Comment on “Effectiveness of antimicrobial photodynamic therapy (AmPDT) on Staphylococcus aureus using phenothiazinecompound with red laser”

Excerpt

After reading the following paper: “Effectiveness of antimicrobial photodynamic therapy (AmPDT) on Staphylococcus aureus using phenothiazine compound with red laser” Monteiro, J.S.C., de Oliveira, S.C.P.S., Pires Santos, G.M. et al. Lasers Med Sci (2016). doi:10.​1007/​s10103-016-2079-4, I would like to make a comment as to the method of calculating AmPDT treated bacteria. Phenothiazinium photosensitizers have been studied in the field of antimicrobial photodynamic research for years [1‐4]. The most frequently studied Methylene Blue and Toluidine Blue showed light-enhanced antimicrobial efficacy towards Gram-positive and Gram-negative species. To properly assess the effectiveness of antimicrobial compound, calculating the log₁₀ reduction from the initial number of CFU/ml are typically performed. Based on general guidelines of the American Society for Microbiology reduction the number of bacteria at least 3 log₁₀ CFU/ml is considered biologically relevant [5]. In the paper by Monteiro et al., only 2 log₁₀ reduction was observed, which is not considered antibacterial action. …