Identification of salivary Lactobacillus rhamnosus species by DNA profiling and a specific probe

The Lactobacillus genus has been shown to be associated with the dental car ious process, but little is known about the species related to the decay, a lthough Lactobacillus rhamnosus is suspected to be the most implicated spec ies. Conventional identification methods based on biochemical criteria lead to ambiguous results, since the Lactobacillus species found in saliva are phenotypically close. To clarify the role of this genus in the evolution of carious disease, this work aimed to find a rapid and reliable method for i dentifying the L. rhamnosus species. Methods based on hybridization with DN A probes and DNA amplification by PCR were used. The dominant salivary Lact obacillus species (reference strains from the ATCC) were selected for this purpose as well as some wild strains isolated from children's saliva. DNA p rofiling using semirandom polymorphic DNA amplification (semi-RAPD) generat ed specific patterns for L. rhamnosus ATCC 7469. The profiles of all L, rha mnosus strains tested were similar and could be grouped; these strains shar ed four common fragments. Wild strains first identified with classic method s shared common patterns with the L. rhamnosus species and could be reclass ified. One fragment of the profile was purified, cloned, used as a probe an d found to be specific to the L. rhamnosus species. These results may help to localize this species within its ecological niche and to elucidate the p rogression of the carious process. (C) 2001 Editions scientifiques et medic ales Elsevier SAS.