Influence of symbiotic administration on gut microbiota: an exploratory study at different levels and intensity of spinal cord injury

Aim: Spinal cord injury (SCI) disrupts autonomic regulation of the gastrointestinal tract, resulting in altered motility, microbial dysbiosis, and decreased production of short-chain fatty acids such as butyrate, a metabolite with neuroprotective properties. This study aimed to evaluate the effects of SCI level and severity on gut microbiota composition and butyrate concentration, and to determine the impact of symbiotic supplementation with Enterococcus faecium and agave inulin on microbial and metabolic recovery. Methods: Twenty female Sprague Dawley rats were randomized into five groups: Sham, thoracic five moderate (T5M), thoracic five severe (T5S), thoracic nine moderate (T9M), and thoracic nine severe (T9S). Fecal samples were collected four weeks post-injury and again after four weeks of daily symbiotic administration. Butyrate levels were quantified by gas chromatography, and microbial composition was analyzed by 16S ribosomal RNA (16S rRNA) sequencing (V3–V4 region). Locomotor recovery was assessed weekly using the Basso, Beattie, and Bresnahan (BBB) scale. Results: All SCI groups displayed significant dysbiosis compared with Sham, characterized by decreased relative abundance of butyrate-producing genera such as Clostridium at week four, as confirmed in the main dataset. Following symbiotic supplementation, Bifidobacterium, Lactobacillus, and Clostridium levels showed partial restoration, although responses varied by injury site and severity. The T9M group demonstrated the most consistent recovery of butyrate-producing taxa; however, butyrate concentration decreased after treatment, while T9S showed a significant increase in butyrate concentration, and T5S exhibited minimal change. Motor recovery was greatest in T9M, followed by T9S and T5M, with no significant improvement in T5S. Conclusions: SCI level and severity strongly influenced microbial dysbiosis, butyrate metabolism, and motor recovery. Symbiotic supplementation partially restored butyrate-producing bacterial taxa, with the most pronounced metabolic and functional benefits observed in the T9M group. These findings support a level-dependent role of gut-brain axis modulation as a potential therapeutic strategy after SCI.