Medicinal plants have a long tradition of use in folk and conventional medicine. In recent years numerous studies confirm various bioactivities of natural products, among them antibacterial activity. Natural antibacterial agents such are essential oils and isolated compounds now represent a notable source for pharmaceutical and food industry and are widely used in cosmetology. They meet standards of 'green consumerism' together with excellent antibacterial activity. Aromatic plants such is Thymus vulgaris L. are the major sources of essential oils. Thyme essential oil, as well as dominant compounds thymol and carvacrol are generally recognised as safe and have been registered by European Commission for use as flavouring agents in foodstuffs. However, essential oil is present in very low amount (0,8-2,6%) in thyme leaves. Thus, the majority of plant material remains unused after the isolation. Nowadays, the biological potential of various plant waste materials are in focus of numerous studies. These investigations also include the antimicrobial activity considering the fact that waste material extracts represent the valuable source of different phenolic compounds. Regarding all this, the aim of the present study was to determine antibacterial potential of chemically characterised extracts obtained from waste material remaining after the preparation of drug (stems) and isolation of thyme essential oil (deodorised leaves, postdistillation decoction) on selected bacterial strains. Also, in order to determine safety of waste extracts their cytotoxicity was investigated. All extracts were prepared with maceration using 45% or 75% ethanol (EtOH) for 24 h at room temperature (1:10 w/v). Total phenolic compounds and flavonoids were determined spectrophotometrically. Extracts were chemically characterized by HPLC/DAD analysis. Antibacerial testing was done with broth dilution method against several bacterial strains (Staphylococcus aureus, Bacillus cereus, Salmonella infantis, Escherichia coli and Campylobacter jejuni). Cytotoxicity and cytoprotection studies were performed by XTT assay. Result of HPLC analysis showed that investigated extracts, especially those obtained from deodorised leaves represent a valuable source of rosmarinic acid and luteolin 7-O-glucuronide. Antibacterial testing indicated that all waste material extracts, except the extract T2, possess similar or even stronger bacteriostatic activity than T1. No cytotoxicity nor cytoprotection were determined. In conclusion, results of this study confirmed antibacterial potential investigated thyme extracts. High concentrations of rosmarinic acid and luteolin 7-O-glucuronide, which both have numerous pharmacological activities, were determined. This indicates that thyme postdistillation waste material extracts could be used for isolation of dominant compounds or as addities in pharmaceutical and food industry.
Part of the book: Concepts, Compounds and the Alternatives of Antibacterials