Effects of Achyranthes bidentata Polysaccharides on Intestinal Morphology, Immune Response, and Gut Microbiome in Yellow Broiler Chickens Challenged with Escherichia coli K88

Abstract

The present study was conducted to investigate the effects of dietary Achyranthes bidentata polysaccharide (ABPS) supplementation on performance, immune response, intestinal mucosal morphology, and gut microbiome in yellow-feathered broilers challenged with Escherichia coli K88. A 2 × 2 factorial design was used for the trial. Two hundred and forty one-day-old female broilers were randomly assigned to four treatments: (1) negative-control broilers were fed by a basal diet and saline (NG); (2) positive-control broilers were fed by a basal diet and orally challenged with 10⁸ CFU E. coli K88 (CNG); (3) ABP group broilers were fed by a basal diet containing ABPS (500 mg/kg of feed) and saline; (4) CABP group broilers were fed by a basal diet containing ABPS (500 mg/kg of feed) and orally challenged with 10⁸ CFU E. coli K88. Growth performance, serum biochemical indexes, immune responses, intestinal mucosal morphology, and cecal microbial community structure were evaluated. The ABP group had greatest body weight (BW), average daily body weight gain (ADG), and intestinal villus height compared to other treatments (p < 0.05). The CABP group had a higher villus height/crypt depth ratio (V/C) compared with other treatments (p < 0.05). The expression levels of NF-κB were lower in the ABP group. The CNG group had higher Escherichia coli and Enterococcus contents in cecal samples compared to other treatments (p < 0.05). Serum glucose, uric acid, TNF-α, and Secretory Immunoglobulin A (S-IgA) levels were higher in broilers challenged with E. coli (p < 0.001) than that with saline. Broilers challenged with E. coli had reduced taxa richness in the cecal samples. Sequencing of 16S rRNA genes in cecal samples revealed that a lower proportion of Firmicutes and a higher proportion of Proteobacteria were detected in the broilers challenged with E. coli. Compared with the controls, dietary ABPS supplementation increased serum total protein, albumin, and S-IgA levels, but decreased serum glucose, uric acid, and TNF-α levels in broilers (p < 0.05). Diet supplemented with ABPS increased the Firmicutes/Bacteroidetes ratio and the abundance of Ruminococcaceae and Lachnospiraceae, and altered cecal microbiota community structure. These results suggest that ABPS can promote growth performance and improve intestinal morphology and microbiota community structure in broilers challenged with E. coli K88.

Keywords: Achyranthes bidentata polysaccharides; Escherichia coli K88; cecal microbiota; immune response; intestinal mucosal morphology.

Figure 1

Effects of ABPS and E. coli challenge on mucosal cytokines and S-IgA in yellow-feathered broilers. (A) Concentration of IL-4 in jejunal mucosa; the interaction effect between E. coli challenge and ABPS was observed for IL-4 throughout the trial period. (B) Concentrations of TNF-α and S-IgA in jejunal mucosa; ABPS and E. coli treatments were significant (p < 0.05) for TNF-α and S-IgA. Values are means ± SE, n = 6. Different superscripted lowercase letters within each group mean the values differ significantly (p < 0.05). NG: basal diet; ABP: supplemented with 500 mg ABPS additive per kg of diet; CNG: basal diet group with E. coli challenge; CABP: ABP group with E. coli challenge.

Figure 2

Response of NF-κB and EKR1/2 in the jejunum. (A) NF-κB and EKR1/2 immunostaining of mucosa (original magnification 100× and 400×). Only brown-colored staining was considered positive. (B) Density quantification of brown-colored staining. Significant interaction between E. coli challenge and ABPS was observed for NF-κB activation, but not for ERK1/2 activation (p = 0.055). Values are means ± SE, n = 6. Different superscripted lowercase letters within each group mean the values differ significantly (p < 0.05). NG: basal diet; ABP: supplemented with 500 mg ABPS additive per kg of diet; CNG: basal diet group with E. coli challenge; CABP: ABP group with E. coli challenge.

Figure 3

Effects of ABPS and E. coli challenge on intestinal mucosal morphology. (A) Intestinal (a: Duodenum; b: Jejunum; c: Ileum) mucosal morphology of 28-day-old yellow-feathered broilers was observed (40×). (B) The villi lengths, crypt depth, and the ratio of the villus length and crypt depth (V/C) were determined in intestinal samples. Values are means ± SE, n = 6. Different superscripted lowercase letters within each group mean the values differ significantly (p < 0.05). NG: basal diet; ABP: supplemented with 500 mg ABPS additive per kg of diet; CNG: basal diet group with E. coli challenge; CABP: ABP group with E. coli challenge.

Figure 4

Effect of ABPS and E. coli challenge on the cecal microbiota. (A) Cecal taxa richness assessed by α-diversity analyses using the chao1 method. (B) Cecal microbial community β-diversity (unweighted Unifrac, p > 0.05), which was demonstrated using principal coordinate analysis (PCoA) of the unweighted Unifrac distance matrices. Microbial communities were clustered according to challenge (E. coli-challenged vs. saline); however, there was no obvious clustering according to diet supplementation (ABPS vs. non-ABPS). The first two principal coordinates (PC1 and PC3) are plotted for each bird. The percentage of dataset variability explained by each principal coordinate is shown in the axes’ titles. Each dot represents one bird and each group is denoted by a different color (green, NG; orange, CNG; blue, CABP; red, ABP). (C) Microbiota taxa composition at the phylum levels is shown, labeled according to phyla (p) where available E. coli was significant (p < 0.05), and more description is provided in the results section. (D) The Firmicutes/Bacteroidetes ratio is shown. For the ABPS and E. coli treatment, this was significant (p < 0.05), and more description is provided in the results section. NG: basal diet; ABP: supplemented with 500 mg ABPS additive per kg of diet; CNG: basal diet group with E. coli challenge; CABP: ABP group with E. coli challenge.