Specific PCR detection of Peptostreptococcus magnus

Objectives: Peptostreptococcus magnus is the most common and pathogenic Gram-positive anaerobic coccus in human clinical specimens. The organism has been isolated in pure culture from a range of serious infections, including meningitis and endocarditis. However, P. magnus isolation from the oral cavity has rarely been attempted. Identification of P. magnus in clinical specimens is reliant upon microbiological culture and biochemical methods, which often give ambiguous results. The aim of this study was to develop a PCR assay for the detection of P. magnus in clinical specimens.

Methods: PCR primers specific for P. magnus were derived by comparison of 16S ribosomal RNA gene sequences and selection of primers demonstrating specificity at their 3’ ends for P. magnus. PCR positivity for P. magnus was indicated by the amplification of a 553–bp product. The PCR assay was then used to attempt detection of P. magnus DNA in subgingival plaque samples from adult periodontitis patients and pus aspirates from subjects with dentoalveolar abscesses.

Results: The PCR assay was demonstrated to be highly specific for P. magnus DNA, since no PCR products were obtained when chromosomal DNA from a wide range of other oral bacteria, including closely related Peptostreptococcus species, were used in the PCR assay. The specificity of PCR products was confirmed by DNA sequencing. Of the thirty-three subgingival plaques analysed, 2 (6%) were positive for P. magnus DNA. None of the 60 pus aspirates analysed were positive for P. magnus DNA.

Conclusions: It is concluded that P. magnus is not a major pathogen in adult periodontitis and dentoalveolar abscesses. The PCR assay provides a more rapid, specific and sensitive alternative to conventional methods for identification of P. magnus in clinical specimens.