Serious intestinal pro-inflammatory responses are generally associated with the impairment of the intestinal barrier.32 Compared with mice gavaged with healthy salivary microbiota, periodontitis-related salivary microbiota significantly reduced the expressions of tight junction-related proteins ZO-1 and occludin (Figure 5a–c), which play an essential part in maintaining the intestinal barrier. This evidence concerns the gene OCLN and periodontitis.