Cosmetics, like any product containing water and organic/inorganic compounds, require preservation against microbial contamination to guarantee consumer’s safety and to increase their shelf-life. The microbiological safety has as main goal of consumer protection against potentially pathogenic microorganisms, together with the product’s preservation resulting from biological and physicochemical deterioration. This is ensured by chemical, physical, or physicochemical strategies. The most common strategy is based on the application of antimicrobial agents, either by using synthetic or natural compounds, or even multifunctional ingredients. Current validation of a preservation system follow the application of good manufacturing practices (GMPs), the control of the raw material, and the verification of the preservative effect by suitable methodologies, including the challenge test. Among the preservatives described in the positive lists of regulations, there are parabens, isothiasolinone, organic acids, formaldehyde releasers, triclosan, and chlorhexidine. These chemical agents have different mechanisms of antimicrobial action, depending on their chemical structure and functional group’s reactivity. Preservatives act on several cell targets; however, they might present toxic effects to the consumer. Indeed, their use at high concentrations is more effective from the preservation viewpoint being, however, toxic for the consumer, whereas at low concentrations microbial resistance can develop.

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This study describes the chemical composition and the antibacterial, antifungal and antioxidant activities of the essential oil extracted from aerial parts of the Algerian Eryngium tricuspidatum L., obtained by hydrodistillation and analysed by using the combination of gas chromatography (GC) and GC/mass spectrometry. A total of 63 compounds were identified accounting for 93.1% of the total oil. Chemical composition of oil was characterised by a high proportion of oxygenated sesquiterpenes (49.6%) among which α-bisabolol (32.6%) was the predominant compound. The sesquiterpene hydrocarbons represent the second major fraction (31.9%) with α-curcumene (6.5%) being the predominant one. Antibacterial and antifungal activities of the oil were tested using the micro-well determination of minimum inhibitory concentration (MIC) assay against eleven bacteria and two Candida species. It was found that the aerial parts of E. tricuspidatum exhibited interesting antibacterial and anticandidal activities (MIC = 9 μg/mL against several strains of bacteria and MIC = 4.6 μg/mL against Candida albicans). The antioxidant effect of this oil was evaluated using the 2,2-diphenyl-l-1-picrylhydrazil (DPPH) and ferric reducing antioxidant power (FRAP) assays. Results revealed significant activities (DPPH method: IC₅₀ = 510 μg/mL; FRAP assay: reducing power of oil increases from 0.0188 at 5 μg/mL to 0.5016 at 1000 μg/mL).

These results suggest that the Algerian L. inermis plant has antifungal activity that can be related to the presence of lawsone in the leaves plant. The results can be exploited largely in research of new antifungal drugs.

The present in vitro study examined the effects of the quorum-sensing molecules farnesol and tyrosol on the development of Candida albicans biofilm in order to elucidate their role as novel adjuvants in oral hygiene. The investigation was conducted in C. albicans ATCC 10231 and C. albicans isolates from dentures and was performed in flat-bottomed 96-well polystyrene plates. Yeast growth and their capacity to form biofilms were evaluated following 24 and 48 h incubations at 37°C in Sabouraud broth supplemented with 0.001–3 mM farnesol and/or 1–20 mM tyrosol. Yeast growth was assessed by turbidimetry and biofilms were quantitated by crystal violet staining, under aerobic and anaerobic conditions. The viability of the fungal cells was controlled by the culture of planktonic cells and by examination of the biofilms using fluorescence microscopy following staining with fluorescein diacetate and ethidium bromide. Farnesol at 3 mM exerted a stronger action when added at the beginning of biofilm formation (>50% inhibition) than when added to preformed biofilms (<10% inhibition). Similarly, tyrosol at 20 mM had a greater effect on biofilm formation (>80% inhibition) than on preformed biofilms (<40% inhibition). Despite significant reductions in attached biomass, yeast growth varied little in the presence of the investigated molecules, as corroborated by the turbidimetry, culture of supernatants on solid culture medium followed by counting of colony-forming units and viability tests using fluorescence microscopy. At the highest tested concentration, the molecules had a greater effect during the initial phases of biofilm formation. The effect of farnesol during anaerobiosis was not significantly different from that observed during aerobiosis, unlike that of tyrosol during anaerobiosis, which exhibited slightly reduced yeast biofilm inhibition. In conclusion, the present study demonstrated the specific anti-biofilm effect, independent of fungicidal or fungistatic action, of farnesol and tyrosol, as tested in C. albicans ATCC 10231 and 6 strains isolated from dentures. Prior to suggesting the use of these molecules for preventive purposes in oral hygiene, further studies are required in order to clarify the metabolic pathways and cellular mechanisms involved in their antibiofilm effect, as well as the repercussions on the oral microbiome.