Interaction of the photobactericides methylene blue and toluidine blue with a fluorophore in Pseudomonas aeruginosa cells

• Published in: Lasers in surgery and medicine Vol. 40; no. 1; pp. 55 - 61
• Main Authors: Usacheva, M.N., Teichert, M.C., Usachev, Y.M., Sievert, C.E., Biel, M.A.
• Format: Journal Article
• Language: English
• Published: Hoboken Wiley Subscription Services, Inc., A Wiley Company 01-01-2008
• Subjects: Coloring Agents - metabolism; Coloring Agents - pharmacology; fluorescence quenching; Lasers; methylene blue; Methylene Blue - metabolism; Methylene Blue - pharmacology; Microscopy, Confocal; Oligopeptides; photobactericidal efficacy; Pseudomonas aeruginosa; Pseudomonas aeruginosa - drug effects; Pseudomonas aeruginosa - radiation effects; pyoverdin; Siderophores - radiation effects; Tolonium Chloride - metabolism; Tolonium Chloride - pharmacology; toluidine blue
• ISSN: 0196-8092; 1096-9101
• DOI: 10.1002/lsm.20593

Background and Objectives
The difference in photobactericidal efficacy between methylene blue (MB) and toluidine blue (TB) may be explained by their involvement with proteins, lipopolysaccharides (LPS), and siderophores and siderophore‐receptor protein complexes on the bacterial outer membrane. This study aims to determine if this is the case by using the fluorescence given off by a pseudomonal siderophore named pyoverdin.
Study Design/Materials and Methods
Confocal laser scanning microscopy was used to observe the fluorescence of Pseudomonas aeruginosa cells excited at 488 nm in the presence of increasing dye concentrations.
Results
Cellular fluorescence at 522 nm progressively decreased with increasing dye concentrations. The Stern–Volmer constants for cellular fluorescence quenching with the dyes were compared to the association constants for dyes complexed with LPS. The quenching of cellular fluorescence was associated with the formation of a ground‐state complex between the dyes and pyoverdin–FpvA protein system. MB readily complexed with this system, whereas TB complexed more strongly with LPS.
Conclusion
The different affinities of the dyes for both pyoverdin–protein and LPS will affect the contributions of the dyes' interactions with these biopolymers to the overall bacterial photodamage. Lesers Surg. Med. 40:55–61, 2008. © 2008 Wiley‐Liss, Inc.