Synbiotic Therapy Reduces the Pathological Gram-Negative Rods Caused by an Increased Acetic Acid Concentration in the Gut

The mechanisms for the improvement of the gut flora and the intestinal environment by synbiotic therapy are unclear. This study evaluated the changes in the gut flora and the intestinal environment after synbiotic therapy, and tried to clarify the mechanisms by which synbiotic therapy reduces pathological bacteria in the gut. A total of 47 enteral feeding patients with long-term mechanical ventilation support were enrolled in the study. Patients were randomly assigned to synbiotic and control groups, at a two to one ratio. Patients in the synbiotic group were administrated Lactobacillus, Bifidobacterium, and galactooligosaccharides as synbiotics for 8 weeks. The characteristics of the patients were not significantly different between the control (n = 16) and synbiotic (n = 31) groups. In the synbiotic group, the counts of Bifidobacterium and Lactobacillus in the gut increased significantly to 100 times the initial level following synbiotic treatment. The acetic acid concentration increased (71.1 +/- A 15.9 vs. 46.8 +/- A 24.1 mu mol/g) and pH decreased in the gut in comparison with the control group. The concentration of acetic acid in the gut increased in proportion to the Bifidobacterium counts. The counts of pathological gram-negative rod decreased significantly to one-tenth of the initial level in inverse proportion to the Bifidobacterium counts. Furthermore, the amount of Pseudomonas aeruginosa in the lower respiratory tract decreased significantly after synbiotic therapy compared to the controls. Synbiotic therapy reduces the pathological Gram-negative rods by increasing the acetic acid concentration in association with an increased counts of Bifidobacterium.