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Background Considering that the Lactobacillus casei group is strongly associated with caries progression, the use of lactobacilli as probiotics must be balanced due to their possible involvement in dental caries. Objective This study aimed to detect and quantify L. paracasei, L. rhamnosus, and L. casei group species in the active and arrested dentinal lesions of preschoolers. It also aimed to determine the expression profiles of lactobacilli genes related to adhesion, extracellular polymeric substance regulation, and pyruvate oxidation. Methods Total ribonucleic acid (RNA) was extracted from dentinal lesion samples (25 active, 13 arrested) of children between 2 and 5 years of age. The samples were converted to complementary deoxyribonucleic acid (cDNA), and quantitative polymerase chain reaction (qPCR) analyses were performed to quantify and determine the relative abundance (measured by percentage of total bacteria) of L. paracasei, L. rhamnosus, and L. casei group species. The expression profiles of L. paracasei/casei genes (spaC and spxB) and L. rhamnosus genes (spaE and wzb) were assessed. The Student t-test and the Mann-Whitney U test were used for comparisons. Results The L. casei group species were found to be part of the viable microbial community in dentinal caries. L. paracasei (p = 0.001), L. rhamnosus (p = 0.022), and L. casei (p = 0.004) group species were abundant in the active dentinal lesions compared to the arrested dentinal lesions. Only the wzb gene (p = 0.006) exhibited a statistically significant difference between the active and arrested lesions in terms of its expression profile; it was expressed to a higher extent in the active dentinal lesions. Conclusions The L. casei group species presented in large numbers in the active dentinal caries lesions, indicating that these microorganisms are related to caries activity, and the wzb gene may play an important role in caries progression.

Several studies of antimicrobial photodynamic therapy (aPDT) have been performed to verify the efficiency of this treatment against caries-related microorganisms. Thus, the aim of this study is to describe the characteristics of aPDT and to review the literature regarding its effects on cariogenic microorganisms organized in biofilms and/or caries lesions. The literature was searched for reviews and original papers about aPDT and its outcomes against Streptococcus mutans as well as other caries-associated microorganisms or caries lesions. Moreover, research on photosensitizers and light sources are also reviewed. The publications were selected using PubMed, Web of Science, and manual search of references cited in key papers. The descriptors used were "dental caries" and "photodynamic therapy". The relative efficacy of aPDT to reduce the population of cariogenic bacteria in in vitro biofilms is demonstrated by large number of laboratory studies. Preclinical (in situ models) and clinical studies show a less pronounced bacterial reduction for aPDT than for in vitro models, especially in dentin carious lesions, since the bacteria in dentin caries may be less susceptible to this therapy due to the limited photosensitizer penetration as well as reduced diffusion of light along dentin structures. Although aPDT may be an efficient and less invasive complementary approach to disinfect deep caries lesions, there is insufficient scientific evidence of its efficacy to warrant a clinical recommendation for its use.

The Bacteroides fragilis group strains colonize the intestinal tract of dogs as commensal bacteria. Nevertheless, they can be opportunistic pathogens responsible for significant morbidity and mortality rates in dogs, like in oral infections, abscesses and wound infections. The purpose of this study was to evaluate antimicrobial susceptibility in B. fragilis strains isolated from dogs intestinal microbiota and to evaluate the effect of subinhibitory concentrations of some antimicrobials on biofilm formation. A total of 30 B. fragilis group strains were tested for susceptibility to ten antimicrobial agents by broth microdilution method. Thirteen B. fragilis strains were tested for biofilm formation and the biofilm producer strains were chosen to evaluate the effect of subinhibitory concentrations of six antimicrobials on biofilm formation. The isolates were susceptible to amoxicillin-clavulanic acid, metronidazole, imipenem and chloramphenicol. Tetracycline and clindamycin were active against 50% and 33% of the strains, respectively. When biofilm-forming strains were grown in the presence of sub-MICs of imipenem and metronidazole, the inhibition of biofilm formation was observed. In contrast, enrofloxacin at ½ MIC caused a significant increase in biofilm formation in two of four strains examined. In conclusion, the B. fragilis group strains isolated were susceptible to most of the antimicrobials tested and the sub-MIC concentrations of imipenem, metronidazole and clindamycin were able to inhibit the biofilm formation.

Bacteroides fragilis colonizes dog guts both as a commensal and as an opportunistic pathogen. This study aims to evaluate virulence factors of 13 B. fragilis strains isolated from dog intestinal tracts and their ability for biofilm formation. Capsules were detected in all the evaluated strains. A total of 61.5% of all strains were biofilm producers. These attributes most likely play an important role in B. fragilis persistent colonization in the gut.