title: The role of reactive oxygen species in Staphylococcus aureus photoinactivation by methylene blue.
abstract: Methylene blue (MB) has been shown to photoinduce the direct inactivation of Gram-positive bacteria Staphylococcus aureus (S. aureus) in water. We have investigated the mechanism of S. aureus photoinactivation conducting firstly sodium azide (reactive ion N3-), as a good physical singlet oxygen quencher, then the amino acids tryptophan (Trp), as a non-specific singlet oxygen quencher and the mannitol, as an hydroxyl free radical scavenger. Inactivation of MB photosensitization is the antioxidants type dependent. When the bacteria was treated with MB (20 microM) under light during 10 min of exposure, it was found that survival fraction had decreased dramatically to about 31.27+/-5.39%. The presence of sodium azide and Trp failed to shown any protection from the MB photodynamic activity. In the presence of mannitol, S. aureus could be protected, reaching a protection level of about 27%. It is possible that the photodynamic activity of MB occurred in part, via a Type I mechanism in which *OH was produced.The interactions between MB and S. aureus were studied spectrophotometrically. This demonstrated that a metachromatic reaction took place between MB and S. aureus bacteria. Furthermore, S. aureus bacteria induced additional dimerization of MB.
authors.affiliation: National Institute of Research of Rural Engineering Water and Forestry Tunis, Rue Hédi Karray, B.P. 10, 2080, Ariana, Tunis, Tunisia. sabbahisonia@yahoo.fr
authors.forename: Sonia
authors.initials: S
authors.lastname: Sabbahi
authors.forename: Zoubeir
authors.initials: Z
authors.lastname: Alouini
authors.forename: Meryam
authors.initials: M
authors.lastname: Jemli
authors.forename: Abdellatif
authors.initials: A
authors.lastname: Boudabbous
mesh_terms: D008027:Light; D008751:Methylene Blue / Q000737:chemistry / Q000494:pharmacology*; D050296:Microbial Viability / Q000187:drug effects / Q000528:radiation effects; D010777:Photochemistry / Q000379:methods; D017382:Reactive Oxygen Species / Q000737:chemistry / Q000378:metabolism*; D013211:Staphylococcus aureus / Q000187:drug effects* / Q000378:metabolism / Q000528:radiation effects*; D013997:Time Factors
chemical_list: D017382:Reactive Oxygen Species; D008751:Methylene Blue