Effects of Hopea Odorata roxb alcoholic extracts on mecA positive meticillin resistant Staphylococcus Aureus

Abstract

Methicillin resistant Staphylococcus aureus (MRSA) infection is a problem in hospitalized patients worldwide. Combination therapy is the alternative choice in the treatment of MRSA with the aim of decreasing the emergence of resistant strains and increasing the bacterial killing. MRSA often acquires multi-drug resistance and causes severe problems in clinical medicine. Therefore, the purpose of the present study is to determine the susceptibility of of H.odorata ROXB as compared to those of ampicillin and ampicillin/sulbactam against 30 MRSA isolates. The MIC₉₀ of the alcoholic extract of H.odorata ROXB, ampicillin and ampicillin/sulbactam were 125 μg/ml, 128 μg/ml and 32 μg/ml, respectively. Twenty-nine out of 30 isolates were beta-lactamase positive. All of the tested isolate were highly resistant to ampicillin (MIC range 8-128 μg/ml). The activity of the extract in combination with ampicillin and ampicillin/sulbactam were determined by Checkerboard method. Combination 1/2 MIC of the extract with ampicillin showed partial synergy against 22 isolates (73.33%) and additive against 13 isolates (26.67 %). While the combination 1/2 MIC of the extract with ampicillin/sulbactam showed partial synergy against 18 isolates (60 %) and additive against 12 isolates (40 %). In the Time kill study using MRSA 18 isolates (partial synergy in checkerboard method), combination of the extract 1/2 MIC with ampicillin showed bacteriostatic activity (90% killing) at 2, 4, 6 hr. The number of bacteria killed by the combination of extract 1/2 MIC plus 1/8 MIC ampicillin or 1/4 MIC ampicillin [BA₂₄ = 64.04, 43.77 log CFU/ml.h, respectively] were significantly higher than the number killed by ampicillin alone [BA₂₄ = 27.45, 18.43 log CFU/ml.h, respectively] (p<0.05). The combination of the extract 1/2 MIC with ampicillin/sulbactam showed bacteriostatic activity(90% killing) at 2, 4, 6 hr. The number of bacteria killed by the combination of extract 1/2 MIC plus 1/8 MIC ampicillin/sulbactam or 1/4 MIC ampicillin/sulbactam [BA₂₄ = 37.75, 45.76 log CFU/ml.h, respectively] were significantly higher than the number killed by ampicillin/sulbactam alone [BA₂₄ = 17.64, 25.75 log CFU/ml.h, respectively] (p<0.05). The results suggested that antibacterial activity of the combination between the herbal extract plus ampicillin or plus ampicillin/sulbactam were higher than the antibacterial activity of each drugs or herbal extract. It is concluded that the combination of extract plus ampicillin and ampicillin/sulbactam could be promising alternatives in the treatment of infections due to MRSA that were resistant to ampicillin and ampicillin/sulbactam.