Molecular analysis of effects of Andrographis paniculata (Hempedu bumi) on oxidative stress enzymes and lipase in Staphylococcus aureus

A.paniculata leaves are known to have antimicrobial activities and is widely used in traditional medicine worldwide. This study investigated the anti-oxidative properties of methanolic leaves extract of A.paniculata (0.06 mg/ml, MIC) against S.aureus (ATCC 25923) (3.8 x 108 cfu/ml) by determining the ability of the extract to reduce toxicity of hydrogen peroxide (H2O2) against S.aureus. Effects of the extract on gene expressions were determined by RT-qPCR and corresponding activity assays of catalase (katA), superoxide dismutases (sodA and sodM), alkylhydroperoxide reductase C (ahpC) and lipase (geh) in S.aureus were also perfomed. For hydrogen peroxide (H₂O₂) sensitivity test, S.aureus cells (3.8 x 108cfu/ml) were challenged separately with 7.5 mM H2O2 only, 7.5 mM H₂O₂ and methanolic leaves extract of A.paniculata (0.06 mg/ml) and methanolic leaves extract of A.paniculata (0.06 mg/ml) only. Cells challenged with H₂O₂ only showed 0% survival in 30 minutes whereas 25% cells survived after treatment with the extract and H2O2. S.aureus cells that were treated with extract only had 43% survival in the same exposure period. Nitroblue tetrazolium (NBT) reduction assay was performed to determine intracellular and extracellular levels of O₂- after treatment with the extract. Extract –treated S.aureus cells had significantly lower intra- and extracellular O₂- levels with absorbance readings (A575nm) of 0.340 and 0.524 respectively compared to untreated cells which were 0.516 and 0.928 respectively (P<0.05).