Successful use of saliva without DNA extraction for detection of macrolide-resistant Mycoplasma pneumoniae DNA in children using LNA probe-based real-time PCR.

It is not known that saliva is useful to diagnose Mycoplasma pneumoniae ( M. pneumoniae) infection by PCR. We evaluated prospectively whether crude saliva samples without the DNA extraction process were useful for the detection of M. pneumoniae DNA in a locked nucleic acid (LNA) probe-based real-time PCR assay. Fifty-one clinical specimens (29 sputum, 22 saliva) that were positive by conventional M. pneumoniae-specific PCR were evaluated in this study. We designed an LNA probe-based real-time PCR that could discriminate the mutant strain (A2063G mutation) from the wild-type strain. All the 51 samples treated with DNA extraction were positive using the LNA probe-based real-time PCR. The results of the real-time PCR with DNA extraction were consistent with the sequence analysis. Of the 51 samples without DNA extraction, on the other hand, 41 (80.4 %) were positive by real-time PCR. Of 29 sputum samples without DNA extraction, 23 (79.3 %) were positive by real-time PCR; of the 22 saliva samples without DNA extraction, 18 (81.8 %) were positive by real-time PCR. There was a statistically significant difference in the amplified DNA levels with extraction between the direct real-time PCR-positive samples (mean ± SD, 7.5 ± 1.6 log copies/ml) and PCR-negative samples (4.2 ± 0.8 log copies/ml) ( P < 0.001). Saliva was useful for a template for PCR as well as sputum. In addition, crude samples were useful for real-time PCR when the samples had medium or high DNA levels. However, samples with low DNA levels sometimes showed false-negative results in direct real-time PCR. [ABSTRACT FROM AUTHOR]