Microbial ecology of the murine gut associated with the development of dextran sodium sulfate-induced colitis

Abstract

Background: Dextran sodium sulfate (DSS) is used to induce murine colitis. Although the exact mechanism by which DSS administration causes disease is unknown, evidence suggests that the resident bacteria play a role in the development of murine DSS colitis, analogous to their role in human inflammatory bowel diseases.

Methods: C57BL/6 mice received 5% DSS in the drinking water and were euthanized 3 days and 14 days after the initiation of DSS treatment. Culture-independent methods were used to follow changes in the community structure of the gut's microbiota following DSS treatment. Histologic evidence of disease and changes in host gene expression were assessed.

Results: Histologic colitis was minimal in DSS-treated animals at 3 days, but severe after 14 days. Analysis of 16S rRNA-encoding gene clone libraries demonstrated that the microbial communities in the ceca of DSS-treated mice were distinct from those in control mice. The microbiota in the cecum of DSS-treated animals was characterized by an overall decrease in microbial richness, an increase in members of the phylum Verrucomicrobia, and decrease in Tenericutes. Changes in the host's inflammatory response and microbial communities occurred before the histologic appearance of severe disease in the colon, but were seen concurrently in the cecum.

Conclusions: DSS administration is associated with reproducible changes in the gut microbial diversity of mice. Microbial and immunological changes appeared before the development of severe inflammation in the colon. This indicates that these changes in microbial community may play role in the potentiation of the abnormal inflammatory response seen in DSS-treated animals.

Figure 1

Histopathology in DSS-treated mice. Hemotoxylin and eosin (H&E) stained sections were prepared from the cecum of (a) untreated control mice (b) mice after 3 days of DSS treatment and (c) after 14 days of DSS. Arrow indicates submucosl edema. H&E sections were also prepared from colon samples of (d) untreated controls (e) mice after 3 days of DSS treatment (arrow points to inflammation) and (f) animals after 14 days of DSS (arrow shows abscess). Histopathologic scores were calculated for sections from all 31 animals for (g) cecum and (h) colon sections. Statistical analysis done was Kruskal-Wallis test. *p< 0.05 **p<0.001. Initial magnification 40X

Figure 2

Changes in host gene expression after 3-days (dark bars) or 14-days (grey bars) ± standard deviation of DSS administration. Expression levels were compared to expression in tissue from animals not exposed to DSS. Statistical analysis done was Student’s t-test. Statistically significant differences (p<0.05) are denoted by asterisks (*).

Figure 3

Comparison of the cecal community in control animals (black triangles) and in animals following 3 days of DSS treatment (white squares) and 14 days of treatment (black squares). Using an OTU definition of 97% similarity, the Bray-Curtis similarity metric was calculated for each pair-wise comparison and then the results displayed in denrogram format. Analysis by the parsimony test indicates that there is a statistically significant (*p<0.001) difference between the communities in control animals and in both groups of DSS-treated animals.

Figure 4

Changes in the cecal gut microbial community following DSS administration (A) at the phylum level (B) within the phylum Firmicutes. Analysis was done by ANOVA and statistical significance (p<0.05) is denoted by asterisks (*).