Photodestruction of human dental plaque bacteria: Enhancement of the photodynamic effect by photomechanical waves in an oral biofilm model

Background and Objectives: Periodontal disease results from the accumulation of subgingival bacterial biofilms on tooth surfaces. There is reduced susceptibility of these biofilms to antimicrobials for reasons that are not known. The goals of this study were to investigate the photodynamic effects of a conjugate between the photosensitizer (PS) chlorin(e6) (c(e6)) and a poly-L-lysine (pL) with five lysine residues on human dental plaque bacteria as well as on biofilms of the oral species Actinomyces naeslundii after their exposure to photomechanical waves (PW) generated by a laser in the presence of the conjugate. Study Design/Materials and Methods: Subgingival plaque samples from 12 patients with chronic destructive periodontitis were divided in 3 groups that were incubated for 5 minutes with 5 muM c(e6) equivalent from the pL-c(e6) conjugate in the presence of fresh medium (group 1), PBS (group II), and 80% PBS/20% ethylenediaminetetra-acetic acid (EDTA) (group 111) and were exposed to red light. Also, biofilms of A. naeslundii (formed on bovine enamel surfaces) were exposed to PW in the presence of 5 muM c(e6) equivalent from the pL-c(e6) conjugate and were then irradiated with red light. The penetration depth of the conjugate was measured by confocal scanning laser microscopy (CSLM). In both cases, after illumination serial dilutions were prepared and aliquots were spread over the surfaces of blood agar plates. Survival fractions were calculated by counting bacterial colonies. Results: The PS/light combination achieved almost 90% killing of human dental plaque species. In biofilms of A. naeslundii, CSLM revealed that PW were sufficient to induce a 50% increase in the penetration depth of the pL-c(e6) conjugate into the biofilm. This enabled its destruction (99% killing) after photodynamic therapy (PDT). Conclusions: PW-assisted photodestruction of dental plaque may be a potentially powerful tool for treatment of chronic destructive periodontal disease. (C) 2003 Wiley-Liss, Inc.