Bacillus safensis NMCC-189 attenuates chronic restraint stress-induced depressive phenotypes and modulates neurochemical and gene expression changes in mice.

The microbiota-gut-brain axis has been associated with depression, and probiotics are considered potential modulators of stress-related neurobiological processes. This study compared the effects of Bacillus safensis NMCC-189, administered alone or in combination with fluoxetine, in a murine model of chronic restraint stress. The animals were euthanised at predetermined intervals (days 7, 14, and 21; n = 5 per group) for biochemical, and molecular analyses after undergoing behavioural assessments for 21 days. Restraint stress significantly increased immobility time in the tail suspension test (p < 0.001) and induced behavioural, biochemical and neurochemical disturbances as compared to normal control (p < 0.001). Treatment with B. safensis and fluoxetine improved behavioural outcomes, while the combination group showed significant overall improvement (p < 0.001). Stress-elevated cortisol levels were reduced in the combination group (90 ± 3.54, p < 0.001). Likewise, the oxidative stress marker, MDA, was significantly lower in the combination group (74.03 ± 4.01, p < 0.001). Under stress conditions, neurotransmitter levels such as serotonin were increased in the combination group (0.59 ± 0.12, p < 0.001) compared with stressed controls and individual treatments. Gene expression analysis revealed significant modulation of neuroplasticity-related genes (p < 0.001), although these findings reflect transcriptional changes rather than direct activation of functional pathways. Overall, Bacillus safensis NMCC-189 was associated with improvements in stress-induced behavioural and molecular alterations, while combination treatment generally showed greater effects across several biochemical and neurochemical parameters. These findings provide preliminary preclinical evidence and warrant further studies to confirm the underlying mechanisms and clinical relevance.