Antibacterial and Antifungal Activity of Secondary Metabolites of Teucrium Species

Abstract

Teucrium species are known for their medicinal properties and have exhibited different biological activities including broad-spectrum antimicrobial activity. Considering that Teucrium species produce various bioactive compounds (phenolic acids, flavonoids, saponines, alkaloids, monoterpenes, neo-clerodane diterpenes, sesquiterpenes, essential oils) they could be an important source of new antimicrobial compounds. The expanding of knowledge on the antimicrobial plant compounds has opened wide opportunities for their application in medicine, pharmacy, and food industry. Accordingly, the aim of this chapter was to collect and summarize the results of antimicrobial (antibacterial and antifungal) studies. The results for 44 Teucrium species were processed including both the activity of different types of plant extracts and essential oils. Antimicrobial properties were based on in vitro determination of zones of growth inhibition and minimal inhibitory concentrations, using diffusion and dilution method. Teucrium species established broad-spectrum antimicrobial activity. Generally, the species were more active against Gram-positive than Gram-negative bacteria and fungi. The essential oils were more potent than plant extracts. The following Teucrium species exhibited a promising antimicrobial activity: plant extracts of Teucrium flavum, T. fruticans, T. siculum, T. yemense, T. sokotranum, T. persicum and T. scordium, especially against Gram-positive bacteria, and essential oils from Teucrium orientale, T. africanum, T. ramosissimum, T. mascatence, T. yemense, T. massiliense and T. scordonia. Teucrium polium was one of the most tested Teucrium species and has exhibited pronounced activity. The activity was observed against important pathogenic bacteria (Staphylococcus sp., Bacillus sp., Enterococcus sp., Streptococcus sp., Escherichia coli, Pseudomonas aeruginosa, Klebsiella pneumoniae, Salmonella sp.) and fungi (Candida sp., Trychophyton sp.). In the last 20 years, the significant database of antimicrobial properties of Teucrium species is formed. However, the mechanisms of activity are still poorly explored. Only with exact knowledge of these mechanisms, it will be possible to develop a new generation of standardized, effective biopreparations. Future studies on bioavailability, pharmacodynamics, and mechanisms of action will contribute to the development of new Teucrium antimicrobial agents.