A microbial ecosystem in which bacteria no longer live in a mutualistic association is called dysbiotic.
Generally, in a dysbiotic ecosystem, potentially pathogenic microbes take over at the expense of potentially beneficial microbes.
Dysbiosis is characterised by bacterial overgrowth in the small intestine due to reduced gastric acid production with excess bacterial fermentative activity. People with dysbiosis often have gluten or carbohydrate intolerance and their health deteriorates with the consumption of carbohydrates.
Deficiency dysbiosis is a condition characterised by an overall reduction in beneficial bacterial species (such as lactobacilli and/or bifidobacteria), which may occur as a result of unhealthy diets or antibiotic treatments, and may be associated with food intolerances, as a result of digestive enzyme deficiency (milk or meat intolerance).
Putrefactive dysbiosis, characterised by an increase in putrefactive bacteria (mainly Bacteroides), usually results from a diet high in fat and meat and low in fibre, the metabolisation of which can lead to products such as ammonia, amines and phenols, which could cause symptoms not limited to the gastrointestinal tract but can also affect the whole body.
Fermentative dysbiosis often affects patients with irritable bowel syndrome, patients receiving antibiotic treatment and those who reduce their carbohydrate intake (low fermentable oligosaccharide, disaccharide, monosaccharide and polyol (FODMAP) diet). Susceptibility dysbiosis is associated with a loss of tolerance of the gut microbiota in which genetic causes (leading to abnormal immune responses to components of the gut microbiota) play an important role and are linked to IBD and other similar diseases.
In susceptibility dysbiosis, alterations in the gut microbiota ecosystem are characterised by a reduced amount of probiotic bacteria, an increase in potentially pathogenic microbes (pathobionts), impaired gut motility and gut inflammation.
Fungal dysbiosis, characterised by the overgrowth of Candida or other fungal species in the gut microbiota, is favoured by a diet high in sugar and low in fibre.
Credit: Gagliardi A, Totino V, Cacciotti F, Iebba V, Neroni B, Bonfiglio G, Trancassini M, Passariello C, Pantanella F, Schippa S. Rebuilding the Gut Microbiota Ecosystem. Int J Environ Res Public Health. 2018 Aug 7;15(8):1679. doi: 10.3390/ijerph15081679. PMID: 30087270; PMCID: PMC6121872.