Biomedical subjects
Publications and source records attributed to J Pratten.
Using a constant-depth film fermentor, we have grown a six-membered biofilm community with a bacterial composition similar to that found in supragingival dental plaque. Cryosectioning revealed the distribution of bacteria throughout the biofilm. Exposure to 0.2% chlorhexidine for up to 5 min had little effect on biofilm viability.
The aim of this study was to determine whether Streptococcus sanguis, when in a biofilm, could be killed using a light-activated antimicrobial agent. Biofilms were grown on hydroxyapatite, irradiated with up to 12.2 J of light from a gallium aluminium arsenide laser in the presence of aluminium disulphonated phthalocyanine (AlPcS2) and survivors enumerated. No significant decrease in the viable count was found when either the AlPcS2 or the laser light was used alone. There was a light dose related decrease in the viable counts of irradiated AlPcS2-treated biofilms. No viable streptococci were detectable following irradiation with 12.2 J of laser light.
BACKGROUND AND OBJECTIVES: Staphylococcus aureus can be killed by low-power laser light in the presence of aluminium disulphonated phthalocyanine (AlPcS2). The purpose of this study was to determine the effect of pre-irradiation time (PIT), the presence of serum, and the physiological state of the organism on the kills achieved. STUDY DESIGN/MATERIALS AND METHODS: To determine the effect of PIT on killing, suspension of methicillin-resistant S. aureus (MRSA) were incubated in the dark with 12.5 micrograms/ml of AlPcS2 for 60 s or 300 s, and survivors were enumerated after exposure to 1.2 J of light from an 11-mW gallium aluminium arsenide laser. The susceptibility of MRSA in its various growth phases was determined in a similar manner using a PIT of 300 s. The effect of serum on killing was determined using stationary phase cells resuspended in horse serum. RESULTS: Using a PIT of either 60 s or 300 s, 10(6) cfu (99.9%) of MRSA were killed. There was little difference in the susceptibility of lag-, logarithmic-, or stationary-phase cells, the kills being 99.9%, 99.8%, and 99.9%, respectively. Although kills were reduced in the presence of serum, 99.6% of MRSA were killed using a light dose of 1.2 J. CONCLUSION: These results demonstrate that MRSA can be rapidly sensitised by AlPcS2 to killing by low-power laser light, that killing is not dependent on the organism's growth phase, and that substantial kills can be achieved in the presence of serum.
The purpose of this study was to determine whether bacteria in supragingival plaque samples could be killed by low-power laser light in the presence of a suitable photosensitizer. Plaque samples were obtained from 10 volunteers, treated with either toluidine blue O (TBO) or aluminum disulphonated phthalocyanine (AlPcS2), and then exposed to light from a helium/neon (HeNe) or gallium aluminium arsenide (GaAs) laser respectively. Following irradiation, substantial reductions were achieved in the total anaerobic count as well as in the number of viable streptococci and actinomyces present in the samples. In the absence of laser light, the sensitizers themselves had little effect on the viability of the bacteria in the plaque samples. The HeNe/TBO combination appeared to be more effective than the GaAs/AlPcS2 combination, achieving log10 reductions of 2.95, 5.40 and 3.34 in the total anaerobic count, streptococci and actinomyces respectively with a light energy dose of 1.31 J. If effective in vivo, lethal photosensitization may be useful as a means of eliminating plaque bacteria from a carious lesion prior to its restoration.
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The purpose of this study was to determine whether toluidine blue O (TBO) could sensitise Staphylococcus aureus to killing by light from a low-power helium/neon (HeNe) laser. Suspensions of the organism were irradiated with light from a HeNe laser in the presence and absence of TBO and the survivors enumerated. A 95% reduction (9 x 10(7) cfu) in the viable count was achieved following irradiation with 0.88 J of HeNe laser light in the presence of 12.5 micrograms/ml TBO whereas no significant reductions in viability were found when suspensions were exposed to this dose of laser light in the absence of TBO. With higher doses (3.5 J) of laser light statistically significant kills (3 x 10(7) cfu) were obtained in the absence of TBO implying the presence of an endogenous photosensitiser in the organism.
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