Diversity of Lactobacillus species in deep carious lesions of primary molars

This was to determine the prevalence of Lactobacilli (LB) species in different stages of caries progression and are considered as secondary invaders of existing carious lesions and specialists for caries progression.

Carious dentine samples were collected from 70 primary molars (M) during step-wise (S1, S2: n = 35 M) or one-step (O1: n = 35 M) caries treatment and after 11 months of temporary restorations (S3, O2). LB were identified by selected physiological and biochemical characteristics, ratio of lactic acid isomers, electrophoretic mobilities of lactic acid dehydrogenases, and shotgun mass mapping by MALDI mass spectrometry.

LB were isolated from 46% of soft dentine samples (S1). The prevalence of LB from hard dentine collected during caries excavation (O1) reached 34%, after 8 weeks of temporary filling (S2) 11%, and 9% each after 11 months of temporary restoration (S3, O2). The mean total bacterial counts (cfu) of soft dentine (S1) were 3.6 x 10⁵. From hard dentine during caries excavation (O1) 4.4x10⁴ cfu were calculated, at S2 3.7 x 10³ cfu, at S3 0.1 x 10³ cfu, and at O2 1.8 x 10³ cfu. The percentages of LB in the cfu for LB positive dentine samples were for S1 / S2 / S3 / O1 / O2: 60% (16 M)/34% (4 M)/54% (3 M)/57% (9 M), and 64% (3 M). Five LB species were identified from carious dentine: L. paracasei subsp. paracasei, L. paracasei subsp. tolerans, L. rhamnosus, L. gasseri, and L. alimentarius.

While L. rhamnosus and L. paracasei subsp. paracasei occurred in all caries progression stages, the other species were found only sporadically. L. paracasei subsp. paracasei and L. rhamnosus might be the specialists of the LB in carious progression.