Antibacterial effect of rose bengal against colistin-resistant gram-negative bacteria.

Increasing drug resistance in Gram-negative bacteria presents significant health problems worldwide. Despite notable advances in the development of a new generation of β-lactams, aminoglycosides, and fluoroquinolones, it remains challenging to treat multi-drug resistant Gram-negative bacterial infections. Colistin (polymyxin E) is one of the most efficacious antibiotics for the treatment of multiple drug-resistant Gram-negative bacteria and has been used clinically as a last-resort option. However, the rapid spread of the transferable gene, mcr-1 which confers colistin resistance by encoding a phosphoethanolamine transferase that modifies lipid A of the bacterial membrane, threatens the efficacy of colistin for the treatment of drug-resistant bacterial infections. Colistin-resistant strains of Pseudomonas aeruginosa, Acinetobacter baumannii, and Klebsiella pneumoniae often reduce their susceptibility to other anti-Gram-negative bacterial agents. Thus, drugs effective against colistin-resistant strains or methods to prevent the acquisition of colistin-resistance during treatment are urgently needed. To perform cell-based screenings of the collected small molecules, we have generated colistin-resistant strains of E. coli, A. baumannii, K. pneumoniae, P. aeruginosa, and S. enterica Typhimurium. In-house MIC assay screenings, we have identified that rose bengal (4,5,6,7-tetrachloro-2',4',5',7'-tetraiodofluorescein) is the only molecule that displays unique bactericidal activity against these strains at low concentrations under illumination conditions. This article reports the antibacterial activity of a pharmaceutical-grade rose bengal against colistin-resistant Gram-negative bacteria.