Ambuic acid is a cyclohexanone originally isolated from Pestalotiopsis and Monochaetia species that has phytopathogenic antifungal, quorum sensing inhibitory, and antibacterial activities. It is active against P. ultimum (MIC = 7.5 &#181g/ml) and inhibits the growth of a variety of other phytopathogenic fungi, including F. solani, H. sativum, and C. gramineum, but not P. oryzae, R. solani, or B. cinerea. Ambuic acid inhibits the biosynthesis of cyclic peptides involved in quorum sensing, including gelatinase biosynthesis-activating pheromone (GBAP) in E. faecalis, autoinducing peptide I (AIP-I) in S. aureus, and LsrD698 and LsrD826 in L. innocua. It suppresses abcess formation in a mouse model of skin infection induced by methicillin-resistant S. aureus (MRSA) when administered at a dose of 5 &#181g and decreases the activity of the agr quorum sensing system in an in vivo reporter assay.