title: Green tea catechins quench the fluorescence of bacteria-conjugated Alexa fluor dyes.
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.
authors.affiliation: Department of Emergency Medicine, North Shore University Hospital, 350 Community Drive, Manhasset, NY 11030, USA. hwang@nshs.edu.
authors.forename: Lin
authors.initials: L
authors.lastname: Zhao
authors.forename: Wei
authors.initials: W
authors.lastname: Li
authors.forename: Shu
authors.initials: S
authors.lastname: Zhu
authors.forename: Sheena
authors.initials: S
authors.lastname: Tsai
authors.forename: Jianhua
authors.initials: J
authors.lastname: Li
authors.forename: Kevin J
authors.initials: KJ
authors.lastname: Tracey
authors.forename: Ping
authors.initials: P
authors.lastname: Wang
authors.forename: Saijun
authors.initials: S
authors.lastname: Fan
authors.forename: Andrew E
authors.initials: AE
authors.lastname: Sama
authors.forename: Haichao
authors.initials: H
authors.lastname: Wang
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000008:administration & dosage*; D058491:Bacterial Load; D002392:Catechin / Q000008:administration & dosage / Q000031:analogs & derivatives*; D002478:Cells, Cultured; D060085:Coinfection / Q000188:drug therapy* / Q000382:microbiology; D004926:Escherichia coli / Q000187:drug effects*; D004927:Escherichia coli Infections / Q000188:drug therapy* / Q000382:microbiology; D005453:Fluorescence; D006801:Humans; D006834:Hydrazines; D007274:Injections, Intraperitoneal; D051379:Mice; D008807:Mice, Inbred BALB C; D009930:Organic Chemicals; D013203:Staphylococcal Infections / Q000188:drug therapy* / Q000382:microbiology; D013211:Staphylococcus aureus / Q000187:drug effects*; D028242:Theaceae / Q000382:microbiology
chemical_list: C417561:Alexa 488 hydrazide; C417664:Alexa594; D000900:Anti-Bacterial Agents; D006834:Hydrazines; D009930:Organic Chemicals; D002392:Catechin; C057580:gallocatechol