Synergism and the mechanism of action of the combination of α-mangostin isolated from Garcinia mangostana L. and oxacillin against an oxacillin-resistant Staphylococcus saprophyticus

Abstract

BackgroundGlobally, staphylococci have developed resistance to many antibiotics. New approaches to chemotherapy are needed and one such approach could be to use plant derived actives with conventional antibiotics in a synergestic way. The purpose of this study was to isolate α-mangostin from the mangosteen (Garcinia mangostana L.; GML) and investigate antibacterial activity and mechanisms of action when used singly and when combined with oxacillin against oxacillin-resistant Staphylococcus saprophyticus (ORSS) strains. The isolated α-mangostin was confirmed by HPLC chromatogram and NMR spectroscopy. The minimum inhibitory concentration (MIC), checkerboard and killing curve were determined. The modes of action of these compounds were also investigated by enzyme assay, transmission electron microscopy (TEM), confocal microscopic images, and cytoplasmic membrane (CM) permeabilization studies.ResultsThe MICs of isolated α-mangostin and oxacillin against these strains were 8 and 128 μg/ml, respectively. Checkerboard assays showed the synergistic activity of isolated α-mangostin (2 μg/ml) plus oxacillin (16 μg/ml) at a fractional inhibitory concentration index (FICI) of 0.37. The kill curve assay confirmed that the viability of oxacillin-resistant Staphylococcus saprophyticus DMST 27055 (ORSS-27055) was dramatically reduced after exposure to isolated α-mangostin (2 μg/ml) plus oxacillin (16 μg/ml). Enzyme assays demonstrated that isolated α-mangostin had an inhibitory activity against β-lactamase in a dose-dependent manner. TEM results clearly showed that these ORSS-27055 cells treated with this combination caused peptidoglycan and cytoplasmic membrane damage, irregular cell shapes and average cell areas were significantly larger than the control. Clearly, confocal microscopic images confirmed that this combination caused considerable peptidoglycan damage and DNA leakage. In addition, the CM permeability of ORSS-27055 was also increased by this combination of actives.ConclusionsThese findings provide evidence that isolated α-mangostin alone has not only some activity but also shows the synergistic activity with oxacillin against ORSS-27055. The chromone and isoprenyl structures could play a significant role in its action. This synergistic activity may involve three mechanisms of action. Firstly, potential effects of cytoplasmic membrane disruption and increases permeability. Secondly, inhibit β-lactamase activity. Finally, also damage to the peptidoglycan structure. We proposes the potential to develop a novel adjunct phytopharmaceutical to oxacillin for the treatment of ORSS. Future studies require clinical trials to establish if the synergy reported can be translated to animals and humans.

Synergy and mechanism of action of α-mangostin and ceftazidime against ceftazidime-resistant Acinetobacter baumannii

“…These findings seem to correspond with previous findings showing that the combination of isolated α ‐mangostin and oxacillin exhibited peptidoglycan and cytoplasmic membrane damage, irregular cell shapes of oxacillin‐resistant Staphylococcus saprophyticus and average cell areas significantly larger than those of the controls (Phitaktim et al . ).…”

“…that the isolated α ‐mangostin inhibited β ‐lactamase in a dose‐dependent manner (Phitaktim et al . ). This result may enhance the rapid killing by a membrane‐targeting antimicrobial, and that β ‐lactamase inhibition could be a secondary effect of the membrane disruption (Koh et al .…”

“…; Phitaktim et al . ) and would suggest that the AMT could potentially be a useful adjuvant to CTZ for the treatment of CRAB.…”

“…was used to assess the activity of AMT in combination with CTZ or CTX (Phitaktim et al . ). The FIC index was calculated using the following formula:…”

“…; Phitaktim et al . ), there is currently little to no information on the potential synergy when targeting cephalosporin‐resistant A. baumannii strains. This study sought to evaluate the in vitro antimicrobial effect of α ‐mangostin alone and combined with ceftazidime against CRAB strains and to investigate any potential synergistic mechanism.…”