Restoration of antibacterial activity of β-lactams by epigallocatechin gallate against β-lactamase-producing species depending on location of β-lactamase

The combined effects of (-)-epigallocatechin gallate (EGCg) and beta-lactams were investigated against various beta-lactamase-producing clinical isolates, including 21 Staphylococcus aureus, 6 Escherichia coli, 3 Klebsiella pneumoniae and 8 Serratia marcescens strains. Penicillin in combination with EGCg at 12.5 mug mL(-1) showed the most potent synergy against 100% penicillinase-producing S. aureus. However, cefotaxime or imipenem in combination with higher concentration of EGCg (100 mug mL(-1)) only showed slight synergy against 2 of 17 Gram-negative rods. Similar to the effect on the penicillinase from S. aureus, however, EGCg also directly inhibited the extracted beta-lactamases from the Gram-negative rods, thereby protecting beta-lactams from inactivation. The different effects of the combinations on different beta-lactamase-producing species were confirmed to be related to the cellular locations of beta-lactamases. In contrast to a 32.7% extracellular fraction of total beta-lactamase activity in a penicillinase-producing S. aureus, the fractions were 0.6%, 0.6% and 1.2% in a TEM-derived extended-spectrum beta-lactamase-producing E. coli, an inhibitor-resistant beta-lactamase-producing K. pneumoniae and an IMP-producing S. marcescens, respectively. In conclusion, the combination of penicillin with EGCg showed potent synergy against penicillinase-producing S. aureus in-vitro. The combinations of beta-lactams and EGCg against beta-lactamase-producing Gram-negative rods do indicate a limitation owing to the cellular location of beta-lactamases.