Phenolic-rich green tea extract increases the antibacterial activity of amoxicillin against Staphylococcus aureus by in vitro and ex vivo studies

Abstract

Context: Methicillin-resistant Staphylococcus aureus (MRSA) has been a significant challenge in health problems. Aims: To investigate synergistic properties of green tea extract that can potentially enhance the antibacterial activity of amoxicillin against methicillin-resistant Staphylococcus aureus (MRSA) in vitro and ex vivo. Methods: Green tea coarse powder was extracted by distilled water using high-pressure extraction. The total of phenolic and tannin contents was determined using spectrophotometry, and epigallocatechin gallate (EGCG) content was analyzed using Ultra-Fast Liquid Chromatography. Minimum Inhibitory Concentration (MIC) against MRSA was determined using a microdilution assay. Antibacterial assay of the combination of the extract and amoxicillin was performed using employing-checkerboard microdilution and agar diffusion assays. Results: The results exhibited that the green tea extract (GTE) contained total phenolic content of 545.6 ± 4.7 mg GAE/g extract; total tannin content of 356.6 ± 4.1 mg EGCG equivalent /g extract and EGCG of 221.1 ± 11.6 mg/g extract. The MICs combinatorial of GTE and ¼ MIC of amoxicillin was 75 µg/mL. Fractional Inhibitory Concentration Index value was 0.28, indicating that there was a synergy effect between amoxicillin and green tea extract. Essentially, the inhibitory zone diameter obtained by amoxicillin combined with ¼ MIC of GTE was two-fold than the zone produced by only amoxicillin. Although not significant, in ex vivo study, this combination was able to enhance the antibacterial activity of rat’s plasma against MRSA in vivo after the oral administration of GTE and amoxicillin. Conclusions: The results presented here serve as proof of concept for the enhancement of the antimicrobial activity of synthetic antibiotics when combined with a natural product.