Detection ofMycoplasma meleagridisandM. iozvaefrom dead‐in‐shell turkey embryos by polymerase chain reaction and culture

A diagnostic polymerase chain reaction for Mycoplasma iowae using primers located in the intergenic spacer region and the 23S rRNA gene

Mycoplasma iowae is primarily a pathogen of turkeys and, although uncommon, it still persists in some areas of the world, where it may cause embryo mortality and leg lesions. A species-specific diagnostic polymerase chain reaction was developed using a forward primer based in the intergenic spacer region between the 16S rRNA and the 23S rRNA ribosomal genes and a reverse primer located within the 23S rRNA gene. The polymerase chain reaction proved to be both sensitive and specific. It detected M. iowae DNA in the six reference strains of serotypes I, J, K, N, Q and R and in 28 field isolates. With the six serotypes the test detected between 1 and 5 pg of M. iowae DNA. There were no non-specific reactions with the other avian Mycoplasma species. When the closest phylogenetically related species were checked, a weak reaction with Mycoplasma muris was observed that disappeared when the annealing temperature was increased by 2°C.

Isolation of Mycoplasma meleagridis from chickens

Mycoplasma meleagridis (MM) is a major cause of disease and economic loss in turkeys. Formerly it was thought that this species was very host specific and only restricted to turkey. In this study, we report on the recovery of MM from breeding flocks of chickens located near a turkey breeding unit. Ten MM field strains were isolated (by culture on Frey broth medium) from tracheal swabs of chickens displaying clinical signs of mycoplasmosis-essentially respiratory symptoms and poor performance. Assignment of the isolated field strains to MM was confirmed by a growth inhibition assay using MM-specific polyclonal antiserum and by PCR amplification targeting the 16S rRNA sequence as well as the Mm14 sequence, a MM-species-specific DNA fragment previously identified and characterized in our laboratory. The nucleotide sequence of Mm14 proved to be highly conserved among the 10 MM field strains, indicating a common source of infection. However, on the basis of slight differences in sodium dodecyl sulfate-polyacrylamide gel electrophoresis whole-cell proteins and western blot profiles, two groups of the isolated MM field strains could be distinguished. Evidence of MM infection of chickens was further provided by serology, since 13.77% (35/254) of sera proved positive to MM by either rapid serum agglutination or recombinant antigen-based enzyme-linked immunosorbent assay. In addition, sera of all chickens from which MM was isolated were positive for antibodies to MM. Collectively, the data unambiguously show that MM could infect chickens; thus, MM warrants further exploration to determine its pathogenicity in this unusual host.

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.

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.