Synergistic Effect of Abietic Acid with Oxacillin against Methicillin-Resistant .

Resin acids are valued in traditional medicine for their antiseptic properties. Among these, abietic acid has been reported to be active against methicillin-resistant (MRSA) strains. In veterinary healthcare, the methicillin-resistant (MRSP) strain is an important reservoir of antibiotic resistance genes including . The incidence of MRSP has been increasing, and treatment options in veterinary medicine are partial. Here, we investigated the antimicrobial and antibiofilm properties of abietic acid against three MRSP and two methicillin-susceptible (MSSP) strains, isolated from diseased pet animals and human wound samples. Abietic acid showed a significant minimal inhibitory concentration (MIC) value ranging from 32 to 64 μg/mL (MRSPs) and 8 μg/mL (MSSP). By checkerboard method we demonstrated that abietic acid increased oxacillin susceptibility of MRSP strains, thus showing a synergistic interaction with oxacillin. Abietic acid was also able to contrast the vitality of treated MSSP and MRSP1 biofilms at 20 μg/mL and 40 μg/mL, respectively. Finally, the compound moderately reduced , and gene expression. In conclusion, the results here reported demonstrate the antimicrobial activity of abietic acid against MRSP and support the use of this compound as a potential therapeutic agent to be used in combinatorial antibiotic therapy.