Essential oil from Origanum vulgare completely inhibits the growth of multidrug-resistant Cystic Fibrosis pathogens

Objectives: The aim of this study was to test the Essential Oil (EO) from Origanum vulgare for antimicrobial activity in vitro, against five of the major human opportunistic pathogens, responsible for respiratory infections in Cystic Fibrosis (CF) patients, that is Methicillin-resistant Staphylococcus aureus, Pseudomonas aeruginosa, Stenotrophomonas maltophilia, Achromobacter xylosoxidans and Burkholderia cepacia complex. Methods: Antibiotic susceptibility of each strain was previously tested by standard disk diffusion method. The antibacterial activity of O. vulgare EO against a panel of 100 bacterial strains was evaluated, with MIC and MBC determined by microdilution method. Results: Most strains, almost all of them, resulted resistant to multiple antibiotics and could be defined as MultiDrug-Resistant (MDR). The O. vulgare Essential Oil (OEO) was effective against all tested strains although at a different extent. The MBC and MIC of OEO for strains of S. aureus were lower or equal to 1.5% and 0.50% (Vol/Vol), respectively; for P. aeruginosa strains, were lower or equal to 1% (Vol/Vol); for strains of A. xylosoxidans, were lower or equal to 1% and 0.50% (Vol/Vol); and for S. maltophilia and Bcc strains were lower or equal to 0.25%. Conclusions: The results from this study suggest that OEO may exert a role as antimicrobials in the treatment of CF infections.