Biofilm formation a pioneer step of dental caries

Dental plaque has been discussed as a biofilm (figure 1). Donlan and Costerton (2002) presented the most relevant description of a biofilm.

Fig. 1. Colored scanning electron micrograph of dental plaque (Streptococcus mutans bacteria are pink).

They declared that a biofilm is "a microbially derived sessile community characterized by cells that are attached to a substrate or to each other, are embedded in a matrix of extracellular polymeric substances that they have produced, and exhibit an altered phenotype with respect to growth rate and gene transcription."

A biofilm is structured to maximize energy. Degree of organization and multispecies organization characterize the four stages of biofilm growth (Figure 2). There are four stages in the lifecycle whether the organism is planktonic or as member of a biofilm. Stage I is the inactive or least metabolically active state. Transformation from Stage I to Stage II needs significant genetic up-regulation. Stage III involves maturity of the biomass, and total organism concentration can come near 1011 or 1012 colony-forming units per milliliter. At this phase, new antigens may be expressed, genetic exchange enhanced and membrane transport maximized. Stage IV (apoptosis or death) signals detachment or sloughing from the biofilm (Donlan & Costerton, 2002; Thomas et al., 2006).

Fig. 2. Four stages of dental plaque biofilm growth: Stage I attachment (lag [not inert, but metabolically reduced]), Stage II growth (log [exponential growth]), Stage III maturity (stationary) and Stage IV dispersal (death) ( Thomas et al 2006).

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