Expanding the bactericidal action of the food color additive phloxine B to gram-negative bacteria.

Phloxine B (D&C red no. 28) is a color additive for food, drugs, and cosmetics. It has been previously shown to have anti-Staphylococcus aureus activities. In this work, the effect of Phloxine B on various gram-negative bacteria and other gram-positive bacteria including Bacillus cereus, Bacillus thuringiensis, Bacillus mycoides, Bacillus subtilis, Bacillus aureus, Salmonella, Escherichia coli and Shigella was studied, along with the mechanism of anti-microbial activity. In the presence of fluorescent light, the viable count for gram-positive bacteria, (Bacillus spp. and S. aureus) decreased in a dose and time dependent manner when incubated with Phloxine B. The viability of gram-positive bacteria was reduced by 99.99% in 40 min, while there was no effect on gram-negative bacteria (Salmonella choleraesuis, E. coli and Shigella flexneri). However, the use of ethylenediaminetetraacetic acid (EDTA) expands the spectrum of activity for Phloxine B to include gram-negative bacteria. EDTA increased membrane-permeability by releasing lipopolysaccharide. Overall, in an Agar diffusion test the light-dependent bactericidal activity of 1 microg of Phloxine B had a potency of 0.64 units of chloramphenicol and 0.5 units of tetracycline when tested on B. cereus, and had a potency of 0.7 units of chloramphenicol and 0.2 units of tetracycline when tested on S. aureus. The data suggest that the dye may have some potential anti-microbial applications.