Antibacterial Activity of Plectranthus scutellarioides Leaf Against Actinomyces viscosus and Biocompatibility Testing on hFOB 1.19 Cell Line

Actinomyces spp. is a G+ facultative anaerobic branching bacilli that has been implicated in infections of the craniofacial, chest, and abdomen districts. Actinomyces viscosus is one of the early colonisers in the root surface and is associated with the development of caries. This study investigates the use of Plectranthus scutellarioides (L.) R.Br. leaf extract for its antibacterial properties against A. viscosus and its biocompatibility with the human foetal osteoblasts cell line (hFOB 1.19).

Activity of the lyophilized ethanolic leaf extract of P. scutellarioides was tested using the disc diffusion method followed by the determination of minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC). Bacterial morphologic changes were observed using a scanning electron microscope (SEM). In vitro, the biocompatibility of the plant extract with the hFOB 1.19 cells was investigated using the MTT assay.

An initial zone of inhibition of A. viscosus was observed with a P. scutellarioides extract concentration of 100 mg/mL and increased at an extract concentration of 200 mg/mL. The MIC50 is 1.56 mg/mL with a percentage of inhibition of 52%. At 12.5 mg/mL, the plant extract demonstrated a total bactericidal effect (MBC), whereby SEM images depicted bacterial cell wall destruction. The ethanolic extract did not exert any cytotoxic effect on the hFOB 1.19 cells at all concentrations.

Results suggest that P. scutellarioides leaf extract is a potential antibacterial agent against A. viscosus. The in vitro biocompatibility test revealed no cytotoxicity towards hFOB 1.19 cells. However, further testing is required to establish P. scutellarioides as an antibacterial agent for the prevention or treatment of periodontal disease or peri-implantitis.