacted with pig sera in immunoblot assays. Our immunoblots showed that both proteins detected anti-M. hyopneumoniae antibodies in field and experimentally infected pig sera but not in any of the SPF control sera. The two proteins were specific for M. hyopneumoniae as they did not react with sera of pigs infected with the closely related Mycoplasma flocculare and Mycoplasma hyorhinis which are frequently isolated in pigs but are not of particular concern.

Detection of Mycoplasma hyopneumoniae in bronchoalveolar lavage fluids of pigs by PCR

In the present investigation we developed a method for the detection of Mycoplasma hyopneumoniae in bronchoalveolar lavage fluid (BALF) of pigs by PCR with a primer pair flanking a DNA fragment of 853 bp specific for M. hyopneumoniae. Several methods were tested to eliminate the amplification inhibitors present in BALFs. The best results were obtained by the extraction of the DNA from the BALFs. By the PCR performed with the extracted DNA, 10(2) CFU of M. hyopneumoniae could be detected in 1 ml of BALF from specific-pathogen-free swine experimentally inoculated with M. hyopneumoniae. DNA from 11 other mycoplasma species and 17 cell-walled bacterial species colonizing the respiratory tracts of pigs was not amplified. In a field study BALFs from 40 pigs from farms with a history of chronic pneumonia were tested for M. hyopneumoniae by cultivation and by PCR (i) with BALFs incubated in Friis medium and (ii) with DNA extracted from the BALFs. In addition, PCR was performed with postmortem lung washings from 19 of the 40 pigs, and immunofluorescence tests were carried out with sections of lungs from 18 of the 40 pigs. M. hyopneumoniae could not be detected in 18 of the 40 pigs by any of the five methods tested. The remaining 22 pigs showed a positive reaction by the PCR with DNA extracted from the BALFs and variable positive reactions by the other tests. A complete correspondence could be observed between the immunofluorescence test result and the result of PCR with DNA. The investigation shows that the PCR with DNA extracted from BALFs is a suitable technique for the sensitive and specific in vivo detection of M. hyopneumoniae.