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Exploring Quorum Sensing to optimize phytogenic feed additives

By Tim Goossens, PhD, Nutriad International

Gut health is one of several factors important to obtaining optimum efficiency and profitability in livestock production and there is increasing evidence of the central role played by gut microbiota in animal health and disease. Many feed additives are therefore designed to specifically support gut health. Numerous phytochemicals, supplemented as dried herbs, plant

extracts or essential oils, have been described to have favourable effects on myriad parameters, such as digestion, blood pressure, anti-inflammation and hepatic protection. It is therefore a challenge to rationally develop a botanical feed additive mixture: how does one select ingredients from a plethora of plant-derived components, each triggering several physiological responses, with the objective of supporting animal health and performance as much as possible?

Gut microbiota Several phytogenic feed additives that aim to support gut health and performance in livestock animals are therefore trying to target the composition and activity of the gut microbiota. This can be explained by the fact that, in recent years, evidence has been accumulating for a pivotal role of the gut microbiota in maintaining the health status of several organs and tissues, including the digestive tract. While in the past, the intestinal microbial composition was considered to mainly reflect the health status of humans and animals, it is becoming ever more clear that this bacterial community can directly and indirectly affect the development and function of several tissues and organs, including the enterocytes, the gut-associated lymphoid tissue, the liver and the brain (Gareau et al., 2010). When selecting for ingredients affecting gut bacteria, such as

botanical components, many feed additive producers rely on in vitro experiments that demonstrate their bacteriostatic effect. However, the active ingredients of these botanicals will end up in the digestive tract of production animals at concentrations far below the minimal concentration needed to inhibit growth of (pathogenic) bacteria. It might therefore be a more reliable approach to select feed additive ingredients by focusing on the effects botanical components can have at much lower concentrations, and that are likely to be of relevance for controlling bacterial activity in vivo and improving gut health.

Quorum Sensing One of the potential mechanisms of botanical feed additives that can be placed in the picture is their effect on quorum sensing (QS). Bacteria continuously secrete QS signals, which allows them to synchronize their behaviour. More specifically, when the number (the quorum) of a certain bacterial species or group in an environment increases, so will


the concentration of their secreted QS signals (Figure 1). If a specific threshold of these molecules is reached, it will activate QS-dependent signalling pathways inside the bacteria, resulting in biochemical responses that are often associated with pathogenicity, such as the production of toxins.

Figure 1: Bacteria continuously produce and secrete QS signals in the environment, as depicted by concentric circles around bacteria in this figure. If the concentration of a bacterial species is low (as shown on the left), the QS signals will get rapidly diluted in the environment. On the contrary, if the number of bacteria increases (on the right), so will the concentration of QS signal molecules in the environment. If a certain threshold of these molecules is reached, QS signaling will become activated inside the bacteria (shown as a lightning bolt).

As a consequence, compounds able to disrupt QS are being

increasingly investigated in human medical research as potential alternatives to antibiotics due to their efficacy at low concentrations and the low chance of bacteria developing resistance against these non-lethal molecules (Figure 2).

Figure 2: Number of articles referring to “quorum sensing”, as listed in the PubMed database ( Bars represent the (non-cumulative) number of QS articles that have been included per year in the period 1994-2015.

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