Vancomycin resistance reversal in enterococci by flavonoids

The development of clinical vancomycin‐resistant strains of enterococci (VRE) is a major cause for concern. Here we show that a combination of galangin or 3,7‐dihydroxyflavone with vancomycin may be used to sensitize resistant strains of Enterococcus faecalis and Enterococcus faecium to the level of vancomycin‐sensitive strains. Minimum inhibitory concentrations (MICs) and viable counts were determined in Iso‐sensitest broth using a microtitre method. MICs of vancomycin against 67% of resistant clinical isolates and a type strain of enterococci were lowered from > 250 μg mL−1 to < 4 μg mL−1 in the presence of galangin (12.5 μg mL−1) or 3,7‐dihydroxyflavone (6.25 μg mL−1). Viable counts for type culture E. faecalis ATCC 51299 showed the flavonoids alone significantly lowered numbers of colony forming units (CFUs). CFUs were maintained at low levels (< 103 CFU mL−1) for 24 h by vancomycin/flavone combinations. This combinational action in reversing vancomycin resistance of enterococci highlights novel drug targets and has importance in the design of new therapeutic regimes against resistant pathogens.