The influence of usnic acid on the P. aeruginosa and s. aureus biofilms development

• Published in: Microbial ecology in health and disease Vol. 20; no. 3; p. 160
• Main Authors: Lazar, V, Chifiriuc, M C, Oprea, E, Bucur, M, Iacob, M, Larion, C, Ekene, O C, Cercasov, C
• Format: Journal Article
• Language: English
• Published: 01.05.2008
• Subjects: Pseudomonas aeruginosa; Staphylococcus aureus; Usnea
• ISSN: 0891-060X; 1651-2235

Introduction: The pathogenicity of biofilms formed by opportunistic pathogens is magnified by the increased resistance or tolerance to antimicrobials. It is already known that some lichens, algae and plants are producing soluble metabolites interfering with QS mechanisms developed by sessile bacteria grown in biofilms. Usnic acid, a secondary lichen metabolite, possess antimicrobial activity against a number of planktonic bacteria, and, as many other secondary lichen metabolites, offers protection to lichen communities against the adherent microorganisms. The purpose of this study was to investigate the efficiency of usnic acid on the P. aeruginosa and S. aureus biofilm development on inert substrata (plastic wells, cardiovascular catheters) and cellular (HeLa cell line) substrata. Material and methods: The usnic acid was extracted from the lichen Usnea barbata and tested by two simple models for the development of artificial, monospecific biofilms in liquid and solid media were used: 1) the bacterial cells were immobilized in an agar matrix similar to the natural biofilm polysaccharidic mathrix, adapted for the study of biofilm sensitivity to different antimicrobial products; 2) the biofilms were grown in microplates with/without catheter sections and different usnic acid concentrations, the biofilms being thereafter fixed, colored, resuspended and quantified by spectrophotometry. Results: Although a quantifiable antimicrobial activity against planktonic Gram-negative bacteria was not observed, usnic acid inhibited the development of both P. aeniginosa and S. aureus in biofilms on all tested substrata, rendering them sensitive to usual doses of antimicrobials, such metabolites being studied as QS inhibitors.