In vitro synergy of baicalein and gentamicin against vancomycin-resistant Enterococcus
Ping-Chin Chang, Hua-Yu Li, Hung-Jen Tang, Jien-Wei Liu, Jhi-Joung Wang, Yin-Ching Chuang
Departments of Internal Medicine and Family Medicine, Chi Mei Medical Center, Tainan; Department of Internal Medicine, Chang Gung Memorial Hospital, Kaohsiung; and Department of Medical Research, Chi Mei Medical Center, Tainan, Taiwan
Received: March 20, 2006 Revised: June 9, 2006 Accepted: June 20, 2006
Background and purpose:
Little is known about the possible synergism of baicalein, a bioactive flavone of Scutellariae radix (a Chinese herb), when used in conjunction with other antimicrobial agents against vancomycin-resistant Enterococcus (VRE). This in vitro study examined the possible synergism of the combination of baicalein and gentamicin against VRE.
Minimal inhibitory concentrations (MICs) of baicalein as well as gentamicin were determined against 39 clinical isolates of VRE by the agar dilution method. Synergistic activities were determined using the checkerboard method based on the fractional inhibitory concentration indices and also the time-kill method. Further time-kill studies were conducted with these two agents against one randomly chosen clinical isolate, VRE-096.
Minimal concentrations inhibiting 50% (MIC50) and 90% (MIC90) of isolates for baicalein and gentamicin were all >256 µg/mL. Synergism between baicalein and gentamicin was demonstrated against four clinical isolates of VRE (VRE-70, VRE-940, VRE-096 and VRE-721). When approximately 5 × 105 colony-forming units/mL of VRE-096 was incubated with both baicalein at a concentration of 32 µg/mL (1/8 × MIC) and gentamicin at a concentration of 128 µg/mL (1/2 × MIC), there was an inhibitory effect against VRE that persisted for 48 h. At 48 h, the combination of baicalein and gentamicin at these respective concentrations resulted in a reduction of growth by approximately 2 orders of magnitude compared to that for the starting inoculum and by 3 orders of magnitude compared to that for baicalein alone, the more active single agent.
This study demonstrated that baicalein and gentamicin can act synergistically in inhibiting VRE in vitro.
Baicalein; Drug synergism; Enterococcus; Microbial sensitivity tests; Vancomycin resistance
J Microbiol Immunol Infect 2007;40:56-61.