Sensitization ofStreptococcus sanguis to killing by light from a helium/neon laser

Solutions of various photosensitizers were added to suspensions of the dental plaqueforming organism,Streptococcus sanguis. These were then exposed to light from a 7.3 mW Helium/Neon (He/Ne) laser for various time periods and the numbers of surviving cells determined by viable counting. Toluidine blue O, haematoporphyrin ester, thionin and methylene blue enabled substantial kills of the organism after irradiation times as short as 10 s which corresponds to an energy dose of 73 mJ. However, haematoporphyrin ester and, to a lesser extent, methylene blue were toxic to the organism in the absence of He/Ne light. Aluminium disulphonated phthalocyanine and crystal violet were ineffective as photosensitizers under the experimental conditions employed. The killing of sensitizedS. sanguis by light from a low-power laser suggests the possibility of a new approach to the control of dental plaque bacteria.