Potential and challenges of tannins as an alternative to in-feed antibiotics for farm animal production

Huang, Qianqian; Liu, Xiuli; Zhao, Guoqi; Hu, Tianming; Wang, Yuxi

One of the reasons that medicinal plants and herbs have been used for a long history without concern of antimicrobial resistance is probably that multiple compounds presented in the formula or complex prescription act synergistically. Such synergisms among individual compounds in complex and dynamic mixtures make microorganism difficult to adapt to the multiple compounds. However, this may not be the case in prolonged use of the isolated single plant-based antimicrobial compound, which may result in the development of resistance in some microorganisms. A good example is antimalarial compound, artemisinin, in traditional Chinese medicinal plant Qinghao (Artemisia annua L, Asteraceae). Qinghao as a medicinal herb has been used to effectively treat malaria for a long history in Chinese medicine (Miller and Su, 2011) . However, the reduction of the effectiveness of the purified form of artemisinin against malaria after using for several decades indicates that the microorganism have developed some sort of resistance to this compound. This trend is similar to the development of antibiotics resistance of bacteria. This suggests that prolonged use of plant compounds in their purified forms as antimicrobial growth promoter in animal feed has the risk to develop antimicrobial resistance. The majority of the tannins used presently in animal industry are either crude extract of mixtures of different molecular sizes or whole plant with a whole array of secondary compounds. This, coupled with the variations in chemical compositions and structures of the compounds from different sources and growing conditions, would reduce the likelihood of forming resistance by microorganisms to the complex tannins. However, little research has been done in this area and regulatory agent, scientific community and production industry need to make joint efforts to prevent microorganisms from forming resistance to tannins and other plant secondary compounds that are important to human health as this will have huge implication to humankind.