Antidiarrheal Activity of Fermented Soybean Powder by Bacillus subtilis DKU_09 Strain in Mice with Castor Oil-Induced Diarrhea

Diarrhea is characterized by excessive intestinal secretion and motility, often linked to inflammatory activation. Although synthetic antidiarrheal drugs are effective, their prolonged use can cause side effects, underscoring the need for safe, natural alternatives.

This study investigated the antidiarrheal and anti-inflammatory activities of Bacillus subtilis DKU_09-fermented soybean (FS) powder in a mouse model of castor oil-induced diarrhea.

Male ICR mice were orally administered FS (100, 200, or 300 mg/kg) for 7 days before the induction of diarrhea with castor oil. Diarrheal onset, frequency, fecal water content, and gastrointestinal (GI) transit were recorded. Inflammatory mediators in the small intestine were analyzed using real-time polymerase chain reaction and Western blotting, while serum immunoglobulin A (IgA) and immunoglobulin G (IgG) were measured by enzyme-linked immunosorbent assay.

Pretreatment with FS significantly delayed the onset of diarrhea (FS200: 132.0 ± 9.8 min vs. castor oil-treated control [DC]: 76.9 ± 5.6 min, P < .05) and reduced diarrheal frequency (FS200: 32.9 ± 5.4% vs. DC: 51.9 ± 6.1%, P < .05). FS normalized the accelerated GI transit and markedly suppressed intestinal inflammation. The expression of Il-1β , Cox-2 , mPGES-1 , and NF-κB ( p65 ) mRNA was significantly decreased by FS, accompanied by inhibition of mitogen-activated protein kinase (MAPK) phosphorylation (ERK, JNK, and p38). Serum IgG and IgA levels were unaffected, indicating that the effects were localized to intestinal tissue.

Soybeans fermented by B. subtilis DKU_09 exert potent antidiarrheal effects through suppression of the NF-κB/Cox-2/PGE ₂ and MAPK signaling pathways, thereby reducing intestinal inflammation and motility. These findings suggest that the FS used in the present study may serve as a safe and natural functional food for the management of acute diarrhea.