Title:Green Tea Catechins Quench the Fluorescence of Bacteria-Conjugated Alexa Fluor Dyes
Volume: 12
Issue: 5
Author(s): Lin Zhao, Wei Li, Shu Zhu, Sheena Tsai, Jianhua Li, Kevin J. Tracey, Ping Wang, Saijun Fan, Andrew E. Sama and Haichao Wang
Affiliation:
Keywords:
Alexa Fluor 488, Alexa Fluor 594, antimicrobial, EGCG, fluorescence intensity, macrophage, sepsis, tissue
bacterial load.
Abstract: Accumulating evidence suggests that Green tea polyphenolic catechins, especially the (-)-epigallocatechin
gallate (EGCG), can be cross-linked to many proteins, and confer a wide range of anti-bacterial activities possibly by
damaging microbial cytoplasmic lipids and proteins. At the doses that conferred protection against lethal polymicrobial
infection (induced by cecal ligation and puncture), EGCG significantly reduced bacterial loads particularly in the liver and
lung. To elucidate its bactericidal mechanisms, we determined whether EGCG affected the fluorescence intensities of
bacteria-conjugated Alexa Fluor 488 or 594 dyes. When mixed with unconjugated Alexa Fluor 488 or 594 dyes, EGCG or
analogs did not affect the fluorescence intensity of these dyes. In a sharp contrast, EGCG and some analogs (e.g.,
Catechin Gallate, CG), markedly reduced the fluorescence intensity of Gram-positive Staphylococcus aureus-conjugated
Alexa 594 and Gram-negative Escherichia coli-conjugated Alexa 488. Interestingly, co-treatment with ethanol impaired
the EGCG-mediated fluorescence quenching of the G+ S. aureus, but not of the G- E. coli-conjugated Alexa Flour dyes. In
light of the notion that Alexa Fluor dyes can be quenched by aromatic amino acids, it is plausible that EGCG exerts antimicrobial
activities possibly by altering microbial protein conformations and functions. This possibility can now be
explored by screening other fluorescence-quenching agents for possible antimicrobial activities.
