Inhibition of penicillinase by epigallocatechin gallate resulting in restoration of antibacterial activity of penicillin against penicillinase-producing Staphylococcus aureus

Abstract

The combination of epigallocatechin gallate (EGCg, a main constituent of tea catechins) with penicillin showed synergism against 21 clinical isolates of penicillinase-producing Staphylococcus aureus. Besides binding directly to peptidoglycan, the inhibition of penicillinase activity by EGCg is responsible for the synergism. EGCg inhibited the penicillinase activity in a dose-dependent fashion, with a 50% inhibitory concentration of 10 microg/ml.

FIG. 1.

Protection of penicillin (A) and ampicillin (B) from penicillinase by EGCg. (A) Penicillin-susceptible S. aureus ATCC 25923 cells were inoculated in the cell-free supernatant containing about 0.015 U of penicillinase (PCase) per ml in the presence of twofold serial dilutions of penicillin and EGCg. (B) Ampicillin-susceptible E. coli ATCC 25922 cells were inoculated in MHB containing purified penicillinase at 0.001, 0.005, and 0.01 U/ml in the presence of twofold serial dilutions of ampicillin and EGCg. After incubation at 35°C for 24 h (S. aureus) and 18 h (E. coli), the MICs were determined.

FIG. 2.

Direct inhibition of penicillinase activity by EGCg. Purified penicillinase (10 U/ml) was incubated with EGCg in 100 μl of MHB at 35°C for 18 h prior to the addition of nitrocefin as its substrate. The optical density at 492 nm was then determined with a spectrophotometer.