Bacillus clausii Attenuates 5-Fluorouracil-Induced Intestinal Mucositis in Mice

5-Fluorouracil (5-FU) is an antimetabolite widely prescribed in cancer treatments, but its use in highly proliferative tissues can cause significant problems such as mucositis. <i>Bacillus clausii</i> is a probiotic commonly used for protection against acute diarrhea, gastrointestinal dysbiosis and inflammatory bowel diseases. We investigated the effect of <i>B. clausii</i> on 5-FU intestinal mucositis in mice. <i>B. clausii</i> was administered concomitantly with 5-FU on the first day and alone for the other two days. After the third day of 5-FU (450 mg/kg, ip), the animals were euthanized. Ileum samples were removed for evaluation for histopathological and biochemical analyses (myeloperoxidase (MPO), glutathione (GSH), malondialdehyde (MDA), catalase (CAT), interleukin-1 beta (IL-1β) and tumor necrosis factor alpha (TNF-α). In addition, we investigated gastric emptying and intestinal transit, intestinal permeability, intestinal smooth muscle contractility, transepithelial electrical resistance and intestinal transport of water and electrolytes. <i>B. clausii</i> reduced histopathological scores and increased the villus/crypt ratio in all intestinal segments after mucositis. <i>B. clausii</i> attenuated 5-FU-induced weight loss. The probiotic treatment increased GSH levels, reduced MPO and CAT activity, and also reduced MDA, IL-1β and TNF-α levels. <i>B. clausii</i> attenuated the delay in gastric emptying, water and electrolyte secretion and intestinal hypercontractility, and increased 5-FU-induced intestinal permeability. Thus, our data suggest that <i>B. clausii</i> may be a potential candidate for the treatment of chemotherapy-induced intestinal mucositis.