Abstract
This study presents, for the first-time, the results of a study on the hydrodynamic diameter of essential oils (EOs) of basil and lavender in water, and solutions of EOs of basil (B) and lavender (L) and hydroxyapatite (HAp). The possible influence of basil and lavender EOs on the size of hydroxyapatite nanoparticles was analyzed by Scanning Electron Microscopy (SEM). We also investigated the in vitro antimicrobial activity of plant EOs and plant EOs hydroxyapatite respectively, against Gram-positive bacteria (methicillin-resistant Staphylococcus aureus1144 (MRSA 1144) and S. aureus 1426) and Gram-negative bacteria (Escherichia coli ATCC 25922 and Escherichia coli ESBL 4493). From the autocorrelation function, obtained by Dynamic Light Scattering (DLS) measurements it was observed that basil yielded one peak at an average hydrodynamic diameter of 354.16 nm, while lavender yielded one peak at an average hydrodynamic diameter of 259.76 nm. In the case of HAp nanoparticles coated with basil (HApB) and lavender (HApL) essential oil, the aggregation was minimal. We found that the lavender EO exhibited a very good inhibitory growth activity (MIC values ranging from <0.1% for E. coli reference strain to 0.78% for S. aureus strains). The biological studies indicated that HapL material displayed an enhanced antimicrobial activity, indicating the potential use of HAp as vehicle for low concentrations of lavender EO with antibacterial properties. Flow cytometry analysis (FCM) allowed us to determine some of the potential mechanisms of the antimicrobial activities of EOs, suggesting that lavender EO was active against E. coli by interfering with membrane potential, the membrane depolarization effect being increased by incorporation of the EOs into the microporous structure of HAp. These findings could contribute to the development of new antimicrobial agents that are urgently needed for combating the antibiotic resistance phenomena.
Highlights
Recent advances in medicine and biotechnology have not been able to overcome the rapid and ongoing worldwide emergence and spread of drug resistant microorganisms
The most abundant components identified in basil and lavender essential oils (EOs) are presented in Tables 1 and 2
The results of the analysis revealed that the dominant components of the lavender EO samples were represented by the oxygenated monoterpenes group
Summary
Recent advances in medicine and biotechnology have not been able to overcome the rapid and ongoing worldwide emergence and spread of drug resistant microorganisms. This fact has stimulated the search for new types of effective and nontoxic antimicrobial agents amongst natural compounds which are found in aromatic plants, and which have been previously used in cosmetics, folk medicine, and aromatherapy [1]. Beyond their antibacterial properties [11], EOs have been reported to exhibit antiviral [12], antimycotic [13], antioxigenic [14], antiparasitic [15], and insecticidal [16] properties
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