Fig. 3.

An expansion of Proteobacteria is a microbial signature of dysbiosis in the fecal microbiota. The fecal microbiota of healthy individuals is dominated by obligate anaerobic bacteria belonging to the phyla Firmicutes and Bacteroidetes (30). A dysbiotic expansion in the fecal microbiota of facultative anaerobic bacteria of the phylum Proteobacteria is observed in patients with necrotizing enterocolitis (50), irritable bowel syndrome (12, 33), inflammatory bowel disease (18), colorectal cancer (3), or in individuals consuming a high-fat diet (46), with chronic alcohol usage (15), or undergoing inflammaging (48). A dysbiotic expansion of Proteobacteria in the large intestine is also observed in mouse models of chemically induced colitis (43), genetically induced colitis (23), antibiotic treatment (6, 59), and infection with Salmonella enterica (68), Citrobacter rodentium (43), or Toxoplasma gondii (27).