Antibacterial, antifungal and antiviral bioactivities of selected Helichrysum species

Helichrysum species are used widely to treat various medical conditions. In the present study, 14 extracts obtained from 7 Helichrysum species such as H. araxinum Takht. ex Kirp., H. armenium DC, H. arenarium, H. pallasii, H. stoechas, H. sanguineum, and H. graveolens (Asteraceae) were screened for their in vitro antibacterial, antifungal, and antiviral activities. Antibacterial and antifungal activities were evaluated against both standard and isolated strains of Gram negative (E. coli, P. aeruginosa, P. mirabilis, K. pneumoniae, A. baumanni) and Gram positive (S. aureus, E. faecalis) bacteria, as well as fungi (Candida albicans, C. parapsilosis) by microdilution method. We performed susceptibility testing according to the Clinical and Laboratory Standards Institute (CLSI; formerly NCCLS). As human pathogens both Herpes simplex virus Type-1 (HSV-1), a DNA virus, and Parainfluenza-3 virus (PI-3), an RNA virus, were employed for antiviral assessment of the water and ethanol extracts of Helichrysum species by using Madin-Darby Bovine Kidney and Vero cell line. All the extracts showed more potent antibacterial activity against Gram positive bacteria (ranging between 16 and 64 μg/mL) than Gram negative (8-64 μg/mL), while showing considerable antifungal activity at 8 μg/mL concentration. Antifungal activities of the extracts were found to be close to antifungal agents in routine clinical use. In particular, all of the ethanolic extracts were found to show better inhibition against S. aureus with a MIC value of 8 μg/mL. In the meantime, ethanolic extracts of H. arenarium and H. armenium DC showed notable antiviral activity against both HSV-1 and PI-3; at a range of 2-32 and 4-64 μg/mL, respectively, by the absence of cytophatic effect. All activities were evaluated at nontoxic concentrations. Helichrysum arenarium and H. armenium DC were found to be the most remarkable species among the tested extracts in terms of bioactivity.