Gram-Negative Bacterial Overgrowth Predominated by: Potential Association with Intestinal Barrier Impairment and Inflammatory Diarrhea in Cats

Background: Feline diarrhea is one of the most common gastrointestinal disorders encountered in veterinary clinics. Dysbiosis of Gram-negative bacteria is widely presumed to be a key cause of this disease, yet adequate in vivo evidence demonstrating its roles in provoking inflammation and impairing intestinal barrier integrity is still lacking. In this study, we investigated the effects of bacterial flora in cats with diarrhea on gut health in mice. Results: The results show the following: (1) Microorganisms in feces of diarrheal cats can cause weight loss in antibiotic-treated mice; the histopathological section of the colon showed that neutrophil aggregation occurred in the colon of mice in the fecal bacteria transplantation group; this indicates that gavage using fecal microbes from diarrheic cats could impair intestinal barrier integrity in antibiotic-treated recipient mice. (2) In addition, microbes in cats with diarrhea can induce inflammation in the colon and aggregation of macrophages, which may be caused by some Gram-negative bacteria in feces of cats with diarrhea. (3) The composition of the intestinal microbial community was analyzed by 16S rRNA gene sequencing, and it was found that the relative abundance of Escherichia–Shigella in feces of cats with diarrhea was significantly higher than that of normal cats. (4) Quantitative analysis of fecal samples revealed that diarrheic cats exhibited a significantly higher load of fecal Gram-negative bacteria compared with healthy cats, verifying that excessive colonization of Gram-negative bacteria may be highly correlated with feline diarrhea. Conclusion: In summary, fecal microbes from diarrheic cats are capable of triggering intestinal inflammation and barrier damage in antibiotic-treated mice. Excessive proliferation of Gram-negative bacteria, mainly Escherichia–Shigella species, may be highly associated with feline diarrhea.