Melaleuca armillaris Essential Oil in Combination With Rifaximin Against Staphylococcus aureus Isolated of Dairy Cows

Abstract

Staphylococcus aureus is the major subclinical mastitis-causing pathogen in dairy cows. In some European and Latin American countries, rifaximin (RIF) is a commonly used therapy at drying off. Phytotherapeutics are alternatives for the treatment of infectious diseases. Melaleuca armillaris essential oil (EO) has been reported as a good antimicrobial against S. aureus. The aim of this work was to investigate, in vitro, the combined effect of EO and RIF to identify a synergic interaction against S. aureus in order to obtain enough information for subsequent pharmacokinetic/pharmacodynamic studies. The minimum inhibitory concentrations (MIC) for RIF, EO, and combinations of these against S. aureus strains were determined at pH 7.4, 6.5, and 5.0, representing intracellular conditions where S. aureus is usually located. The fractional inhibitory concentration index (FIC) and the index of antibacterial activity (E) were evaluated. The MIC of EO at pH 7.4 was 25-12.5 µL/mL and decreased with the acidity of the medium. RIF presented a high antimicrobial activity (0.032 µg/mL) against S. aureus regardless of the pH conditions. Combining RIF with EO, we found a synergic effect. A mix of 0.004 µg/mL of RIF and 12.5 µL/mL of EO led to a virtual eradication effect against wild-type strains at pH 7.4. Media acidification improves the EO/RIF activity, so EO would be a good adjuvant for RIF to treat staphylococcal infections and decrease antimicrobial resistance.

PK/PD Modeling to Assess Rifaximin Clinical Dosage in a Mouse Model of Staphylococcus aureus-Induced Mastitis

“…Buldain made a time-kill curve for the effect of rifaximin on S. aureus ATCC 29213 at pH 5.0. They found an almost 4log 10 CFU/ml reduction in the 10 6 CFU/ml initial inoculum group with 2MIC or higher concentrations of rifaximin; however, rifaximin did not inhibit the growth of bacteria when the concentration was below the MIC (36). These results are consistent with those of the current study, showing that the effect of rifaximin is time dependent.…”

“…In the MIC study, the MIC of rifaximin against S. aureus ranged from 0.031 to 0.125 µg/ml, but was mainly distributed at 0.031 mg/ml, which was similar to results reported in previous papers (36,37). The MIC 50 and MIC 90 were calculated with 0.031 and 0.063 µg/ml, respectively, and the MIC 90 of 0.063 µg/ml was used in the PK/PD model.…”

Erythromycin and <em>Melaleuca armillaris</em> Essential Oil Combination against <em>Staphylococcus aureus</em> Isolated from Dairy Cows

“…This was also reflected in the E-index analysis. Like was observed for other classes of antibiotics like cloxacillin [28] and rifaximin [29], the E-Index vs. antibiotic concentration, show how the curve is shifted towards lower concentrations of ERY in the presence of EO. On the other hand, it is clearly states how the addition of the plant extract favors the scope of the bactericidal effect.…”

“…The combination of M. armillaris EO and ERY was interesting, particularly in the case of wild S. aureus strains resistant to this macrolide. We previously demonstrate the EO antimicrobial activity against S. aureus and the efficacy as adjuvant of cloxacillin [28] and rifaximin [29]. The strains resistant to ERY evaluated in this work (SA78A, SA79A and SA86B) had very high MIC values (1024 g/mL), loosing antimicrobial activity in acid conditions as was mentioned before.…”

“…A sample of the M. armillaris plants used was deposited in the LPAG Herbarium of the Faculty of Agrarian and Forestry Sciences, UNLP [46]. As was described in previous works [27][28][29], the EO was dried with sodium sulphate anhydrous, filtered with a cotton funnel, and stored at 4 °C in an amber glass bottle. EO composition was characterized by GC-MS-FID [28].…”