Modeling the Growth and Death of Staphylococcus aureus against Melaleuca armillaris Essential Oil at Different pH Conditions

Abstract

Essential oils (EO) are a great antimicrobial resource against bacterial resistance in public health. Math models are useful in describing the growth, survival, and inactivation of microorganisms against antimicrobials. We evaluated the antimicrobial activity of Melaleuca armillaris EO obtained from plants placed in the province of Buenos Aires (Argentina) against Staphylococcus aureus. The minimum inhibitory and bactericidal concentrations were close and decreased, slightly acidifying the medium from pH 7.4 to 6.5 and 5.0. This result was also evidenced by applying a sigmoid model, where the time and EO concentration necessaries to achieve 50% of the maximum effect decreased when the medium was acidified. Moreover, at pH 7.4, applying the Gompertz model, we found that subinhibitory concentrations of EO decreased the growth rate and the maximum population density and increased the latency period concerning the control. Additionally, we established physicochemical parameters for quality control and standardization of M. armillaris EO. Mathematical modeling allowed us to estimate key parameters in the behavior of S. aureus and Melaleuca armillaris EO at different pH. This is interesting in situations where the pH changes are relevant, such as the control of intracellular infections in public health or the development of preservatives for the food industry.

In vitro synergistic interaction between Melaleuca armillaris essential oil and erythromycin against Staphylococcus aureus isolated from dairy cows

“…A sample of the M. armillaris plants used was deposited in the LPAG Herbarium of the Faculty of Agrarian and Forestry Sciences, UNLP ( 30 ). As was described in previous works ( 27 – 29 ), the EO was dried with sodium sulfate anhydrous, filtered with a cotton funnel, and stored at 4°C in an amber glass bottle. EO composition was characterized by gas chromatography combined with mass spectrometry and flame ionization detection (GC-MS-FID; Agilent, Agilent Technologies, Santa Clara, CA, USA) ( 28 ), and the physicochemical characteristics were determined also ( 27 ).…”

“…The EO was obtained by steam distillation of fresh leaves and herbaceous branches of M. armillaris plants from the surroundings of Coronel Brandsen town (latitude 35 (28), and the physicochemical characteristics were determined also (27).…”

“…Melaleuca armillaris EO had antimicrobial activity against S. aureus isolated from cows when it was applied alone ( 26 , 27 ) and in combination with antibiotics like cloxacillin ( 28 ) and rifaximin ( 29 ). Therefore, the objective of this study was to combine this EO with ERY evaluating their interaction against S. aureus at different pH emulating pH conditions at the extra and intracellular level.…”

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

“…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].…”

“…The E index values vs. ERY concentration data was mathematically modeled using a sigmoid model similar to a maximum response model [27,53,54]. In this way we could analyzed deeply the effect of EO in the antimicrobial activity of ERY against S. aureus under the different conditions evaluated.…”