Potent In Vitro Activity of Citrus aurantium Essential Oil and Vitis vinifera Hydrolate Against Gut Yeast Isolates from Irritable Bowel Syndrome Patients—The Right Mix for Potential Therapeutic Use

Background: Irritable bowel syndrome (IBS) is a functional disorder without any pathological alteration, in which the alterations of the Candida/Saccharomyces ratio of the gut microbiota, the balance of pro and anti-inflammatory cytokines and the brain-gut-microbiome axis are important for the development and progression of IBS. The aim of the study was to identify natural products, including essential oils or hydrolates, which were contextually harmless for the gut beneficial strains (e.g., Saccharomyces spp.) but inhibitory for the pathogenic ones (Candida spp.). Methods: The effectiveness of 6 essential oils and 2 hydrolates was evaluated using microbiological tests, carried out on 50 clinical isolates (Candida, Saccharomyces and Galattomyces species) and 9 probiotic strains (Saccharomyces cerevisiae, Lactobacillus species, Akkermansia muciniphila and Faecalibacterium prausnitzii) and immunological and antioxidant assays. Results: The study led to a mixture based on a 1/100 ratio of Citrus aurantium var. amara essential oil / Vitis vinifera cv Italia hydrolate able to contextually reduce, in a concentration-dependent manner, the ability of Candida species to form hyphal filaments and have an interesting immunomodulatory and anti-oxidant action. This mixture can potentially be useful in the IBS treatment promoting the restoration of the intestinal microbial and immunological balance.