Lactobacilli Are Prominent in the Initial Stages of Polymicrobial Infection of Dental Pulp

Abstract

In earlier studies we used molecular methods to identify the major bacterial consortia associated with advanced dentin caries. These consortia are dominated by bacteria from the families Lactobacillaceae, Streptococcaceae, Veillonellaceae (formerly Acidaminococcaceae), Eubacteriaceae, and Lachnospiraceae from the phylum Firmicutes; Coriobacteriaceae, Bifidobacteriaceae, and Propionibacteriaceae from the phylum Actinobacteria; and Prevotellaceae from the phylum Bacteroidetes, as well as fusobacteria. The phases of infection of vital pulp tissue by dentin microorganisms remain obscure. In the present study, fluorescence in situ hybridization was performed on sections of tissue embedded in resin. Probes for 16S rRNA corresponding to the major taxa of bacteria in carious dentin were used to provide information on the characteristics of pulp infection. Lactobacilli were prominent in 7 of 8 pulps determined to be at a limited stage of infection. Established infection (6 pulps) showed a more complex profile, with lactobacilli persisting in all of the lesions and with invasion of the necrotic regions of tissue by Bacteroidetes, fusobacteria, Lachnospiraceae, and Coriobacteriaceae in particular. Advanced infections (7 pulps) were characterized by mixed anaerobic species, with a strong representation by Coriobacteriaceae and Lachnospiraceae. Lactobacilli were not represented at this stage. Typically, groups of organisms were spatially isolated within the pulp tissue. Analysis indicated that lactobacilli could invade vital pulp tissue to achieve a very high biomass that was not associated with a detectable local inflammatory infiltrate. The findings establish that invasion of the dental pulp can be associated with a pronounced selection from the complex microbial populations within carious dentin, suggesting specific pathogenicity.Caries progression is a protracted process involving a sequence commencing with decalcification of the enamel by organic acids produced by fermentative Gram-positive bacteria, including lactobacilli and mutans streptococci (22). Failure of the enamel barrier exposes the underlying dentin to colonization by microorganisms carried in saliva, and typically the established dentin flora is complex and variable between carious teeth (4, 16). Recent data indicate that representation of obligate anaerobes in carious dentin is greater than previously appreciated (4,8,14,15). Subsequent invasion and destruction of dental pulp provide the potential for extension of infection to adjacent bone and soft tissues.Bacteria migrate down dentinal tubules that have been damaged by organic acids produced by components of the flora. Odontoblasts that line the pulp and extend long processes into dentin were recently demonstrated to express Toll-like receptors that mediate the response of cultured odontoblasts to bacterial products (23). Odontoblasts respond to microbial insult by both deposition of new tubular dentin and deposition of mineralized intratubular plugs. More aggressive bacterial advance is considered to be...

Glial Network Responses to Polymicrobial Invasion of Dentin

“…The synchronous loss of telacyte networks and appearance of sinusoidal-like expansion of the ascending vascular loops implies, however, a degenerative change with loss of function. In relation to a potential causative mechanism, previous analysis disclosed the significance of certain species of lactobacilli in the invasion into vital pulp tissue from dentin [Nadkarni et al, 2010]. Lactobacillus rhamnosus was found to predominate, and whole genome sequencing of isolates from infected pulps [Chen et al, 2013] confirmed key differences from reference probiotic strains.…”

“…Lactobacillus rhamnosus was found to predominate, and whole genome sequencing of isolates from infected pulps [Chen et al, 2013] confirmed key differences from reference probiotic strains. These included a modified exopolysaccharide cluster characteristic of clinical isolates and that related to encapsulation of lactobacilli located deep in dentin [Nadkarni et al, 2010]. Clinical isolates were found to encode L-lactate dehydrogenase and D-lactate dehydrogenase to convert pyruvate to lactate as no lactate racemase was detected (unpublished studies).…”

Adaptive Calcified Matrix Response of Dental Pulp to Bacterial Invasion Is Associated with Establishment of a Network of Glial Fibrillary Acidic Protein+/Glutamine Synthetase+ Cells

“…Specificity for bacteria was confirmed by fluorescence ISH staining using a universal bacterial amplicon on an adjacent section. 31 In addition this pattern of staining was not observed in healthy teeth. D: Toluidine blue staining of dental pulp (from A) with the odontoblastic layer, cell-free zone, and central pulp.…”

“…Notably, accumulation of bacteria was evident at the border of physiological and reactionary dentin, while few bacteria were detected within the reactionary dentin ( Figure 1C). 31 Of these, none were detected in the inner half of the reactionary dentin and in the vicinity of the odontoblasts. The apparent resistance of reactionary dentin to bacterial insult, reflecting its modified structure, was further investigated.…”

Evaluation of cariogenic antibacterial activity of mineral trioxide aggregate and Portland cement

“…However, no previous studies have evaluated the antimicrobial activity exclusively against bacterial strains of deep decayed dentin [16][17] .…”