Antimicrobial activity of harzianic acid against Staphylococcus pseudintermedius.

The emerging concern about the increase of antibiotic resistance has encouraged research efforts to develop effective alternatives to counteract bacterial infections. Herein, we studied a new perspective to therapeutic treatment against Staphylococcus pseudintermedius, an opportunistic pathogen documented as the major cause of skin, ear, and post-operative bacterial infections in dogs and cats. Antimicrobial activity of secondary metabolites produced by selected microbial strains belonging to Trichoderma, Talaromyces, Clonostachys and Coniothyrium fungal genera has been tested against S. pseudintermedius. Several extracts, particularly those obtained from Trichoderma harzianum E45 and ET45, showed a significant antimicrobial activity towards S. pseudintermedius methicillin-resistant (MRSP) and methicillin-susceptible (MSSP) strains. Bioassay-guided fractionation of E45 and ET45 extracts allowed to isolate harzianic acid as the major compound responsible for biological activities (e.g. antimicrobial, antibiofilm formation and biofilm disaggregation).