In Vitro Antibacterial Activities of Phloxine B and Other Halogenated Fluoresceins against Methicillin-Resistant Staphylococcus aureus

Fluorescein dyes in which the benzoic acid moiety has been tetrachlorinated (50 to 100 μg/ml) inhibit in vitro Staphylococcus aureus growth (MIC, 25 μg/ml). Specifically, under standard room illumination, phloxine B at a concentration of 100 μg/ml killed 99% of the cultures (mid-log phase). It also reduced S. aureus CFU by 10(4). Structure-activity analysis revealed that the activity against S. aureus increases with the increase in the number of the substituting halogens in the hydroxyxanthene moiety.