Evaluation of the Combined Effects of Stilbenoid from Shorea gibbosa and Vancomycin against Methicillin-Resistant Staphylococcus aureus (MRSA)

Chan Kin Luoi,Jalifah Latip,Dayang Fredalina Basri,Abdul Muin Azmi

doi:10.3390/ph5091032

Abstract

The aim of this study is to determine the combined effects of stilbenoids from Shorea gibbosa and vancomycin against methicillin-resistant Staphylococcus aureus (MRSA). A total of nine pure compounds, five stilbenoid dimers ε-viniferin, ampelopsin A, balanocarpol, laevifonol and diptoindonesin G and four stilbenoid trimers α-viniferin, johorenol A, ampelopsin E and vaticanol G were evaluated for their antibacterial activities against ATCC 33591 and a HUKM clinical isolate. Minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) for each active compound were determined using the serial microdilution and plate-streak techniques. The combined effect of stilbenoids with vancomycin against MRSA was evaluated using the checkerboard assay to determine their fractional inhibitory concentration (FIC) index values. The MIC value of α-viniferin on both MRSA strains was 100 μg/mL, whereas those of johorenol A on ATCC 33591 and HUKM strain were 100 μg/mL and 200 μg/mL, respectively. The MIC values of ampelopsin E and vaticanol G were higher than 400 μg/mL. Out of the five stilbenoid dimers, only ε-viniferin was capable of inhibiting the growth of both MRSA strains at MIC 400 μg/mL. The MBC value of ε-viniferin, α-viniferin and johorenol A showed bacteriostatic action against MRSA. The FIC index value of ε-viniferin and α-viniferin in combination with vancomycin showed an additive effect (0.5 < FIC ≤ 2.0) against both MRSA strains. Johorenol A-vancomycin combination was also additive against HUKM strain, but it showed synergistic interaction with vancomycin against ATCC 33591 (FIC < 0.5). Stilbenoid compounds from Shorea gibbosa have anti-MRSA activity and huge potential as an alternative phytotherapy in combating MRSA infections.

Highlights

Staphylococcus aureus is a type of normal microflora, which can be found on the skin and nose of a healthy person
Out of the five dimer compounds studied, only ε-viniferin was capable of inhibiting both methicillin-resistant Staphylococcus aureus (MRSA) strains at Minimum inhibitory concentration (MIC) value 400 μg/mL whereas ampelopsin A, balanocarpol, laevifonol and diptoindonesin G were not capable of inhibiting the growth of MRSA at concentrations ranging from 400 μg/mL–0.78 μg/mL
This study revealed that the stilbenoind ε-viniferin, -viniferin and johorenol A are bacteriostatic towards the growth of MRSA

Summary

Introduction

Staphylococcus aureus is a type of normal microflora, which can be found on the skin and nose of a healthy person. This bacterium will become an opportunistic pathogen if it enters the body through a minor trauma or surgical wound in persons with compromised immune systems to cause skin and soft-tissue infections such as furunculosis and folliculitis [1]. S. aureus has become the major burn pathogen [2], as the primary isolate recovered in 75% of burn patients dying of septicaernia. In patients with diabetes mellitus, S. aureus may be seen with increased frequency because of alterations in the mechanical barrier of the skin and vascular abnormalities common in people with diabetes [6]

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