Melaleuca armillaris Sm. essential oil as adjuvant for erythromycin in acid enviroment against Staphylococcus aureus

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

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

INTRODUCTION. Erythromycin (ERY) is a natural macrolide; is considered an alternative for treatment of mastitis caused by penicillin-resistant S. aureus. Macrolides reach high intracellular concentrations, accumulate within phagocytes but they are rapidly inactivated in acid environments. The actual efficacy of bacterial killing within cells has not been unambiguously demonstrated (Lucas et al. 2007).The treatment against microorganisms able to maintain and thrive in the intracellular environment face us to a hard challenge. It could be useful finding an adjuvant that improves the antimicrobial (ATM) activity at this level. Essential oils (EO) are a relevant herbal alternative in ATM therapies. Melaleuca armillaris Sm. is a Myrtaceae rich in EO and this has shown great ATM activity (Amri et al. 2012). Essential oil of M. armillaris alone or in combination with antimicrobial could be a new choice for treatment of microbial infections. So, our aim was to evaluate the existence of a synergistic effect between the EO and ERY emulating an intracellular acid environment (pH 5) in look up for a strategy against staphylococcal infections of difficult resolution. MATERIALS AND METHODS. The EO was obtained by steam distillation and it was tested against the strains of S. aureus resistant to ERY (n=3) and susceptible wild type strains of S. aureus (n=3), both isolated from Holstein cows. S. aureus ATCC 29213 was the control strain. The Minimum Inhibitory Concentration (MIC) of ERY and the EO alone and in combination was determined by microdilution in broth (CLSI, 2013) at pH 7.4 and 5. The interaction ERY-EO was evaluated by checkerboard technique. The Fractional Inhibitory Concentration (FIC) was established. RESULTS AND CONCLUSIONS. ERY decreased its activity in acid medium (MIC is increased 16 times), but when it was combined with the EO maintained the therapeutic level of antibiotic against susceptible S. aureus strains. The combination of EO with ERY, decreased the MIC of the antibiotic against all resistant strains and showed partial synergistic effect with FIC´s ranging between 0.50 and