Results
Protective effect of the gut microbiota during APEC-inducedchicken colibacillosis
To study the role the gut microbiota played in chicken colibacillosis,
we first applied the broad-spectrum antibiotic (Abx) to deplete the gut
microbiota. Administration of Abx resulted in a considerable reduction
of richness (Fig. 1A) and diversity (Fig. 1B) of gut microbiota in
chickens. Furthermore, principle coordinate analysis (PCoA) plot based
on Unweighted Unifrac revealed that there was clear separation of
clusters between control group compared with Abx-treated group chicken
(Fig. 1C). In addition, Venn diagrams showing numbers of genera in
Abx-treated group were significantly reduced (Fig. 1D). These results
suggested that treatment of Abx significantly changes the structure of
gut microbiota, and reduced the gut microbiota diversity and richness in
chicken.
Furthermore, chicken from control and gut microbiota-depleted groups
were intranasally challenged with APEC to induce the model of
colibacillosis. Infection of APEC results in severe pathological injury
of lung (Fig. 2A), and colon, heart, liver, and spleen (see
supplementary fig. S1A), increased the production of proinflammatory
cytokines TNF-α, IL-1β, and IL-6 both at gene and protein levels (Fig.
2B-D and supplementary Fig. S1B-D), as well as increased the bacterial
outgrowth in the lung (Fig. 1E). In addition, infection of APEC also
increased the viscera index of lung, heart, liver, spleen, and kidney
(see supplementary Table S1). However, these inflammatory injuries
induced by APEC were more pronounced in gut microbiota-depleted chicken
when compared to the infected with control chicken (Fig. 2A-E and
supplementary Fig. S1A-D and Table S1). Moreover, the concentration of
total proteins in bronchoalveolar lavage fluid (BALF) and the expression
of tight junction protein of lung tissues were measured to evaluate
pulmonary air-blood barrier permeability. Infection of APEC increased
the levels of total protein in BALF, and the levels of total protein
were higher in
Abx+APEC
group than APEC group (Fig. 2F). In addition, the expression of junction
protein of air-blood barrier, including occludin, claudin-3, and ZO-1
were significantly reduced after infected with APEC, and these changes
are more obviously in gut Abx+APEC group (Fig. 2G-I). There results
suggested that depletion of gut microbiota increase the severity of
colibacillosis and increased the permeability of air-blood barrier
induced by APEC.