Combination of Cloxacillin and Essential Oil of Melaleuca armillaris as an Alternative Against Staphylococcus aureus

MARCHETTI, MARÍA L.; MESTORINO, NORA; BULDAIN, DANIEL; ALIVERTI, FLORENCIA; BUCHAMER, ANDREA V.; BANDONI, ARNALDO

Frontiers in Veterinary Science

Frontiers

Lugar: Lausanne; Año: 2018 vol. 5

The emergence of resistance to antibiotics has been favored by abuse in the applicationof antimicrobials in human and animal medicine. Essential oils are a great resourceto deal with this crisis. Melaleuca armillaris belongs to the family of Myrtaceae, richin species with essential oils. Plant extracts has shown antimicrobial activity in manyinvestigations. Cloxacillin (CLOX) is an antibiotic widely used in veterinary medicineagainst Staphylococcus aureus. Our aim was to assess pharmacodynamic interactionestablished by combining essential oil of M. armillaris (EO) with CLOX in search of asynergistic effect that maximizes the antibacterial activity against S. aureus. The EO wasobtained by steam distillation and its composition was analyzed by a GC?FID?MS. Themost abundant components in the EO were 1.8 cineole (72.3%), limonene (7.8%). andα-pinene (6%). We worked with wild type S. aureus strains (n = 3) isolated from Holsteincows, and S. aureus ATCC 29213 as the reference strain. The Minimum InhibitoryConcentration (MIC) of CLOX, EO and the combination was determined by microdilutionin broth at pH 7.4; 6.5 and 5.0. The checkerboard method was applied to evaluatethe interaction between CLOX and EO. The Fractional Inhibitory Concentration index(FIC) was established. From those combinations that yielded the lowest FIC values, weevaluated the index of antibacterial activity (E), established as the difference between theLog10 values of the number of viable bacteria at the initial (nt0) and at the end of the test(nt24). So, time-killing curves with CLOX and EO/CLOX combination at 0.5, 1, 2, 4, and 8fold the MIC in broth at pH 7.4; 6.5 and 5.0 were prepared. We considered Bacteriostaticeffect (E = 0) Bactericidal effect (E = −3) and Effect of virtual eradication of bacteria(E = −4). A clear synergic activity between the EO and the CLOX was demonstrated,which allows reducing the MIC of β-lactam against S. aureus. This interaction wasfavored by acidification of the medium, where lower concentrations of CLOX achieved abactericidal effect, close to virtual eradication, in the presence of small amounts of EO.