Antibacterial Activity of Nigella sativa Seed Oil Against Oral Pathogens and Its Inhibitory Effects on Acid Production and Biofilm Formation in Streptococcus mutans

This study was conducted to investigate the antibacterial activity of Nigella sativa seed oil (HT_01) against several oral pathogens and the inhibitory effects of HT_01 on acid production and biofilm formation in Streptococcus mutans. The antibacterial activity of HT_01 was tested using the disk diffusion and microdilution methods according to Clinical & Laboratory Standards Institute and Korean Ministry of Food and Drug Safety guidelines. The acid-producing ability test and biofilm formation ability were performed according to Korean Ministry of Food and Drug Safety guidelines. The inhibition zone around the disks containing 50 μL of 10% HT_01 were 42.5 ± 2.5 mm for S. mutans, 41.4 ± 4 mm for Porphyromonas gingivalis, 45 ± 3 mm for Prevotella intermedia, and 28 ± 3 mm for Fusobacterium nucleatum, indicating a strong antibacterial effect. Analysis of acid production showed that the pH of culture broth of S. mutans was 4.23 ± 0.05, whereas culture broth containing of 0.04% and 0.05% HT_01 had neutral pH values of 7.35 ± 0.02 and 7.21 ± 0.04, respectively, confirming the inhibition of acid production. Compared with the control group considered as showing 100% biofilm formation, the rate of biofilm formation was only 32% in the presence of 0.05% HT_01. HT_01 showed potent antibacterial activity against oral pathogens. HT_01 showed potent inhibitory activity against acid production and biofilm formation in S. mutans.