Characterization of antimicrobial photodynamic therapy-treated Streptococci mutans: an atomic force microscopy study.

ABSTRACT

UNLABELLED Abstract Objective: The aim of the present study was to examine the size and shape of Streptococcus mutans bacterial cells of infected dentin substrate subjected to photodynamic therapy (PDT) using atomic force microscopy (AFM). BACKGROUND DATA New trends in the application of AFM have been developed in the field of dentistry, making AFM a useful technique in high resolution imaging of biological structures and processes. MATERIALS AND METHODS: PDT was completed using an efficient light-emitting diode source (LED - λ=620-660 nm) with total light dose of 94 J/cm(2) in the presence of the photosensitizer toluidine blue O (TBO). Dentin specimens were immersed in brain heart infusion (BHI) broth inoculated with S. mutans for 5 days to induce caries in vitro. After demineralization, the samples were subjected to a series of treatments in which carious dentin infected by S. mutans was exposed to 0.9% sodium chlorite (NaCl) solution (control) for 10 min, or subjected to PDT-TBO photosensitizer followed by light exposure (energy density of 94 J/cm(2)). RESULTS: Three-dimensional (3-D) images and cross-sectional measurements showed rod and diplococcic cell shapes. Photoinactivated bacterial cells did not differ from the control with respect to their cross-sectional shape, but they did show a reduction in size. CONCLUSIONS: Photodynamic therapy decreased the diameter of S. mutans cells and AFM may be used as a technique for bacterial cell analysis.