Mediterranean herb extracts inhibit microbial growth of representative oral microorganisms and biofilm formation of Streptococcus mutans

Abstract

In light of the growing antibiotic resistance, the usage of plant-derived antimicrobial agents could serve as an effective alternative treatment against oral infections. The aim of this study was to investigate the antimicrobial and antibiofilm activity of Mediterranean herb extracts against representative oral microorganisms. The extraction procedures and the analysis of the obtained extracts were performed under established experimental conditions. The minimum inhibitory (MIC) and bactericidal (MBC) concentrations of the methanol extracts of Cistus creticus ssp. creticus, Cistus monspeliensis, Origanum vulgare, Rosmarinus officinalis, Salvia sclarea and Thymus longicaulis against eight typical oral bacteria and the fungus Candida albicans were determined. The antibiofilm activity against Streptococcus mutans was also quantified using the microtiter plate test. Overall, all tested extracts inhibited effectively the screened obligate anaerobic microorganisms and in concentrations ≥0.3 mg ml-1 had moderate to high antibiofilm activity comparable to that of chlorhexidine (CHX) against S. mutans. In particular, R. officinalis (MIC: 0.08-5.00 mg ml-1) and S. sclarea (MIC: 0.08-2.50 mg ml-1) showed the highest antibacterial activity, while Cistus spp., R. officinalis and S. sclarea significantly inhibited S. mutans biofilm formation at 0.60, 1.25 and 2.50 mg ml-1, respectively. Porphyromonas gingivalis and Parvimonas micra were high susceptible to O. vulgare (MIC = 0.30 mg ml-1), whereas T. longicaulis eradicated all oral bacteria (MBC: 0.15-2.50 mg ml-1). Nevertheless, C. albicans showed no sensitivity to the tested extracts. In conclusion, the tested plant extracts could serve as alternative natural antibacterial and antibiofilm components against oral infections.

Fig 1

HPTLC chromatograms of (a) R. officinalis, (b) S. sclarea, (c) O. vulgare, (d) T. longicaulis, (e) C. creticus and (f) C. monspeliensis at 254 nm (A) and 366 nm (B) (mobile phase dichloromethane, methanol, water (70:30:4; v/v/v)).

Fig 2

HPTLC chromatograms of (a) R. officinalis, (b) S. sclarea, (c) O. vulgare, (d) T. longicaulis, (e) C. creticus and (f) C. monspeliensis at 254 nm (A) and 366 nm (B) (mobile phase ethyl acetate, methanol, formic acid, water (50:10:7:1; v/v/v/v)).

Fig 3. LC(ESI-)HRMS chromatograms of the methanol extracts of the tested plants.

Fig 4. Diagrams depicting the antibiofilm effect of six Mediterranean herb extracts against S. mutans.

The low and high cut-off OD₅₉₅ values were estimated at 0.143 and 0.428, respectively. High S. mutans biofilm inhibition is exhibited at OD₅₉₅ values ≤0.143, whereas S. mutans moderate biofilm formation is displayed at 0.143 ≤ OD₅₉₅ values ≤0.428. DMSO and CHX concentrations are shown for each extract concentration. Hash symbols and asterisks represent statistically significant differences (p < 0.01 and p < 0.05), respectively.