Abstract
To investigate the effects of Andrographis paniculata (Burm.f.) Wall. Ex Nees (A.paniculata) on expressions and activities of catalase, superoxide dismutase and alkylhydroperoxide reductase C in Staphylococcus aureus (S.aureus) with respect to its survival invitro. Antioxidative property of methanolic leaves extract of A.paniculata (0.06mg/mL). Minimum inhibitory concentration (MIC) was determined by its ability to reduce hydrogen peroxide (H2O2) toxicity against S.aureus ATCC 25923 [(3.8×108)cfu/mL]. Effects of the extract on expressions of katA (encoding catalase), sodA and sodM [encoding superoxide dismutases (SODs)], and ahpC [encoding alkylhydroperoxide reductase C (AhpC)] in S.aureus were determined by RT-qPCR and corresponding enzyme activity assays were performed. Nitroblue tetrazolium reduction (NBT) assay was performed to determine effects of the extract on intracellular and extracellular levels of O2- in S.aureus. Cells challenged with 7.5mmol/L H2O2 showed 0% survival in 30min whereas 25% survived after treatment with the extract and H2O2. Cells that were treated with the extract alone had 43% survival in the same exposure period. Expressions of sodA and sodM genes in extract-treated cells were lowered 0.8-fold and 0.7-fold, respectively with decrease in total SOD activity of 26.8U compared to untreated cells, 32.4U (P<0.05). In contrast, extract-treated S.aureus cells showed 3.3-fold increase in katA expression with corresponding increase in catalase activity of 1.828U compared to untreated cells which was 1.248U, (P<0.05). More profoundly, ahpC expression was increased 61-fold in extract-treated cells, (P<0.05) with corresponding increase in AhpC activity of 0.018U compared to untreated cells, 0.012U, (P<0.05). Extract-treated cells had significantly lower intra- and extracellular O2- levels with absorbance readings (A575nm) of 0.340 and 0.524 compared to untreated cells which were 0.516 and 0.928 (P<0.05), respectively. Taken together these results suggest that the low MIC of A.paniculata methanolic leaves extract (0.06mg/mL) reduce H2O2 toxicity and more importantly, was in itself effectively inhibitory against S.aureus. Further, our observations suggest that a probable mode of its inhibitory mechanism against S.aureus is by reducing total SOD activity through downregulation of sodA and sodM expressions.
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