Cinnamomum cassia and Syzygium aromaticum Essential Oils Reduce the Colonization of Salmonella Typhimurium in an In Vivo Infection Model Using Caenorhabditis elegans.

The regulation of intestinal colonization in livestock by means of non-bactericidal additives is an important management lever for zoonotic bacteria such as Salmonella spp. Caenorhabditis elegans is proposed here as a model for the evaluation of five essential oils (EOs) as anti-colonization products against Salmonella Typhimurium. An evaluation of the toxicity of EOs for C. elegans showed LD50 values ranging from 74.5 ± 9.6 µg/mL for Cinnamomum cassia (CEO) to 271.6 ± 14.9 µg/mL for Syzygium aromaticum (SyEO). Both EOs significantly inhibited bacterial colonization in the digestive tract of C. elegans with reductions of 0.88 and 0.70 log CFU/nematode at nontoxic concentrations of 50 µg/mL and 150 µg/mL, respectively. With the minimal bactericidal concentrations of CEO and SyEO against S. Typhimurium being 312.5 µg/mL and 625 µg/mL, respectively, an antibacterial effect can be excluded to explain the inhibition of the bacterial load. The anti-colonizing activity of these two EOs could, however, be related to an inhibition of the swimming motility, which was significantly reduced by 23.47% for CEO at 50 µg/mL and 19.56% for SyEO at 150 µg/mL. This study shows the potential of C. elegans as a predictive in vivo model of anti-colonizing activities that is suitable for the evaluation of essential oils.

Evaluation of immunomodulatory activities of essential oils by high content analysis.

Nowadays, research concerning immunomodulatory products are of great interest, particularly in the treatment of inflammatory diseases or the prevention of infectious diseases. These activities are usually evaluated on cell cultures, by tracking different factors requiring dedicated manipulation. Evaluation of the immunomodulatory activities of essential oils and pure compounds using several technics adapted to high content analysis is described in this study. This approach allows a multiparametric evaluation on a single cell batch, in order to obtain an overall response. The developed method is based on the simultaneous evaluation of phagocytosis, production of iNOS and secretion of IL-6, induced by contact of RAW 264.7 cells with LPS. The results highlight the immunomodulatory activities of cinnamon and clove essential oils. They also provide information, particularly concerning the inhibitory activity of mint essential oil, which inhibits the LPS-induced phagocytosis of RAW 264.7 cells by 42%, at 100 µg/ml. This work presents for the first time the adaptation of high content analyses for the monitoring of immunomodulatory activities of essential oils. This protocol could be adjustable to other cell types and supplemented by the evaluation of additional parameters.