Objective: To observe the intestinal flora changes during the construction of antibiotic associated diarrhea(AAD) model and the effect of Lizhong Tang on intestinal flora changes in AAD model. Method: Eighty-one male BALB/c mice were selected forpreliminary experiment. High

medium and low dose (5

1

0.5 g·kg-1) ampicillin was used to construct intestinal flora disorder model

then the mice were fed with Clostridium difficile (1.6×108 CFU

colony-forming units) to construct the AAD model

and finally were treated with high

medium and low dose (7.5

5.5

3.5 g·kg-1) Lizhong Tang respectively. According to the animal phenotype and optimum treatment conditions during preliminary experiment

20 male BALB/c mice were selected and randomly divided into 4 groups (n=5 in each group):blank group

intestinal flora disorder group

AAD group

Lizhong Tang treatment group (7.5 g·kg-1). Modeling and treatment were conducted according to optimization steps. Fecal samples in four groups were respectively mixed as XL1

XL2

XL3

XL4

and then were subjected to flora changes analysis using 16 S rRNA high-throughput sequencing technology. Result: The phenotypic changes during AAD model building were consistent with clinical AAD symptom. The intestinal flora changes at OTUs level were 860

282

385

and 394

respectively;the abundance changes at phylum level were as follows:Proteobacteria (6.94%

41.77%

1.99%

2.89%)

Firmicutes (44.34%

34.89%

36.82%

32.11%)

Bacteroidetes (46.6%

22.74%

60.8%

64.49%) respectively;the number changes at genus level were 88

58

52

and 59 respectively. There were significant flora changesin all groups (P<0.05). Conclusion: The intestinal flora structures were changed drastically with decreased diversity and abundance during the construction of AAD model;Lizhong Tang could change the structure of intestinal flora in AAD model

and increase the diversity of flora.