title: Rationale and mechanism for the low photoinactivation rate of bacteria in plasma.
abstract: The rate of bacterial photoinactivation in plasma by methylene blue (MB), especially for Gram-negative bacteria, has been reported to be lower, by about an order of magnitude, than the rate of inactivation in PBS and water solutions. This low inactivation rate we attribute to the bleaching of the 660-nm absorption band of MB in plasma that results in low yields of MB triplet states and consequently low singlet oxygen generation. We have recorded the change of the MB 660-nm-band optical density in plasma, albumin, and cysteine solutions, as a function of time, after 661-nm excitation. The transient triplet spectra were recorded and the singlet oxygen generated in these solutions was determined by the rate of decrease in the intensity of the 399-nm absorption band of 9, 10-anthracene dipropionic acid. We attribute the bleaching of MB, low singlet oxygen yield, and consequently the low inactivation rate of bacteria in plasma to the attachment of a hydrogen atom, from the S-H group of cysteine, to the central nitrogen atom of MB and formation of cysteine dimer.
authors.affiliation: Key Laboratory for Laser Plasmas (Ministry of Education) and Department of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240, China.
authors.forename: Jie
authors.initials: J
authors.lastname: Chen
authors.forename: Thomas C
authors.initials: TC
authors.lastname: Cesario
authors.forename: Peter M
authors.initials: PM
authors.lastname: Rentzepis
mesh_terms: D000418:Albumins / Q000737:chemistry; D001419:Bacteria / Q000187:drug effects* / Q000528:radiation effects*; D003545:Cysteine / Q000737:chemistry; D006801:Humans; D006859:Hydrogen / Q000737:chemistry; D008027:Light; D008751:Methylene Blue / Q000737:chemistry*; D050296:Microbial Viability / Q000187:drug effects / Q000528:radiation effects; D009584:Nitrogen / Q000737:chemistry; D010100:Oxygen / Q000737:chemistry*; D010777:Photochemistry / Q000379:methods; D010949:Plasma / Q000737:chemistry / Q000382:microbiology*; D026082:Singlet Oxygen / Q000737:chemistry; D013053:Spectrophotometry; D013997:Time Factors
chemical_list: D000418:Albumins; D026082:Singlet Oxygen; D006859:Hydrogen; D003545:Cysteine; D009584:Nitrogen; D010100:Oxygen; D008751:Methylene Blue
keywords: ADPA; Leuco methylene blue; electrophilic attack; photoinactivation deficiency; transient spectroscopy