 In the presence of light, phloxine B has a bactericidal effect on gram-positive strains, such as "Bacillus subtilis", "Bacillus cereus", and several methicillin-resistant "Staphylococcus aureus" (MRSA) strains.At a minimum inhibitory concentration of 25 μM, growth is reduced by 10-fold within 2.5 hours.At concentrations of 50 μM and 100 μM, growth is stopped completely and cell counts decrease by a factor of 104 to 105.