In vitro synergy of baicalein and gentamicin against vancomycin-resistant Enterococcus.
OBJECTIVE
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.


METHODS
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.


RESULTS
Minimal concentrations inhibiting 50% (MIC(50)) and 90% (MIC(90)) of isolates for baicalein and gentamicin were all >256 microg/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 x 10(5) colony-forming units/mL of VRE-096 was incubated with both baicalein at a concentration of 32 microg/mL (1/8 x MIC) and gentamicin at a concentration of 128 microg/mL (1/2 x 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.


CONCLUSIONS
This study demonstrated that baicalein and gentamicin can act synergistically in inhibiting VRE in vitro.
Chang
Ping Chin
PC
Department of Internal Medicine, Chi Mei Medical Center, Tainan, Taiwan.
Li
Hua Yu
HY
Tang
Hung Jen
HJ
Liu
Jien Wei
JW
Wang
Jhi Joung
JJ
Chuang
Yin Ching
YC
D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D024881:Drug Resistance, Bacterial; D004357:Drug Synergism; D016983:Enterococcus / Q000187:drug effects*; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D044950:Flavanones / Q000494:pharmacology*; D005839:Gentamicins / Q000494:pharmacology*; D016908:Gram-Positive Bacterial Infections / Q000382:microbiology; D006801:Humans; D008826:Microbial Sensitivity Tests; D014640:Vancomycin / Q000494:pharmacology*
D000900:Anti-Bacterial Agents; D004791:Enzyme Inhibitors; D044950:Flavanones; D005839:Gentamicins; C006680:baicalein; D014640:Vancomycin