Abstract
Streptococcus mutans is a well-known oral pathogen commonly associated with a normal dental problem and life-threatening infection. A bacteriocin nisin and the plant-derived compounds including gallic acid (GA) and Thai culinary essential oils (EOs) have been reported to have activity against oral pathogens. However, their synergistic interaction against S. mutans has not been explored. The purposes of this study were primarily to investigate anti-S. mutans properties and the antibiofilm formation of nisin, GA, and five EOs by using the broth microdilution method. Besides, the morphological change, killing rate, and antibacterial synergism were determined by scanning electron microscopy (SEM), time-kill assay, and checkerboard method, respectively. The results demonstrated that kaffir lime leaf (KLL) oil, lemongrass (LG) oil, and GA showed a potent anti-S. mutans activity and inhibited biofilm formation with the possible mechanism targeted on the cell membrane. Additionally, KLL oil revealed anti-S. mutans synergism with GA, LG oil, and chlorhexidine with the fractional inhibitory concentration (FIC) indexes ≤ 0.5. Interestingly, GA displayed a high potential to enhance anti-S. mutans activity of nisin by lowering the minimum inhibitory concentrations (MICs) to at least 8-fold in a bacteriostatic manner. These results suggest that GA and KLL oil may be potentially used as an adjunctive therapy along with nisin and chlorhexidine to control S. mutans infection.
Highlights
A Gram-positive streptococcal bacterium, S. mutans, is an important oral pathogen that can cause common dental caries in humans and life-threatening infectious diseases such as infective endocarditis after entering the blood circulation [1]
To prevent the dental problems and the resulting complication, dental hygiene is necessary throughout the human lifespan [2, 3]. e virulence determinant produced by S. mutans is the formation of cariogenic biofilms or dental plaques, which protect the sessile bacteria from antibacterial compounds. erefore, potential strategies to combat S. mutans are the inhibition of biofilm development and eradication planktonic cells [4]
Terpenes and terpenoids were the major constituent found in FR (Δ-3-careen, 24.4%), KL (L-limonene, 25.1%), and kaffir lime leaf (KLL) oils, whereas lactone (c-dodecalactone, 33.1%) was mainly found in LG oils
Summary
A Gram-positive streptococcal bacterium, S. mutans, is an important oral pathogen that can cause common dental caries in humans and life-threatening infectious diseases such as infective endocarditis after entering the blood circulation [1]. E virulence determinant produced by S. mutans is the formation of cariogenic biofilms or dental plaques, which protect the sessile bacteria from antibacterial compounds. Mechanical cleaning is an effective approach to remove the cariogenic species and biofilms, the chemical antibacterial agents have been beneficially added to many oral healthcare products for similar purposes [5]. Nisin produced by safe lactic acid bacteria species Lactococcus lactis effectively inhibits food-borne pathogens in both vegetatively growing cells and spores of Clostridium botulinum and Bacillus cereus [10, 11]. This bacteriocin does not change the organoleptic properties of foods [12]. Sangcharoen et al.[16] reported that the antibacterial activity of nisin could be enhanced by weak organic acids such as ascorbic acid and citric acid
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
