CONCLUSIONS
Gut microbiota played a protective role in the prevention of chicken colibacillosis and the pharmacological action of baicalin. The altered specific gut bacterial and/or metabolites may be served as indicators to predict the occurrence and prognosis of chicken colibacillosis. Our findings may provide a paradigm for the mechanistic studies of compounds and aid the exploration of the mechanisms and pathways underlying the function of herbal medicines.
Key words : Chicken colibacillosis, baicalin, gut microbiota, metabolites
Introduction
Chicken colibacillosis, a localized and systemic disease caused by avian Escherichia coli(APEC), causedhuge economic losses to the poultry industry and threatened food security, which is responsible for the use of very significant volumes of antibiotics in commercial poultry farming(Peek, Halkes, Tomassen, Mes, & Landman, 2013). Despite being known for over a century and studied for a long time, the pathogenesis of colibacillosis remains poorly understood. Up until now, it is widely accepted that the systemic form of colibacillosis from a respiratory origin that induces colisepticemia. Colonization of the trachea and air sacs is considered the first step of a systemic infection by APEC, followed by the colonization of the lung, liver and the pericardium(Guabiraba & Schouler, 2015). Therefore, we considered that targeting the respiratory infection stage of APEC and stopping the APEC from entering the blood circulation may be an effective way to prevent and cure colibacillosis.
The gut microbiota, consisting of mostly bacteria, plays a positive player in the host defence system, regulating mucosal immunity and systemic immunity(Noverr & Huffnagel, 2004; Trompette et al., 2014). Recent studies have reported that gut microbiota modulated the pulmonary immune during respiratory disease through what is often called “gut-lung axis”(Budden et al., 2017; Dumas, Bernard, Poquet, Lugo-Villarino, & Neyrolles, 2018). Many respiratory diseases occurred and developed accompanying with intestinal flora alteration(Dickson, Martinez, & Huffnagle, 2014). Moreover, the gut microbiota contributed the protection against pneumococcal pneumonia and Mycobacterium tuberculosis in lung(Dumas, Corral, et al., 2018; Schuijt et al., 2016). What role does gut microbiota play in chicken colibacillosis, however, remains elusive.
Scutellaria baicalensis , a Chinese traditional medicine, has been widely used to treat various diseases, such as influenza, pneumonia, dysentery, and cancer(Z. L. Wang et al., 2018). Baicalin, a naturally occurring constituent, was extracted from the dry roots of Scutellaria baicalensis and possessed anti-inflammatory, anti-allergic, anti-oxidant, hepatoprotective, and anti-tumor activities. In the previous study, we have found that baicalin had a protective effect against colibacillosis. However, the precise mechanism is still unclear. Recent report has manifested that metabolic activities of intestinal microflora may be of a great importance for herbal medicines to express the pharmacological effects(An et al., 2019). Myung-Ah Jung et.al, has proved that orally administered baicalin was metabolized to baicalein and oroxylin A by intestinal microbiota, which enhances its anti-inflammatory effect by inhibiting NF-κB activation(Jung, Jang, Hong, Hana, & Kim, 2012a). Furthermore, modern studies discovered that the administrated herbal medicines also interacted with gut microbiota and regulated the composition of the flora to improve the disease, such as diabetes mellitus(Creely et al., 2007). Hence, we speculated that gut microbiota played an important role in the process of baicalin exerting pharmacological effects. Similarly, baicalin may regulate the gut microbiota and its metabolite to protect chicken against colibacillosis.
Therefore, to understand the role of gut microbiota in the chicken colibacillosis and pharmacological effect of baicalin, as well as explore the protective mechanisms of baicalin on colibacillosis, we utilized APEC-O78 to establish the model of colibacillosis and applied the broad-spectrum antibiotic (Abx) to deplete the gut microbiota. Then, we measured the secretion of inflammatory cytokines, gene expression of inflammatory cytokines and tight junction, histopathological changes and viscera index. Furthermore, after orally administration of baicalin, we measure the alteration of gut microbiota and its metabolite by 16s rDNA sequencing and ultrahigh-performance liquid chromatography (LC-MS).