Identification of Lactobacilli from Deep Carious Lesions -a Comparative Evaluation

Methods: The 88 isolates were analyzed by MALDI-TOF MS (Microflex LT, MALDI Biotyper 3.0, Bruker Daltonik, Bremen, Germany), using a reference data base of 4110 strains including >90 lactobacillus species.

For the identification with species-specific PCR, oligonucleotide primer (16S rRNA) specific for L. casei, L. paracasei, L. rhamnosus, L. gasseri, L. plantarum, and L. acidophilus were used; type strains served as controls. The PCR-products were separated electrophoretically on a 1.5% agarose gel and identified by their position on the gel.

Results: By MALDI-TOF MS, 40 strains were identified as L. rhamnosus, 16 as L. paracasei ss tolerans, 16 as L. paracasei ss paracasei, 6 as L. paracasei, 3 as L. gasseri, 2 as L. plantarum, 2 as L. parabuchneri, 2 as L. spec., and 1 strain could not be identified.

By species-specific PCR, 42 strains were identified as L. rhamnosus, 16 as L. paracasei ss tolerans, 16 as L. paracasei ss paracasei, 5 as L. paracasei, 1 as L. casei, 3 as L. gasseri, 2 as L. plantarum; 3 strains could not be identified.

For 92% of the strains both methods produced concordant results, in 4.5% the results were discordant. Of the remaining 3 strains, not identified by species-specific PCR, 1 strain was identified by MALDI-TOF MS as L. spec. and 1 as L. parabuchneri. One strain couldn’t be identified by either method.

Conclusions: Both methods are highly sensitive. Limitations can be the precision of the primers (PCR) or the scarcity of strains from a certain habitat in the data base. Additional information is necessary for the strains without or with discordant identification.