This study is based on the hypothesis that various extracts from Usnea barbata L. have antibacterial action. Six lichen extracts of different concentrations in: 96% ethanol, acetone and water, have been studied. Their inhibitory action was tested by adapting a diffusimetric antibiogram, made for three pathogenic Gram-positive and Gram-negative bacteria from the oro-dental cavity: Staphylococcus aureus, Pseudomonas aeruginosa and Escherichia coli.
Our results showed that on Staphylococcus aureus, acetone and ethanolic Usnea barbata L. extracts have a great antibacterial action. On Gram-negative bacteria, in the zone of inhibition of the acetone and ethanolic extracts from Usnea barbata L., the development of resistant mutant strains was observed. On all the studied pathogenic bacteria: aqueous extract from Usnea barbata L. is totally inactive.
In conclusion, in oro-dental infections where strains of Staphylococcus are involved, acetone and ethanolic Usnea barbata L. extracts could be very effective as auxiliary treatment, together with classic antibiotics.