Objective: This study is to investigate the effects of dexamethasone-contaminated water on the mouse growth and intestinal microflora composition. Methods: Totally 20 Balb/c mice were divided into the control group, and the low-, medium-, and high-dose groups. Animal body weight was recorded, and the animal appearance and behavior were observed, after treatment. After animal sacrifice, organ weight analysis was performed. Intestinal microflora composition was analyzed with denaturing gradient

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... l electrophoresis (DGGE) and 16S rDNA V6 se-quencing. Results: Messy fur and hostile behavior were observed in mice in the experimental groups. Compared with the control group (28.88±1.46 g), the mouse body weights in the low-, medium-, and high-dose groups (24.00±1.08, 26.17±1.76, and 25.43±0.95 g, respectively) were significantly declined (P<0.05). Moreover, for the experimental groups, the liver coefficient and spleen coefficient were significantly elevated (P<0.05), compared with the control group. DGGE profiling indicated stable intestinal microflora composition in mice. Principal component analysis (PCA) showed significant differences in the dominant microflora between the control and experimental groups. Microflora diversity analysis showed that, compared with the control group, the intestinal microflora amount (H'=3.74±0.0006368, 3.80±0.01153, and 3.84±0.00831, respectively and species (S=15.61±0.548, 16.43±1.095, and 16.82±0.548, respectively) were significantly increased in the experimental groups (P<0.05), compared with the control group (H'=3.65±0.01096 and S=14.41±1.517). The 16S rDNA V6 sequencing revealed totally 17 species of intestinal microflora, 15 of which were detected in all the groups. For the other 2 species, Lactobacillus bacteria existed only in the control group, while Shigellabacteria were observed only in the medium-and high-dose groups. Conclusion: Dexamethasone-contaminated water reduces the mouse growth, and alters the intestinal microflora composition. Dexamethasone contamination increases the microflora diversity and inhibits the probiotic colonization, facilitating the invasion of pathogenic bacteria.