The antioxidant and antimicrobial activity of ethanolic extract in roots, stems, and leaves of three commercial Cymbopogon species

BACKGROUND

Cymbopogon is a member of the family Poaceae and has been explored for its phytochemicals and bioactivities. Although the antimicrobial activities of Cymbopogon spp. extracts have been extensively studied, comprehensive analyses are required to identify promising compounds for the treatment of antimicrobial resistance. Therefore, this study investigated the antioxidant and antimicrobial properties of Cymbopogon spp. ethanolic extracts in every single organ.

METHODS

Ethanolic extracts were obtained from three Indonesian commercial species of Cymbopogon spp., namely Cymbopogon citratus (L.) Rendle, Cymbopogon nardus (DC.) Spatf., and Cymbopogon winterianus Jowitt. The leaf, stem, and root extracts were evaluated via metabolite profiling using gas chromatography-mass spectrometry (GC-MS). In silico and in vitro analyses were used to evaluate the antioxidant and antimicrobial properties of the Cymbopogon spp. ethanolic extracts. In addition, bioactivity was measured using cytotoxicity assays. Antioxidant assays were performed using 1,1-diphenyl-2-picrylhydrazyl (DPPH) and 2,2-azino-bis [3-ethylbenzothiazoline-6-sulfonic acid (ABTS) to determine toxicity to Huh7it-1 cells using a tetrazolium bromide (MTT) assay. Finally, the antimicrobial activity of these extracts was evaluated against Candida albicans, Bacillus subtilis, Staphylococcus aureus, and Escherichia coli using a well diffusion assay.

RESULTS

GC-MS analysis revealed 53 metabolites. Of these, 2,5-bis(1,1-dimethylethyl)- phenol (27.87%), alpha-cadinol (26.76%), and 1,2-dimethoxy-4-(1-propenyl)-benzene (20.56%) were the predominant compounds. C. winterianus and C. nardus leaves exhibited the highest antioxidant activity against DPPH and ABTS, respectively. Contrastingly, the MTT assay showed low cytotoxicity. C. nardus leaf extract exhibited the highest antimicrobial activity against E. coli and S. aureus, whereas C. winterianus stem extract showed the highest activity against B. substilis. Furthermore, computational pathway analysis predicted that antimicrobial activity mechanisms were related to antioxidant activity.

CONCLUSIONS

These findings demonstrate that the leaves had strong antioxidant activity, whereas both the leaves and stems showed great antimicrobial activity. Furthermore, all Cymbopogon spp. ethanolic extracts showed low toxicity. These findings provide a foundation for future studies that assess the clinical safety of Cymbopogon spp. as novel drug candidates.

The Influence of Carrier Oils on the Antimicrobial Activity and Cytotoxicity of Essential Oils

The topical use of essential oils requires dilution into a carrier oil; however, scientific evidence regarding the antimicrobial efficacy and cytotoxicity when a carrier oil is combined with an essential oil is lacking. This study sets out to determine the antimicrobial activity and cytotoxicity of 23 essential oils combined with six known carrier oils. Gas chromatography-mass spectrometry/flame ionization detector (GC-MS/FID) was used to characterize the methyl esters of the carrier oils. The antimicrobial activity of the carrier oils alone and in combination with the essential oils was investigated using the broth microdilution assay against 11 skin pathogens and the cytotoxicity was determined using the brine shrimp lethality assay. The interactive profiles of the combinations for both antimicrobial activity and the cytotoxicity were analysed and calculated using the fractional inhibitory concentration index (ΣFIC). The carrier oils demonstrated no antimicrobial antagonism when combined with the essential oils and the overall cytotoxicity of the majority of the combinations was decreased. The carrier oils that could be identified as enhancing the antimicrobial activity and decreasing the cytotoxicity were Aloe vera Mill. and Simmondsia chinensis C.K.Schneid (Jojoba oil), with an overall reduction in essential oil cytotoxicity of 87.5% at 24 hrs and 85% at 48 hrs by A. vera. Five of the essential oils (when diluted in A. vera and S. chinensis carrier oils) demonstrated enhanced antimicrobial activity against pathogens such as Brevibacterium epidermidis, B. linens, and P. aeruginosa with MIC values ranging from 0.09 to 0.50 mg/mL (and ΣFIC 0.14-0.39). The study could conclude that the carrier oils are complementary to essential oil formulations, mostly reducing cytotoxicity and in some cases enhancing the antimicrobial activity.