True Laurel, bay tree, bay laurel or Grecian Laurel Laurus nobilis is a shrub of the Lauraceae family native to the Mediterranean basin and cultivated mainly in Europe and the United States. It is a symbol of peace and victory, which explains its use for making wreaths.
Its essential oil is obtained from the leaves. It has a lot of therapeutic effects.
It is used in many forms: orally, by diffusion, by inhalation or by skin application. It is traditionally used for canker sores, gingivitis, toothaches, ulcers, bedsores, boils, abscesses, arthritis, rheumatism, bronchitis, psoriasis … Laurel essential oil contains about 30% of 1,8-cineole, a monoterpene also known as eucalyptol.
Laurel essential oil has been shown to be effective in vitro againstStaphylococcus aureus, S. epidermidis, two strains of Bacillus cereus, Escherichia coli, Streptococcus faecalis, Enterococcus faecalis and Pseudomonas aeruginosa. the effectiveness of this essential oil on E.Coli is comparable to that of tetracyclines and even greater on S. Aureus. While 1 to 2µL are more effective in all cases than tetracyclines.
The anti-bacterial effect is more effective with the whole essential oil than with its different constituents used separately, which suggests a synergy of the different constituents. Eucalyptol plays a major role in its effectiveness, particularly through its interactions with oxygenated terpenes (CHMIT & al., 2014 ; CAPUTO & al., 2017 ; NABILA & al. , 2020).
In 2017, CAPUTO & al. have proven the anti-fungal effect in vitro of noble laurel essential oil against Aspergillus niger, A. versicolor, Penicillium citrinum and P. expansum, latter being the most sensitive (CAPUTO & al., 2017). It is also effective in vitro against Aspergillus flavus. A concentration of 1.5 mg/ml causes a 76.1% inhibition of mycelium formation by the fungus. A concentration of 1.75 mg/ml or more causes a 100% inhibition of the mycelium growth. This effect is associated with morphological changes in hyphae and membrane damage caused by eucalyptol. Laurel also reduces the production of alpha toxin B1 by fungi (BELASLI & al. , 2020).
This oil also allows the inhibition of biofilm formation by Candida albicans with an effect comparable to that of nystatin. This effect is caused by monoterpenes and sesquiterpenes which weaken the cell envelope and modify membrane permeability (PEIXOTO & al., 2018).
A concentration of 200µL/ml of Laurel essential oil inhibits 29% of Rhipicephalus microplus tick egg outbreaks. Larvicidal activity is also observed to be more effective than adulticidal activity against this cattle parasite. This is because adults have a thicker cuticle than larvae, making penetration of the essential oil more difficult (MARIANO FERNANDEZ & et al., 2018).
L. nobilis has acaricidal activity against Psoroptes cuniculi. A concentration of 10% in fact causes a mortality of 73% of adult parasites. At half the concentration, the mortality is of 51% (MACCHIONI & al., 2008).
A 2020 study proved that laurel essential oil has an effect on SARS-Cov (LOIZZO & al., 2008).
Laurel essential oil effectively inhibits DPPH, hydroxyl and superoxide radicals, as well as hydrogen peroxide. Eucalyptol is more effective on its own in inhibiting lipid peroxidation (SAHIN BASAK & al., 2013).
