The role of members ot the genus Lactobacillus in the development and progression of caries is a single facet of a multifactorial disease. The use of lactobacilli counts in the prediction of caries was implemented as tool in clinical studies since 1930, but relatively few references to the specific species of oral lactobacilli and their specific role during cariogenesis were made. Because of subjectivity of existing classification systems for lactobacilli, this in-depth study on the taxonomical position of oral lactobacilli in the genus Lactobacillus was carried out. Three study groups were used in the study, namely 3-6 year old toddlers with primary dentition, 9 year old children with mixed primary and secondary dentition and 13 year old children with secondary dentition. During clinical evaluation of all children data for caries prediction were gathered and stimulated saliva samples were collected for isolation of oral lactobacilli. Conventional identification and grouping of isolates by SDS-PAGE were investigated to indicate the ecological diversity of the species and to clarify the status of oral lactobacilli in the genus Lactobacillus. During the onset of the study it was realized that collection of research data which are used for caries prediction in the first world (Europe and the USA) are not necessarily applicable and relevant for the South African mixed first and third world environment, as diet, culture and traditions of these worlds differ vastly. Nevertheless, positive correlation between lactobacilli counts in saliva and caries (dmft/DMFT) confirmed the value of lactobacilli counts as predictive factor. Positive correlation between flow rate and buffering capacity of saliva indicated that other factors are important in caries prediction and confirmed that caries is a multifactorial disease. Positive correlation between prevalence of lactobacilli and caries incidence indicated that prevalence of lactobacilli can possibly be used as single caries indicator. The collection of a variety of lactobacilli from the oral cavity confirmed that existing literature and research results are inadequate to describe the species within the oral cavity habitat and the role of these organisms during cariogenesis is not defined. Conventional taxonomy indicated a selection for predominance of homofermentative species and indicated that the species composition change with changes in age and dentition status. The homof ermentative species from toddlers were dominated by L. paracasei and as soon as the dentition status of the children changed to a mixed and secondary dentition, L. paracasei, L. rhamnosus and L. casei were dominant. The heterofermentative species of toddlers were not dominated by a specific species, and as soon as the dentition status changed to mixed and secondary dentition, the species were dominated by L. fermentum. Although these dominant species of oral lactobacilli was identified, variations in tests for identification occurred and it was not possible to compare results with type species of the organisms, as most of the described type species originate from habitats other than the oral cavity. Species classification by conventional identification methods did not agree with grouping of isolates with SOS-PAGE, and grouping of oral lactobacilli did not correlate with type strains of species. This finding confirms the existence of groups of oral organisms different from the type species of Lactobacillus. The groupings of the oral isolates did not change when the borders of the GELCOMP AR 3 program were changed, this confirmed the reliability of the high correlation coefficient found between groups of oral lactobacilli. The defined groups of isolates should be used for the development and application of polyphasic classification systems which consider phenotypical, phylogenetic, genotypic, biochemical and enzymatic properties to describe the oral lactobacilli. Such descriptions will clarify the specific status of the oral lactobacilli in the genus Lactobacillus and will facilitate the description of type species of oral lactobacilli which in turn will broaden knowledge on the role and activity of oral lactobacilli in cariogenesis and may result in new species being created.
Thesis (PhD (Mikrobiologie))--University of Pretoria, 1996.