Effect of photoactivated disinfection using light in the blue spectrum

•LED emitting in the blue spectrum combined with riboflavin acts antibacterial.•LED in the red spectrum combined with toluidine blue is superior.•Multi-species biofilms are not sensitive to photoactivated disinfection using LED.

BackgroundLight in the blue spectrum is well known to cure composites. This in vitro-study was aimed to analyze a potential antimicrobial activity when combined with riboflavin as a photosensitizer.MethodsPhotoactivated disinfection (PAD) using a LED lamp emitting in the blue spectrum for 30 s (PAD30) and 60 s (PAD60) after application of 0.1% riboflavin was compared with a LED lamp emitting in the red spectrum with the respective photosensitizer (PADred). Killing activity was analyzed against planktonic 14 single species and a 12-species mixture with and without 25% serum. In addition, there was a reduction of viable bacterial counts in single species and a 12-species biofilm was measured after PAD.ResultsGram-positive bacteria were less sensitive to PAD30 and PAD60 than Gram-negatives. PAD60 decreased the counts by more than 3 log10 cfu in two of five Gram-positive and in six of nine Gram-negative strains, the total viable counts of the mixture were reduced by 1.04 ± 0.46 log10 cfu. In the presence of 25% serum a decrease by more than 2 log10 cfu was only found in tests with one Porphyromonas gingivalis strain. PADred killed all included strains except for the 12-species mixture and Eubacterium nodatum. PAD60 reduced the counts in P. gingivalis biofilms by 2–3 log10 cfu, however there was no activity of PAD60 and PADred on the multi-species biofilm.ConclusionsPAD using LED emitting in the blue spectrum combined with riboflavin is active against periodontopathogenic microbial species but clearly inferior to PADred. Multi-species biofilms are not sensitive to PAD using LED.