This work extends in vitro screening of antimicrobial activity of the sesquiterpene hydroquinone avarol, a main
secondary metabolite of the Mediterranean sponge species Dysidea avara. The antimicrobial activity was in part evaluated
by microdilution method against selected bacterial and fungal strains. Additionally, the screening included evaluation of
anti-quorum sensing (anti-QS) effects. At a different extent avarol was proven to be active against all the microorganisms
tested (MIC 0.002-0.008 mg/mL and MBC 0.004-0.016 mg/mL; MIC 0.004-0.015 mg/mL and MFC 0.008-0.030 mg/mL;
respectively). This marine natural product also showed moderate anti-QS effects, reducing Pseudomonas aeruginosa
PAO1 biofilm formation (75%), its twitching and protrusions motilities as well as pyocianin production (39%). According to
the best of our knowledge, this is the first report both on avarol anti Gram-negative bacterial activity and anti-QS effects.
Keywords: Anti-quorum sensing effects, Dysidea avara, Gram-negative bacteria, natural product, Pseudomonas aeruginosa PAO1.
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