Phytochemical Analysis of Plectranthus sp. Extracts and Application in Inhibition of Dental Bacteria, Streptococcus sobrinus and Streptococcus mutans

Aims: Evaluation of leaves methanol extracts from Plectranthus barbatus and Plectranthus ecklonii (Lamiaceae) against oral pathogens.

Place and Duration of the Study: P. barbatus and P. ecklonii, cultivated in Botanic Garden of the University of Lisbon, were collected during winter 2009.

Methodology: Methanol extracts were prepared and the compounds separated and identified by HPLC-DAD and mass spectrometry. The anticariogenic activity was determined by measuring the inhibition activity towards the growth of the pathogens Streptococcus mutans and S. sobrinus together with the inhibitory activity against the enzyme glucosyltransferase (GTF) involved in the biosynthesis of glucans.

Results: Phytochemical analysis of the extracts revealed the presence of two abietane diterpenoids in P. barbatus and two quinone methides together with rosmarinic acid in P. ecklonii. The two Plectranthus extracts showed bacteriostatic activity with minimum inhibitory concentrations (MIC) of 0.3 mg/mL. The minimum bactericidal concentrations (MBC) obtained for both extracts were 0.6 mg/mL against S. sobrinus and 0.8 mg/mL against S. mutans. After exposing both strains during 2h to P. ecklonii extract, 80% of inhibition against viable cells on a 24h old biofilm was observed. When methanol extracts of P. barbatus and P. ecklonii were used to inhibit the growth of the two bacterial strains in biofilm, IC50 (inhibitory concentration) values were 1.9 mg/mL and 0.57 mg/mL against S. sobrinus biofilm and 0.7 mg/mL and 0.8 mg/mL against S. mutans biofilm, respectively. P. barbatus IC50 values for the biofilm formation were 0.63 mg/mL and 0.13 mg/mL against S. sobrinus and S. mutans, respectively. P. ecklonii IC50 values for the biofilm formation were 0.07 mg/mL and 0.12 mg/mL against S. sobrinus and S. mutans biofilm. GTF from S. sobrinus was inhibited in 30% when 0.3 mg/mL of P. barbatus extract was used.

Conclusions: These extracts are important in the control of biofilms and useful in the prevention of oral diseases.