Pharmacodynamic effects of the essential oil of Melaleuca armillaris combined with rifaximin or erythromycin against Staphylococcus aureus

BULDAIN, DANIEL; BUCHAMER, ANDREA; MARCHETTI, LAURA; ALIVERTI, FLORENCIA; BANDONI, ARNALDO; MESTORINO, NORA

Congreso; 14th International Congressof the European Association for Veterinary Pharmacology and Toxicology; 2018

INTRODUCTIONThe excessive use of antibiotics has contributed to an alarming situation in which antimicrobial therapy is not effective for the treatment of pathogens that have acquired resistance. This problem requires the search of new alternatives on antimicrobial therapy to face it. Another choice of antimicrobial resource is represented by the essential oils (EO) (1). The family of Myrtaceae has a large number of plant species rich in EO. Melaleuca armillaris Sm. belongs to this family and there is evidence in many investigations that its EO has antimicrobial activity (2). So our objective was to evaluate the existence of a possible synergistic effect between the EO and erythromycin (ERY) or rifaximin (RIF) at different pH conditions. This is in order to emulate the activity of each antibiotic against S. aureus at the environment intracellular looking for maximize efficacy. MATERIALS AND METHODSThe EO was obtained by steam distillation and its composition was analyzed by a GC?FID?MS. We worked with susceptible S. aureus strains wild type (n=3) isolated from Holstein cows. S. naureus ATCC 29213 was the reference strain. The Minimum Inhibitory Concentration (MIC) of ERY, RIF and the EO alone and in combination was determined by microdilution in broth (CLSI, 2013) at pH 7.4; 6.5 and 5. The checkerboard technique was applied to evaluate the interaction ERY-EO and RIF-EO. The Fractional Inhibitory Concentration (FIC) was established. RESULTS AND CONCLUSIONS The most abundant components found in the EO were 1.8 cyneole (72.3 %), limonene (7.8 %) and α-pinene (6 %). RIF had high potency (0.032 µg/mL) against S. aureus at different pH conditions. Combining RIF with the EO, we found a synergic effect where the antibiotic was potentiated in greater magnitude at pH 5 (the MIC decreased 8-fold with 1.6 µL/mL of EO). However, the activity of ERY decreased at lower pH (16-fold, 0.5 vs 8 µg/mL at pH of 7.4 and 5 respectively), but its potency was enhancing by adding the EO, maintaining the antibiotic in active concentrations from the pharmacodynamic point of view. Those results are important findings for the treatment of staphylococcal infections of difficult resolution, because with the emergence of antimicrobial resistance of S. aureus to conventional antibiotics the treatment options for infections have become limited.