Phloxine B

Phloxine B (CAS No.: 18472-87-2) is a synthetic xanthene-based red dye widely utilized as a biochemical reagent and color additive in pharmaceutical, cosmetic, and food applications, and it has gained relevance in biomedical research due to its functional interactions with microbial systems and ion channel regulation. Commonly known as D&C Red No. 28, it serves as a staining and visualization agent, including use in dental disclosing formulations and as an alternative differential stain for distinguishing Gram-negative and Gram-positive bacteria, reflecting its affinity for cellular components. Beyond its role as a colorant, Phloxine B exhibits biological activity, including inhibition of methicillin-resistant Staphylococcus aureus growth in vitro at defined concentrations and modulation of cystic fibrosis transmembrane conductance regulator chloride channels, affecting both wild-type and mutant forms at low micromolar levels. These properties position it as a useful probe for studying membrane transport, ion channel pharmacology, and antimicrobial responses. In research settings, it is applied in cell-based assays and microbiological studies to investigate cellular permeability, dye uptake, and antimicrobial susceptibility, with experimental concentrations varying according to assay design and biological context.