Species-specific oligonucleotide probes complementary to 16S rRNA of Mycoplasma gallisepticum and Mycoplasma synoviae

Experiences with multispecies polymerase chain reaction and specific oligonucleotide probes for the detection of Mycoplasma gallisepticum and Mycoplasma synoviae

Amplified fragments of the rDNA coding for 16S rRNA of Mycoplasma gallisepticum (MG) and Mycoplasma synoviae (MS) were blotted on nylon membranes, followed by dot-blot detection with two species-specific digoxigenin-(DIG)-labeled oligonucleotide probes. The sensitivity and specifity of the tests were determined in titration studies with purified homologous and heterologous DNA. With the detection protocol used, the MSYV8/31 probe showed 100% specifity for MS, while both MG and the related species Mycoplasma imitans were recognized by the MGAV8/31 probe. Both DIG-labeled oligonucleotides gave positive results in the colorimetric assay with 10 to 100 ng homologous non-amplified DNA and polymerase chain reaction (PCR) amplificates of 100 fg homologous template DNA. There was no reaction with heterologous strains when amplificates starting with a 106-fold amount of template DNA (100 ng) were tested in dot-blots. The suitability for field samples was demonstrated with tracheal swabs from turkeys and chickens, and the results were compared with mycoplasma growth in cultures of the same swabs. Both tests had an accuracy of over 95%, a high sensitivity and specificity, and high predictive values of positive or negative results. There was no significant difference between the results obtained by the two methods. PCR in combination with dot-blotting is a relatively simple method for the detection of mycoplasma infections, and a valuable extension of current diagnostic tools.

Development of a loop-mediated isothermal amplification targeting a gene within the pyruvate dehydrogenase complex, the pdhA gene, for rapid detection of Mycoplasma gallisepticum

Mycoplasma gallisepticum infections impose a significant economic burden on the poultry industry. In the current study, a loop-mediated isothermal amplification (LAMP) assay was developed and optimized to detect M. gallisepticum based on a gene within the pyruvate dehydrogenase complex, the pdhA gene, which codes for the major subunit (E1α) in the complex. The reaction conditions were optimized, and the specificity was confirmed by successful amplification of several M. gallisepticum strains, while no amplification was detected with 20 other major bacterial and viral pathogens of poultry. Additionally, the LAMP assay achieved 10-fold higher sensitivity than an existing polymerase chain reaction (PCR) method. The LAMP assay was applied to swab samples collected from poultry farms and compared with PCR. The positive detection rate was 20.2% (37/183) by LAMP and 13.1% (24/183) by PCR. The LAMP assay could provide a cost-effective, quick, and sensitive method for the detection of M. gallisepticum.

Real-time polymerase chain reaction for the qualitative and quantitative detection ofMycoplasma gallisepticum

The aim of this study was to evaluate the sensitivity and the detection limit of a real-time polymerase chain reaction (Q-PCR) developed for the qualitative and quantitative detection of Mycoplasma gallisepticum. No cross-reactivity was observed with DNA from other important avian mycoplasmas, including Mycoplasma synoviae and Mycoplasma meleagridis. However, the Q-PCR could not distinguish between M. gallisepticum and Mycoplasma imitans. The Q-PCR had detection limits 10 to 1000 times lower than a conventional commercial PCR method and than culture. The Q-PCR was used quantitatively by incorporating a set of external M. gallisepticum DNA standards, derived from a M. gallisepticum log-phase culture of a known concentration. The number of colony-forming unit equivalents per millilitre in tracheal swabs from experimentally infected birds could be determined from a single sample. The method had good reproducibility and correlated well with standard counting techniques using culture. It can be concluded that the Q-PCR described is suitable for qualitative and quantitative detection of M. gallisepticum in clinical samples.

Comparison of Culture, PCR, and Different Serologic Tests for Detection of Mycoplasma gallisepticum and Mycoplasma synoviae Infections

In this study, the technical performance of culture, two commercially available polymerase chain reaction (PCR) tests, rapid plate agglutination (RPA) test, hemagglutination inhibition (HI) test, and eight commercially available enzyme-linked immunosorbent assays (ELISAs) were compared for the detection of avian mycoplasma infections from 3 days postinfection (d.p.i.) through 35 d.p.i. The tests were carried out on samples from specified pathogen-free layers that were infected at 66 wk of age with recent Mycoplasma synoviae (MS) and Mycoplasma gallisepticum (MG) field strains, MS and MG ATCC strains, and Mycoplasma imitans (MIM), respectively. Results showed a high percentage of positive samples in the homologous infected groups and a high percentage of negative samples (100%) in the uninfected and heterologous infected groups during 35 d.p.i. of both culture and PCR tests. For the group infected with the MG 15302 ATCC strain, serology was more sensitive than bacteriology. All MG and MS tests, with the exception of MG ELISA kit D showed a lower percentage of positive samples during 35 d.p.i. for the detection of the MG and MS ATCC strain infection compared with that of the field strains. Also, the number of cross-reactions (false positives) in the serologic tests was lower after infection with an ATCC strain than after an infection with the MG or MS field strain. Contradictory to other studies, the ELISAs and the RPA test using undiluted serum showed a relatively high number of false-positive results. The MG ELISAs (except ELISA kit D) showed more false-positive results (up to 37%) in the MIM-infected group than in the MS-infected groups. This was not unexpected, as MIM and MG have a close antigenic relationship. The results of the serologic tests in this study showed that a certain level of false-positive results can be expected in about any serologic test. Although the level of false-positive results varied between several serologic tests, this study showed that it is not advisable to rely completely on one test (system) only.

Use of an alkaline phosphatase-labelled probe for the detection of Mycoplasma synoviae in chickens

Short nucleotides directly labelled to alkaline phosphatase (SNAP probes) are an interesting alternative to digoxigenin-labelled probes (DIG probes), because they reduce the number of steps necessary in dot blots for the detection of DNA or amplificate. This study examined the questions whether a SNAP probe might not only save time, but also increase the sensitivity of another PCR-based DNA probe test using a digoxigenin probe. Amplificates obtained by multispecies polymerase chain reaction (PCR), with either purified genomic DNA or DNA extracted from tracheal swabs taken in chicken flocks, were detected by both methods. The results for the clinical specimens were compared to culture. Under stringent conditions, the specificity and sensitivity obtained with the SNAP probe were comparable to the results obtained with the DIG probe. The quantities 10 fg (SNAP probe) and 100 fg (DIG probe) of purified Mycoplasma synoviae DNA were detected after amplification, but more positive clinical specimens were detected with the DIG probe. Under non-stringent conditions sensitivity with purified DNA did no change, but the coloration of the dots improved markedly, and more positive specimens could be detected with the SNAP probe than with the DIG probe, truly positives as confirmed by culture. Because cross-reaction with Mycoplasma gallisepticum and Mycoplasma imitans, two species with DNA that was also recognized by the multispecies primers, occurred under non-stringent conditions, it was concluded that, to take the full advantage of SNAP probes, their use in combination with species-specific primer pairs is recommended. PCR as a method for mycoplasma detection is however, always accompanied with serological and cultural methods. When a M. synoviae mono-infection is likely by serological results, non-stringent dot blot conditions and use of the SNAP probe will ease and improve the detection of mycoplasma.

Detection and identification of avian mycoplasmas by polymerase chain reaction and restriction fragment length polymorphism assay

The polymerase chain reaction (PCR) with primers complementary to the 16S rRNA genes was used to detect avian mycoplasmas. A primer pair designed for the detection of human and rodent mycoplasmal species was examined for its ability to detect the most important avian mycoplasmas. After testing the respective reference strains, we found that Mycoplasma iowae, Mycoplasma meleagridis and Mycoplasma synoviae could be detected by PCR with this primer pair, and distinction could be made among them by restriction fragment length polymorphism (RFLP) assay with two restriction enzymes (BamHI and RsaI). For the detection of Mycoplasma gallisepticum by PCR, we needed species-specific primers. The results of the PCR- and RFLP, based identification procedures of 17 different field isolates agreed with those obtained by conventional methods.

Use of species-specific oligonucleotide probes to detect Mycoplasma gallisepticum, M. synoviae, and M. iowae PCR amplification products

Three digoxigenin-labeled oligonucleotide probes, complementary to the variable region of the 16S ribosomal RNA (rRNA) gene of Mycoplasma gallisepticum, M. synoviae, and M. iowae were designed. The oligonucleotides were used in a dot blot hybridization assay. The target DNA is a 780-bp fragment of the 16S rRNA gene of avian mycoplasmas amplified by a single set of primers (multispecies polymerase chain reaction [PCR]). The oligonucleotide probes were specific for their corresponding PCR products at hybridization conditions of 56 C and 50% formamide. The detection limit of the dot blot hybridization assay was approximately 70, 50, and 30 colony-forming units for M. gallisepticum, M. synoviae, and M. iowae, respectively, per 4 microliters of PCR. In general, the oligonucleotide probe dot blotting assay was a more sensitive and effective method of detecting PCR products than detection by gel electrophoresis.