Gut dysbiosis and small intestinal bacterial overgrowth as independent forms of gut microbiota disorders in cirrhosis

BACKGROUND: Gut dysbiosis and small intestinal bacterial overgrowth (SIBO) are commonly observed in patients with cirrhosis. Despite the substantial number of articles describing the relations between disorders of gut microbiota and various manifestations of cirrhosis, dysbiosis and SIBO were always studied separately. AIM: To study the relationship of gut dysbiosis and SIBO in cirrhosis. METHODS: This observational study included 47 in-patients with cirrhosis. Stool microbiome was assessed using 16S rRNA gene sequencing. SIBO was assessed using the lactulose hydrogen breath test. RESULTS: SIBO was found in 24/47 (51.1%) patients. Patients with SIBO had a higher abundance of Firmicutes (P = 0.017) and Fusobacteria (P = 0.011), and a lower abundance of Bacteroidetes (P = 0.013) than patients without SIBO. This increase in the abundance of Firmicutes occurred mainly due to an increase in the abundance of bacteria from the genus Blautia (P = 0.020) of the Lachnospiraceae family (P = 0.047), while the abundance of other major families of this phylum [Ruminococcaceae (P = 0.856), Peptostreptococcaceae (P = 0.066), Clostridiaceae (P = 0.463), Eubacteriaceae (P = 0.463), Lactobacillaceae (P = 0.413), and Veillonellaceae (P = 0.632)] did not differ significantly between the patients with and without SIBO. Reduced level of Bacteroidetes in samples from patients with SIBO was a result of the decrease in bacterial numbers from all the major families of this phylum [Bacteroidaceae (P = 0.014), Porphyromonadaceae (P = 0.002), and Rikenellaceae (P = 0.047)], with the exception of Prevotellaceae (P = 0.941). There were no significant differences in the abundance of taxa that were the main biomarkers of cirrhosis-associated gut dysbiosis [Proteobacteria (P = 0.790), Bacilli (P = 0.573), Enterobacteriaceae (P = 0.632), Streptococcaceae (P = 0.170), Staphylococcaceae (P = 0.450), and Enterococcaceae (P = 0.873)] between patients with and without SIBO. CONCLUSION: Despite the differences observed in the gut microbiome between patients with and without SIBO, gut dysbiosis and SIBO are most likely independent disorders of gut microbiota in cirrhosis.