SUMMARY
Infections caused by strains of bacteria that show resistance to a large number of antibiotics represent one of the leading problems today. The aim of this work is to examine new, natural resources with potential antimicrobial effects. The antibacterial activity of lichen resinoids (Evernia prunastri) was tested against reference strains Staphylococcus aureus ATCC 25923, Staphylococcus epidermidis ATCC 12228, Pseudomonas aeruginosa ATCC 27853, Escherichia coli ATCC 25922 and clinical isolates of bacteria S. aureus, S. epidermidis, P. aeruginosa and E. coli, by the disc-diffusion method. Each 10 µl of resinoid, of different concentrations, was applied to sterile discs with a diameter of 6 mm. The tested resinoid exhibited the most significant antibacterial activity against Pseudomonas aeruginosa ATCC 27853, while it was the weakest against the clinical isolate of Escherichia coli. The results indicate that the tested oakmoss resinoid shows moderate antimicrobial activity against the tested strains.