Chemical Composition and Synergistic Antimicrobial Effects of Essential Oils From Four Commonly Used <i>Satureja</i> Species in Combination With Two Conventional Antibiotics

The chemical composition and the antimicrobial potency of four Satureja essential oils (EOs), and their synergism with two antimicrobials have been investigated. Gas chromatography (GC) and GC/mass spectrometry analysis showed that S. alpina EO was predominated by pulegone (88.8%), while pulegone (38.6%) and menthone (30%) were the major constituents of S. calamintha EO. S. montana and S. hortensis EOs were dominated by carvacrol (50.8%-32.8%), γ-terpinene (18.5%-40.1%), and p-cymene (8.2%-7.3%), respectively. The antimicrobial activity showed that S. montana and S. hortensis EOs exhibited potent activity (minimal inhibitory concentration and minimum microbiocidal [bactericidal and candidacidal] concentrations = 0.07-4.46 mg/mL for bacteria, and 0.27-1.11 mg/mL for Candida). All EOs showed high synergism with gentamicin against bacteria (gains ranged between 4- and 512-fold). Interestingly, this synergism was pronounced against the Gram-negative bacteria Escherichia coli and Pseudomonas aeruginosa. Regarding the association with amphotericin B, synergistic and additive effects were recorded depending on the strain tested.