Wilson Harvey

Sensitization of oral bacteria to killing by low-power laser radiation

Twenty-seven compounds were screened for their ability to sensitizeStreptococcus sanguis to killing by light from a 7.3-mW Helium/Neon (HeNe) laser. Bacteria were mixed with various concentrations of the test compounds, spread over the surfaces of agar plates, and then exposed to light from the HeNe laser for various time periods. The plates were then incubated and examined for zones of inhibition. Those compounds found to be effective photosensitizers were then tested againstPorphyromonas gingivalis, Actinobacillus actinomycetemcomitans, andFusobacterium nucleatum. Toluidine blue O, azure B chloride, and methylene blue at concentrations of 0.005% (wt/vol) were effective photosensitizers of all four species, enabling killing of bacteria following exposure to laser light for only 30 s.

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.

A new assay for bacterial lipopolysaccharides

The purpose of this study was to ascertain whether an assay for bacterial lipopolysaccharide (LPS) could be developed based on the specific, stoichiometric binding between Polymyxin B and lipopolysaccharides. Polymyxin B was covalently linked to Sepharose 4B and the LPS-binding capacity of the resulting gel determined by incubation with various amounts of radiolabeled LPS (14C-LPS) of known specific activity. Competitive binding studies showed an inverse linear relationship between the amount of unlabeled LPS added and the binding of14C-LPS. The assay enabled the detection of microgram quantities of LPS even though the specific activity of the14C-LPS used was very low. The study demonstrated the feasibility of a Polymyxin B-based assay for LPS, and possible ways in which the sensitivity of the assay may be increased are discussed.