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

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

Wroclaw

Congreso; 14thInternational Congress of EAVPT; 2018

EAVPT

INTRODUCTION. The excessive use of antibiotics has contributed to an alarming situation in which antimicrobial therapy is not effective in the treatment of pathogens that have acquired resistance. The problem of resistance requires the search for new alternatives on antimicrobial therapy to face it. A great antimicrobial resource is represented by the essential oils (EO) (Yap et al., 2014). The family of Myrtaceae has a large number of plant species rich in EO. Melaleuca armillaris Sm. belongs to this family and its EO has shown great antimicrobial activity in many investigations (Amri et al., 2012). 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, in order to emulate the activity of each antibiotic against S. aureus at the environment intracellular looking for maximize efficacy. MATERIALS AND METHODS. The EO was obtained by steam distillation and its composition was analyzed by a GC?FID?MS. We worked with wild type susceptible S. aureus strains (n=3) isolated from Holstein cows and S. aureus ATCC 29213 as 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 -pinene (6 %). RIF had high potency (0.032 g/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 L/mL of EO). However ERY diminished its activity at lower pH (sixteen times, 0.5 vs 8 µg/mL at pH of 7.4 and 5 respectively), although its potency was also enhancing by added the EO maintaining the antibiotic in active concentrations from the pharmacodynamic point of view. Those results are hopeful 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