Effect of blood on lethal photosensitization of bacteria in subgingival plaque from patients with chronic periodontitis

The purpose of this study was to determine whether bacteria in subgingival plaque samples from patients with chronic periodontitis could be sensitized to killing by low-power laser light in the presence of blood. Toluidine blue O (45 μg ml⁻¹) was added to the plaque samples which were then exposed to light from a 7.3 mW HeNe laser for 30 or 120 s in the presence and absence of 10% horse blood. Viable counts of various groups and species of bacteria were determined before and after irradiation. A substantial bactericidal effect was obtained after irradiation for 30s regardless of whether or not blood was present. However, in most cases irradiation in the absence of blood resulted in greater decreases in the viable counts of aerobes, anaerobes, streptococci and blackpigmented anaerobes. When the samples were irradiated for 120s, 10% blood had little effect on the kills attained and elimination of periodontopathogenic species (black-pigmented anaerobes andFusobacterium nucleatum) was achieved both in the presence and absence of blood.