In vitro antimicrobial activity of essential oils from Heterothalamus Less. (Asteraceae) against clinically relevant bacterial and fungal species

Abstract

Essential oils are natural, complex, and volatile compounds produced by the secondary metabolism of plants, which often serve as a protection against fungal or bacterial attack. Two species of the Asteraceae family, Heterothalamus alienus (Spreng.) O. Kuntze and Heterothalamus psiadioides Less., are used in folk medicine and recognised for their production of bioactive substances. However, little evidence of their antimicrobial properties currently exists. The aim of this study was to examine the in vitro antimicrobial activity of essential oils from H. alienus and H. psiadioides against clinically relevant bacterial and fungal species. The major chemical components of the essential oils used are terpene substances, of which β-pinene is the major component. Analysis of antibacterial activity was conducted using the disc diffusion method against 22 bacteria (18 gram-positive strains, including 13 enterococci strains resistant or multiresistant to antibiotics, and 4 Gram-negative strains) and 9 fungi (6 yeasts and 3 filamentous fungi). The results indicated that essential oils from Heterothalamus species have a strong antimicrobial effect against gram-positive bacteria and yeasts, variable activity against filamentous fungi, and no activity against gram-negative bacteria. The most prominent results were observed in the sensitivity of Enterococcus faecalis (antibiotic- and multidrug-resistant strains) to the essential oils. In conclusion, this study demonstrates the potential for essential oils from Heterothalamus species for use as both an antiseptic and disinfectant in future approaches to control of clinically relevant gram-positive bacteria and fungi.