In oral environments, cariogenic bacteria digest sugar and produce acid that cause tooth decays and secondary caries. A smart antimicrobial agent that activated by acid provides stimuli triggered defense systems for teeth and devices. In addition, the auto-activation of the antibacterial agent reduce the use of drug and may prevent antibiotic resistance. The objectives of this research are to synthesize and characterize a quaternary pyridinium salt (QPS) with efficient pH-sensitive antimicrobial capability, and to understand the mechanism behind it. The QPS compound was synthesized in our laboratory. It was further purified using column chromatography and recrystallization. The structure was characterized and confirmed by Nuclear Magnetic Resonance (NMR) spectroscopy and ESI (electrospray ionization)-mass spectrometry. The antibacterial activity towards S. mutans and E. coli was analyzed by planktonic MBC (minimum bactericidal concentration) values and growth curves monitoring at 3 different pH buffers. Bacteria studies showed our drug is more effective on S. mutans and E. coli in acidic than in mildly basic conditions. The switching mechanism of antibacterial activity via pH was investigated by monitoring the compound at different pH levels via NMR, UV-vis spectroscopies, DLS (dynamic light scattering), and AFM (atomic-force microscopy). We have proposed that such pH-sensitive antimicrobial activity is the result of a pH-induced self-assembly of our system, as revealed by DLS and AFM results.

pH-sensitive antimicrobial agent

254th National Meeting (2017)

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