Effect of Ca+ on the photobactericidal efficacy of methylene blue and toluidine blue against gram-negative bacteria and the dye affinity for lipopolysaccharides.
OBJECTIVE
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.


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.
Usacheva
Marina N
MN
Advanced Photodynamic Technologies, Inc., Minneapolis, Minnesota 55414, USA.
Teichert
Matthew C
MC
Sievert
Chet E
CE
Biel
Merrill A
MA
D002122:Calcium Chloride / Q000378:metabolism* / Q000494:pharmacology; D004396:Coloring Agents / Q000378:metabolism / Q000494:pharmacology*; D006090:Gram-Negative Bacteria / Q000187:drug effects*; D007834:Lasers; D008070:Lipopolysaccharides / Q000378:metabolism*; D008751:Methylene Blue / Q000378:metabolism / Q000494:pharmacology*; D013053:Spectrophotometry; D014048:Tolonium Chloride / Q000378:metabolism / Q000494:pharmacology*
D004396:Coloring Agents; D008070:Lipopolysaccharides; D014048:Tolonium Chloride; D002122:Calcium Chloride; D008751:Methylene Blue