Abstract: Objective To evaluate the effect of water pollution with dexamethasone on intestinal flora in mice. Methods Twenty
Balb/c mice were randomly divided into control group and low-, moderate- and high-dose dexamethasone groups. The mice
in dexamethasone groups were exposed to dexamethasone sodium phosphate in drinking water at doses of 0.035, 0.225, and
2.25 ng for 36 days. The changes in behaviors, fur condition, and feces of the mice were observed daily. All the mice were
sacrificed at 36 days and the tissues in the ileocecal region was collected for denaturant gradient gel electrophoresis (DGGE) of
16S rDNA V6 variable regions of microbes and sequence analysis with BLAST. Results The mice in the 3 dexamethasone
groups all showed aggressive behaviors. Cluster analysis of DGGE graph showed relatively stable floras in the ileocecal region
in all the mice, but principal component analysis identified differences in the dominating flora among the groups. Diversity
analysis of the flora revealed significantly increased amount and types of bacteria in the intestinal flora in all the 3
dexamethasone groups (P<0.05 or 0.01) compared with the control group. Sequence analysis of 16S rDNA V6 regions showed
15 common bacterial species and 2 differential species between the dexamethasone groups and the control group with changes
in the type and proportion of the dominating bacterium in the dexamethasone groups. Lactobacillus colonization was detected
in the control group but not in moderate- and high-dose dexamethasone groups, and Shigella species were found in the latter
two groups. Conclusion Water contamination with dexamethasone can affect the nervous system of mice, cause changes in the
types and amounts of intestinal bacteria and the dominating bacteria, and inhibit the colonization of probiotics in the intestinal
floras to increase the risk of invasion by intestinal pathogenic bacteria.