Effects of thymol and carvacrol, alone or in combination, on fermentation and microbial diversity during in vitro culture of bovine rumen microbes

Authors: CASTAÑEDA-CORREA, ALEJANDRO - Universidad Autonoma De Chihuahua; CORRAL-LUNA, AGUSTIN - Universidad Autonoma De Chihuahua; Hume, Michael; Anderson, Robin; RUIZ-BARRERA, OSCAR - Universidad Autonoma De Chihuahua; CASTILLO-CASTILLO, YAMICELA - Universidad Autonoma De Chihuahua; RODRIGUEZ-ALMEIDA, FELIPE - Universidad Autonoma De Chihuahua; SALINAS-CHAVIRA, JAIME - University Of Tamaulipas; ARZOLA-ALVAREZ, CLAUDIO - Universidad Autonoma De Chihuahua

Submitted to: Journal of Environmental Science and Health
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/5/2018
Publication Date: 11/15/2018
Citation: Castañeda-Correa, A., Corral-Luna, A., Hume, M.E., Anderson, R.C., Ruiz-Barrera, O., Castillo-Castillo, Y., Rodriguez-Almeida, F., Salinas-Chavira, J., Arzola-Alvarez, C. 2018. Effects of thymol and carvacrol, alone or in combination, on fermentation and microbial diversity during in vitro culture of bovine rumen microbes. Journal of Environmental Science and Health. 54(3):170-175. https://doi.org/10.1080/03601234.2018.1536580.
DOI: https://doi.org/10.1080/03601234.2018.1536580

Interpretive Summary: The plant-produced essential oils, thymol and carvacrol, are being investigated extensively by researchers worldwide as potential antibiotic-alternatives to kill pathogenic bacteria inhabiting the gut of food-producing animals. However, results from a number of studies have been inconsistent, with some showing beneficial effects and others showing negative effects on numbers of pathogenic bacteria as well as on beneficial bacteria important for optimal gut function. To determine if the inconsistent effects obtained in these earlier studies may be due to improper balance between the two essential oils, we conducted a study where we tested six different combinations of thymol and carvacrol in ratios of 100:00, 80:20, 60:40, 40:60, 20:80, and 00:100 in a commercial dose of (0.2 mg/mL) against populations of gut bacteria from a cow. We found that production of the bacterial end-product, methane, decreased more in the high carvacrol-containing treatments, and the gene profile of the total bacterial populations was more dramatically affected in the populations grown with the higher carvacrol-containing treatments. This suggests that treatments containing higher amounts of carvacrol were more potent against the microbial population than treatments containing higher amounts of thymol. Adverse effects of the treatments on digestibility of the dietary components were slight if at all. These results demonstrate that the potency of the two different essential oil components, thymol and carvacrol, are not equal and that the inconsistency observed in previous studies may be due to differences in the ratios of these two compounds. This research will ultimately help researchers develop better and more consistent dose formulations of these essential oils to help producers control pathogens in their animals.

Technical Abstract: Two essential oils (EO), thymol and carvacrol, were used in six ratio (100:00, 80:20, 60:40, 40:60, 20:80, and 00:100) combinations of both EO and in a dose of 0.2 g L**-1 in bovine ruminal culture medium, 24-h cultures, to evaluate effects on total gas production (TGP), methane production, in vitro dry matter digestibility (IVDMD), and in vitro culture population dynamics of methanogenic and total bacteria. Total DNA extracted from ruminal microorganisms was subjected to denaturing gradient gel electrophoresis (DGGE)-PCR to examine effects on bacterial populations. The effect of EO on TGP and IVDMD were assessed by comparison to untreated control cultures. In general, methane production by the microbial populations appeared to be higher with treatments containing the highest concentration of thymol than with treatments containing more carvacrol, resulting in a tendency for greater methane-inhibiting activity achieved as the thymol concentration in the thymol:carvacrol mixtures decreased linearly. The population of total bacteria with a 74.5% Dice similarity coefficient for comparison of DGGE band patterns indicating shifts in bacterial constituents as EO ratios changed. No effects on TGP or IVDMD, while only slight shifts in the methanogenic populations were seen with an overall 91.5% Dice similarity coefficient.