Expressão de genes de virulência de Streptococcus mutans em biofilme In vivo de lesões cariosas ativas e inativas de esmalte e dentina

Abstract

Streptococcus mutans is an oral pathogen considered to play a major role in dental caries development. It has been considered the most cariogenic microorganism of the oral microbiota, because it is acidogenic, tolerance to acid pH and capability of forming a firm and wellstructured three-dimensional biofilm. A better understanding of the various virulence mechanisms and the ecological role of S. mutans in the biofilm of active and inactive caries lesions may help in the development of new caries prevention strategies. The aim of this study was to investigate the S. mutans proportion in relation to total streptococci (TS) and total bacteria (TB) and the expression profile of genes related to the main virulence characteristics of S. mutans: gtfB and gtfC (adhesion); atpD, aguD, nox and fabM (acidogenicity and aciduricity) in in vivo biofilm of active and inactive caries lesions of enamel and dentin. For this, oral biofilm was collected from specific-sites from children allocated for convenience in 5 groups (n = 8): caries-free sites (CF), active enamel caries (AEC) and inactive (IEC), active dentin (ADC) and inactive (IDC) caries. Total RNA extraction, purification and cDNA synthesis were performed in all biofilm samples. Quantitative reverse transcriptase polymerase chain reactions (RT-qPCR) were performed for all samples. Data were analyzed by the Kruskal-Wallis test followed by the Dunn post-test (α = 5%). The results showed that S. mutans was detected in all samples. The SM proportion related to TS and TB quantity was significantly higher in biofilm on dentine lesions (ADC and IDC groups) (p <0.001). The gtfB gene was more expressed in the caries groups (ADC, IDC, AEC and IEC groups) when compared to the cariesfree group (CF group) (p = 0.023) while the gtfC, atpD and nox genes were expressed at higher levels in the (ADC and IDC) and caries-free (CF) groups (p = 0.001, p = 0.002 and p = 0.005). The fabM gene was more expressed in the DCA, DCI and ECI groups than in the ECA and CF groups (p = 0.004). No statistically significant differences were found in the expression of the aguD gene between the different groups (p = 0.209). It is concluded that, under the conditions evaluated, S. mutans is part of the viable microbial community of the biofilm of active and inactive lesions of enamel and dentin. The high expression of the gtfC, atpD, fabM and nox genes in dentin caries groups suggests the relationship of these genes with the progression of carious lesions, and the greater expression of the gtfB gene in the biofilm of all the carious groups suggests the relation of this gene with the presence of biofilm. The studied genes do not appear to be associated with caries activity.