A novel species-specific PCR assay for identifying Lactobacillus fermentum

Lactobacillus fermentum is a Gram-positive bacterium that is associated with active caries lesions. Methods for identifying Lactobacillus species traditionally have been based upon culture methods coupled with biochemical tests, which are generally unreliable. The aim of this study was to develop a species-specific PCR assay for the direct detection of L. fermentum in oral clinical samples. PCR primers specific for L. fermentum were identified by alignment of bacterial 16S rRNA genes and selection of sequences specific for L. fermentum at their 3' ends. PCR positivity for L. fermentum DNA was indicated by amplification of a 337 bp product. The primers were shown to be specific for L. fermentum DNA, since no PCR product was obtained when genomic DNA from a wide range of other oral bacteria, including closely related Lactobacillus species, were used as test species. The PCR assay was then used in an attempt to identify L. fermentum DNA in supragingival plaque samples and in pus aspirates from subjects with acute dento-alveolar abscesses. Four out of 70 (5.7 %) supragingival plaque samples analysed were positive for the presence of L. fermentum DNA while none of the 19 pus samples analysed was positive for L. fermentum DNA. This PCR assay provides a more rapid, specific and sensitive alternative to conventional culture methods for the identification of L. fermentum in clinical specimens.