Composition, Anti-MRSA Activity and Toxicity of Essential Oils from Cymbopogon Species

Many of the essential oils obtained from medicinal plants possess proven antimicrobial activity and are suitable for medicinal purposes and applications in the food industry. The aim of the present work was the chemical analysis of 19 essential oils (EOs) from seven different Cymbopogon species (C. nardus, C. citratus, C winterianus, C. flexuosus, C. schoenanthus, C. martinii, C. giganteus). Five different chemotypes were established by GC/MS and TLC assay. The EOs, as well as some reference compounds, i.e., citronellol, geraniol and citral (neral + geranial), were also tested for their antimicrobial and antibiofilm activity against methicillin-resistant Staphylococcus aureus (MRSA) by the microdilution method and direct bioautography. The toxicity of EOs was evaluated by Danio rerio ‘Zebrafish’ model assay. All examined EOs showed moderate to high activity against MRSA, with the highest activity noted for C. flexuosus—lemongrass essential oil, both in microdilution and direct autobiography method. Significant difference in the toxicity of the examined EOs was also detected.

In Vitro Qualitative Phytochemical Screening, Tlc-Bioautography and Spot Screening of Bistorta Amplexicaulis (D.DON) Greene Extracts

The biological activities of Bistorta amplexicaulis (D.Don) Greene rhizome and leaves extracts were evaluated. In vitro antibacterial activity, direct bioautography, and spot screening of TLC developed bands were investigated against seven bacterial pathogens. Screening of phytochemical constituents was also done through both qualitative and thin layer chromatographic methods. DMSO extracts of rhizome indicated high sensitivity (12.33 ± 1.52 and 11.33 ± 0.57 mm) against Escherichia coli. Whereas methanolic and acetonic extracts of rhizome indicated significant inhibition (11.66 ± 1.15 and 11.33 ± 0.57 mm) of S. marcesscens. All leaf extracts revealed low sensitivity against E. coli. TLC-bioautography and spot screening methods showed the significant use of B. amplexicaulis as an antibacterial agent. Antioxidant activity indicated that acetone and DMSO extracts of rhizome and methanolic leaf extract have maximum scavenging potential. Among the screened phytochemicals, terpenoids, phenols, and quinones were detected in all extracts indicating the potential use of B. amplexicaulis as both antibacterial and antioxidant agents. Bangladesh J. Bot. 50(3): 613-622, 2021 (September)

Diffusible Compounds Produced by Hanseniaspora osmophila and Gluconobacter cerinus Help to Control the Causal Agents of Gray Rot and Summer Bunch Rot of Table Grapes

Gray and summer bunch rot are important diseases of table grapes due to the high economic and environmental cost of their control with synthetic fungicides. The ability to produce antifungal compounds against the causal agents Botrytis, Aspergillus, Penicillium, and Rhizopus of two microorganisms isolated from table grapes and identified as Hanseniaspora osmophila and Gluconobacter cerinus was evaluated. In dual cultures, both biocontrol agents (together and separately) inhibited in vitro mycelial growth of these pathogens. To identify the compounds responsible for the inhibitory effect, extractions were carried out with organic solvents from biocontrol agents separately. Through dual cultures with pathogens and pure extracts, only the hexane extract from H. osmophila showed an inhibitory effect against Botrytis cinerea. To further identify these compounds, the direct bioautography technique was used. This technique made it possible to determine the band displaying antifungal activity at Rf = 0.05–0.2. The compounds present in this band were identified by GC-MS and compared to the NIST library. The most abundant compounds, not previously reported, corresponded to alkanes, ketones, alcohols, and terpenoids. H. osmophila and G. cerinus have the potential to control the causal agents of gray and summer bunch rot of table grapes.

Direct bioautography for the screening of selected tropical wood extracts against basidiomycetes

To understand the reasons for the high durability of tropical wood species, the chemistry of the extractives needs to be elucidated. As these extractives consist of a great variety of components differing in quantity and composition, the analysis is often time-consuming. To focus on the key bioactive substances, bioassay-guided fractionation is helpful, but the established bioassay methods cannot be readily adapted to basidiomycete fungi that are commonly used for the respective durability tests, because they do not sporulate easily in laboratory settings. The research therefore aims at developing a direct bioautography using homogenized hyphae from basidiomycetes, to overcome this restriction. Extracts from four tropical wood species were analyzed regarding their potential bioactivity on two selected basidiomycete fungi. To this end, the chemically complex mixtures and extract constituents were resolved by a two-dimensional planar chromatography and the metabolites were located by characteristic zones of fungal growth inhibition, which was accentuated by a color reaction. The bioactive fractions were analyzed by gas chromatography/mass spectrometry (GC/MS). Potentially responsible compounds could be identified, such as the alkaloid bicuculline from Mezilaurus itauba, which has not been described in this species yet. The presented bioassay method can be used as a rapid screening method for bioactive components from wood.

TLC Bioautography on Screening of Bioactive Natural Products: An Update Review

Background: TLC bioautography is a hyphenated technique combining planar chromatographic separation and in situ biological activity detection. This coupled method has been receiving much attention in screening bio-active natural products because of its properties of being simple, rapid, inexpensive, and effective. Methods: The recent progress in the development of method of TLC bioautography for detecting antimicrobial and enzyme inhibitory activities dating between 2012 and early 2018 has been reviewed. The applications of this method in biological screening of natural products were also presented. Results: Some anaerobic and microaerophilic bacteria and a causative bacterium of tuberculosis have been adopted to TLC direct bioautography. Seven types of enzymes including acetylcholinesterase, glucosidase, lipase, xanthine oxidase, tyrosinase, monoamine oxidase, and dipeptidyl peptidase IV have so far been adopted on TLC bioautography. Its new application in screening antiurolithiatic agents was included. Conclusion: The standard experimental procedures are required for TLC antioxidant and antimicrobial assays. Some new enzymes should be attempted and adopted on TLC bioautography. The existing TLC methods for enzyme inhibition need more application studies to assess their screening capacity in the discovery of active compounds. The GC-MS or LC-MS approaches have gradually been coupled to TLC bioautography for fast structural characterization of active compounds.

Isolation of Flavonoids from Anaphalis Busua and their Antibacterial Activity

Anaphalis busua (Buch-Ham ex D. Don) is traditionally used to treat cuts and wounds. In the agar dilution method, the hexane extract of the aerial part of A. busua exhibited potent antibacterial activity with a minimal inhibitory concentration of 25 μg/ml against Bacillus subtilis and 500 μg/ml against Staphylococcus aureus. For the isolation of antibacterial compounds, the hexane extract was fractionated by silica gel and Sephadex LH 20 column chromatography. The direct bioautography method was used to determine the antibacterial activity of the fractions. The active fractions were finally purified by semi-preparative HPLC on C18 Phenomenex column under gradient condition. Four flavones derivatives of 3,5-dihydroxy-6,7,8-trimethoxyflavone (1), 3,5,7-trihydroxy-6-methoxyflavone (alnusin) (2), 3,5,7-trihydroxy-8-methoxyflavone (3) and pinocembrin (4) were isolated, and their structures were established by 1H, 13C, DEPT-135, and ESI-MS spectroscopy. These compounds were isolated for the first time from A. busua. The fatty acid profile of the hexane extract was analyzed by gas chromatography-mass spectrometry (GC-MS) by silylation with N-methyl-N-trimethylsilyl-trifluoro-acetamide. Pinocembrin showed antibacterial activity with the minimum inhibitory concentration of 60 μg/mL against Bacillus subtilis and 420 μg/mL against Staphylococcus aureus.