The investigation of synergistic activity of protamine with conventional antimicrobial agents against oral bacteria

Abstract In this study, we applied protamine, which is an antimicrobial peptide, to oral healthcare in combination with conventional antimicrobial agents. First, we explored the antimicrobial activity of protamine, with or without other antimicrobial agents, against Streptococcus mutans (S. mutans). Co-treatment with protamine and 3-methyl-4-isopropylphenol (IPMP) decreased the viability of S. mutans synergistically within 10 min. Interestingly, sodium fluoride (NaF) did not exhibit synergistic activity with protamine. Next, S. mutans and Streptococcus gordonii (S. gordonii) were co-treated with protamine and IPMP for 5 min to simulate tooth brushing. As a result, this co-treatment killed S. mutans faster than S. gordonii. Therefore, co-treatment with protamine and IPMP could be incorporated into oral healthcare products to prevent dental caries.