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Effect of Ca + on the photobactericidal efficacy of methylene blue and toluidine blue against gram‐negative bacteria and the dye affinity for lipopolysaccharides
Author(s) -
Usacheva Mari.,
Teichert Matthew C.,
Sievert Chet E.,
Biel Merrill A.
Publication year - 2006
Publication title -
lasers in surgery and medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.888
H-Index - 112
eISSN - 1096-9101
pISSN - 0196-8092
DOI - 10.1002/lsm.20400
Subject(s) - methylene blue , metachromasia , chemistry , toluidine , bacteria , photobleaching , membrane , gram negative bacteria , microbiology and biotechnology , biochemistry , escherichia coli , fluorescence , organic chemistry , biology , staining , gene , physics , photocatalysis , quantum mechanics , genetics , catalysis
Background and Objectives Methylene blue (MB) and toluidine blue (TB) form metachromatic complexes with lipopolysaccharides (LPS). The greater photobactericidal efficacy of TB may be explained by its affinity for LPS. This study aims to elucidate the difference in photobactericidal efficacies between the dyes using Ca 2+ as a competitor for dye‐binding sites on the bacterial outer membrane. Study Design/Materials and Methods Fixed dye concentration solutions with gram‐negative bacteria and increasing concentrations of CaCl 2 were exposed to red laser light. Bacterial survival and spectrophotometry were used to describe the effect of Ca 2+ on dye interaction with bacteria and LPS. Results MB‐mediated photokilling was inhibited more significantly than that of TB. CaCl 2 inhibited dye photobleaching and suppressed the metachromatic reaction between the dyes and LPS, in particular TB. Conclusions CaCl 2 inhibits bacterial photokilling by binding with LPS, as well as other anionic polymers including outer membrane proteins. LPS is chiefly involved in TB‐mediated photokilling, whereas outer membrane proteins probably are more involved in MB‐mediated photokilling. Lasers Surg. Med. 38:946–954, 2006. © 2006 Wiley‐Liss, Inc.