In vitro antimicrobial activity of extracts and compounds isolated from Cladonia uncialis

Heptane (Hep), diethyl ether (Et2O), acetone (Me2CO) and methanolic (MeOH) extracts, as well as (-)-usnic acid and squamatic acid, were obtained from thallus of Cladonia uncialis (Cladoniaceae). The antimicrobial activities of these extracts, (-)-usnic acid and squamatic acid, were tested against reference strains: Staphylococcus aureus, Escherichia coli and Candida albicans. In addition, Me2CO extract was analysed against 10 strains of Methicillin-resistant S. aureus (MRSA) isolated from patients. All extracts exerted antibacterial activity against the reference strain S. aureus, comparably to chloramphenicol [minimum inhibitory concentration (MIC) = 5.0 μg/mL]. The Me2CO extract exhibited the strongest activity against S. aureus (MIC = 0.5 μg/mL), higher than (-)-usnic acid, whereas squamatic acid proved inactive. The Me2CO extract showed potent antimicrobial activity against MRSA (MIC 2.5-7.5 μg/mL). Also no activity of C. uncialis extracts against E. coli and C. albicans was observed.