Evaluation of the Antimicrobial Activity of Chlorhexidine and Eugenol on Planktonic and Biofilm-producing Viridans Group Streptococci Isolated from Dental Plaques

Viridnas streptococciare among the factors involved in dental caries and the subsequent diseases due to their ability in biofilm formation and the synthesis of extracellular polymers. Considering the difference in the resistance of biofilm forms and plankton pathogenic bacteria to bactericide agents, we aimed to compare the effect of chlorhexidine mouthwash and eugenol on planktonic and biofilm forms of viridnas streptococcito find the effective concentrations of the two products.
Viridans streptococci were isolated from 20 human dental plaque samples using biochemical tests. The strain with the highest biofilm formation activity was identified more precisely using 16SrRNA gene analysis. The effects of chlorhexidine (0.06-0.2 w/v%) and eugenol (29.7-99 w/v%) were assessed on the planktonic and biofilm cells of the isolated viridans streptococciusing macrodilution broth and polystyrene microplates, respectively. In addition, the minimum inhibitory concentration (MIC) of these antiseptics on the isolated viridans streptococci was determined.
Strain UTMC 2446 with 98.04% similarity to Streptococcus sanguinis had the highest biofilm production ability. The 0.2% and 99% concentrations of chlorhexidine and eugenol inhibited biofilm formation, respectively, while these compounds could effectively inhibit planktonic cell growth at the 0.14% and 79.2% concentrations, respectively.
For the tested compounds, the effective concentrations needed to inhibit biofilm formation were higher than those required for planktonic growth arrest. Moreover, due the possibility of emergence of resistant strains, as well as the fact that the required concentration is equal to the maximum concentration of the compounds in commercial products, their antimicrobial potential must be regularly monitored. Our findings can be beneficial for manufacturing and quality control facilities.