Antimicrobial and antibiofilm effects of shikonin with tea tree oil nanoemulsion against Candida albicans and Staphylococcus aureus

Abstract

The current work aims to develop a shikonin and tea tree oil loaded nanoemulsion system stabilized by a mixture of GRAS grade surfactants (Tween 20 and monoolein) and a cosurfactant (Transcutol P). This system was designed to address the poor aqueous solubility and photostability issues of shikonin. The authenticity of shikonin employed in this study was confirmed using nuclear magnetic resonance (NMR) spectroscopy. The optimized nanoemulsion exhibited highly favorable characteristics in terms of zeta potential (−23.8 mV), polydispersity index (0.216) and particle size (22.97 nm). These findings were corroborated by transmission electron microscopy (TEM) micrographs which confirmed the spherical and uniform nature of the nanoemulsion globules. Moreover, attenuated total reflectance (ATR) and X-ray diffraction analysis (XRD) analysis affirmed improved chemical stability and amorphization, respectively. Photodegradation studies were performed by exposing pure shikonin and the developed nanoemulsion to ultraviolet light for 1 h using a UV lamp, followed by high performance liquid chromatography (HPLC) analysis. The results confirmed that the developed nanoemulsion system imparts photoprotection to pure shikonin in the encapsulated system. Furthermore, the research investigated the effect of the nanoemulsion on biofilms formed by Candida albicans and methicillin resistant Staphylococcus aureus (MRSA). Scanning electron microscopy, florescence microscopy and phase contrast microscopy unveiled a remarkable reduction in biofilm area, accompanied by disruptions in the cell wall and abnormalities on the cell surface of the tested microorganisms. In conclusion, the nanoencapsulation of shikonin with tea tree oil as the lipid phase showcased significantly enhanced antimicrobial and antibiofilm potential compared to pure shikonin against resistant strains of Candida albicans and Staphylococcus aureus.

Keywords:

• Shikonin
• antibiofilm
• MRSA
• Candida albicans
• nanoemulsion
• tea tree oil
• monoolein

Acknowledgements

The authors are grateful to Department of Science and Technology (DST), Government of India PURSE, CPEPA, FIST and RUSA schemes for strengthening the infrastructure of Guru Nanak Dev University, Amritsar. The authors are also thankful to Department of Pharmaceutical Sciences and Department of Botanical and Environmental Sciences, Guru Nanak Dev University, Amritsar, India for providing the appropriate facilities to carry out the present work. The authors also want to acknowledge Prof. (Dr) Daljit Singh Arora (Professor, Department of Microbiology, Guru Nanak Dev University, Amritsar, India) for providing the clinical isolates of MRSA.

Disclosure statement

The authors report no declaration of interest.

Additional information

Funding

The author(s) reported there is no funding associated with the work featured in this article.