Antibacterial activity of Lithraea molleoides Hook et Arn. and Poiretia latifolia Vogel essential oils combined with gentamicin on foodborne disease-causing bacteria

Abstract

The synergy between antimicrobial substances present in plant essential oils, with the goal of decreasing the required dosage of synthetic antibiotics is a viable strategy in the control of resistant pathogens. The present work aimed to characterize the chemical composition of EOs from Lithraea molleoides Hook et Arn. and Poiretia latifolia Vogel, as well as to evaluate their antimicrobial activities against some foodborne disease causing bacteria by determining minimum inhibitory concentration (MIC) in microplates, and their synergistic effects with a synthetic antibiotic by a checkerboard assay. The main compounds found in each EO were (E)-nerolidol (19.23%), (E)-caryophyllene (12.17%) and myrcene (11.52%) for L. molleoides, and carvone (61.81%), limonene (31.33%) and β-pinene (2.28%) for P. latifolia. Both EOs inhibited the tested microorganisms in one of the concentrations evaluated. Escherichia coli, Salmonella enteritidis, Staphylococcus aureus, and Bacillus cereus were inhibited with 20 mg mL−1 of L. molleoides EO. EO of P. latifolia inhibited B. cereus and E. coli growth at lower concentrations (10 mg mL−1 and 2.5 mg mL−1, respectively) and showed higher activity against E. coli, a Gram-negative bacteria. The highest synergistic interaction (IFIC <0.5) with the tested antibiotic was observed in P. latifolia EO, which reduced the MIC of gentamicin up to three times against all microorganisms except for E. coli (FICI = 3) which indicated indifference in their interaction. The combination of the antibiotic and L. molleoides EO showed synergism against B. cereus (IFIC = 0.4 and 0.5) but was indifferent to the remaining microorganisms (IFIC = 2.5, 1 and 1.5). These findings demonstrate the potential of these EOs as natural antibacterial agents that can contribute to reducing the adverse effects attributed to gentamicin.