Antimicrobial effect of Thymus capitatus and Citrus limon var. pompia as raw extracts and nanovesicles

In view of the increasing interest in natural antimicrobial molecules, this study screened
the ability of Thymus capitatus (TC) essential oil and Citrus limon var. pompia (CLP) extract as raw
extracts or incorporated in vesicular nanocarriers against Streptococcus mutans and Candida albicans.
After fingerprint, TC or CLP were mixed with lecithin and water to produce liposomes, or different
ratios of water/glycerol or water/propylene glycol (PG) to produce glycerosomes and penetration
enhancer vesicles (PEVs), respectively. Neither the raw extracts nor the nanovesicles showed
cytotoxicity against human gingival fibroblasts at all the concentrations tested (1, 10, 100 μg/mL).
The disc diffusion method, MIC-MBC/MFC, time-kill assay, and transmission electron microscopy
(TEM) demonstrated the highest antimicrobial potential of TC against S. mutans and C. albicans. The
very high presence of the phenol, carvacrol, in TC (90.1%) could explain the lethal effect against the
yeast, killing up to 70% of Candida and not just arresting its growth. CLP, rich in polyphenols, acted
in a similar way to TC in reducing S. mutans, while the data showed a fungistatic rather than a
fungicidal activity. The phospholipid vesicles behaved similarly, suggesting that the transported
extract was not the only factor to be considered in the outcomes, but also their components had an
important role. Even if other investigations are necessary, TC and CLP incorporated in nanocarriers
could be a promising and safe antimicrobial in caries prevention.