Antibacterial Properties of Origanum vulgare and Eucalyptus staigeriana Essential Oils Single or in Combination With Cloxacillin Against Corynebacterium pseudotuberculosis

Abstract

Caseous lymphadenitis is a chronic infectious disease caused by Corynebacterium pseudotuberculosis that affects small ruminants, resulting in significant economic losses. In response, essential oils (EO) have emerged as promising natural alternatives for disease control. The present study evaluated the chemical composition, antioxidant capacity, and antibacterial activity of EO from Origanum vulgare (OVEO) and Eucalyptus staigeriana (ESEO) against C. pseudotuberculosis isolated from Northeastern Brazil. The antibacterial effect was assessed by disk diffusion, minimum inhibitory concentration (MIC), Minimum Bactericidal Concentration, time–kill assays, and combination tests with cloxacillin. Gas chromatography analysis identified carvacrol as the major compound in OVEO, and D‐limonene in ESEO. OVEO demonstrated strong antibacterial efficacy, exhibiting inhibition zones of up to 74 mm and MICs ranging from 31.2 to 250 µg/mL. Both EOs demonstrated bactericidal properties and exhibited additive interactions with cloxacillin (FICi 0.56–1.03). Furthermore, OVEO exhibited strong antioxidant activity (IC50 = 6.89 ± 0.58 µg/mL). These findings underscore the significance of bioactive compounds with antibacterial potential, although further studies are necessary to evaluate their applicability for managing caseous lymphadenitis.