Impact of a blend of four <i>Alkalihalobacillus clausii</i> strains (O/C, N/R, SIN, and T) on gut barrier integrity and immune modulation with PPIs: an <i>in vitro</i> SHIME study

Alkalihalobacillus clausii is effective in alleviating PPI-induced dysbiosis; however, its effects on gut barrier function and inflammation remain unclear. This study explored A. clausii (O/C, N/R, SIN, and T) effects on gut barrier function during PPI-induced dysbiosis using Triple-M-SHIME® model. Reactors were supplemented with PPI alone (PPI control); simultaneous PPI + A. clausii (preventive); and PPI for 2 weeks followed by A. clausii (curative). Caco-2/THP1-Blue™ co-cultures were exposed to colonic SHIME® suspensions for 24 h for TEER measurement, followed by lipopolysaccharide stimulation for measurement of cytokine secretion and NF-κB. Preventive treatment did not improve inflammation-induced barrier disruption, but was slightly improved with curative treatment, particularly in the distal colon. Colonic ferments following A. clausii supplementation increased IL-10 secretion and pro-inflammatory signals in the ileum. In the proximal and distal colon, PPI treatment reduced pro-inflammatory markers during and after treatment, while increasing anti-inflammatory cytokines following prolonged incubation. Preventive treatment with A. clausii, reduced pro-inflammatory markers and IL-10, while increasing IL-6 secretion. Curative A. clausii treatment lowered pro-inflammatory markers. Enhanced colonic fermentation by A. clausii thus showed potential in improving gut barrier function and modulating inflammation with complex colon region-specific responses, particularly with curative treatment.