Effect of the antimicrobial decapeptide KSL on the growth of oral pathogens and Streptococcus mutans biofilm.

Dental caries and periodontitis are common oral bacterial infectious diseases. Their prevention and treatment requires control of the causative pathogens, such as Streptococcus mutans and Porphyromonas gingivalis, that exist within dental plaque. As one of the attractive future substitutes for conventional antibiotics, antimicrobial peptides (AMPs), both natural and synthetic, have been widely tested and used for controlling bacterial infections. In this study, we investigated the antimicrobial activity of KSL (KKVVFKVKFK-NH(2)), a novel AMP, against several major cariogenic and periodontopathogenic bacteria as well as Candida albicans in vitro. Streptococcus mutans, the causative agent of dental caries, was chosen for in-depth testing. Bacterial susceptibility and time-kill assays were performed to investigate the sensitivity of S. mutans to KSL. The effect of KSL on biofilm formation and on pre-formed biofilm was also examined. For biofilm studies, confocal laser scanning microscopy (CLSM) was used to observe and analyse bacterial biofilm. The results showed that KSL had antimicrobial activity against a variety of oral bacteria and fungi. Streptococcus mutans and Lactobacillus acidophilus were the most susceptible strains to KSL peptide [minimum inhibitory concentration (MIC) of 0.0625 mg/mL] compared with other species tested (MICs of 0.125-1mg/mL). KSL also inhibited S. mutans biofilm formation, with a minimum biofilm inhibition concentration of 0.0625-0.125 mg/mL, and reduced 1-day-old developed S. mutans biofilm, with a minimum biofilm reduction concentration of 0.25-0.5mg/mL. CLSM images showed that KSL significantly reduced the viability of biofilm cells. This study suggests that KSL may have a potential clinical application in treating dental caries by killing S. mutans within dental plaque.