Research of human microbiota show that human gut is mainly inhabited by two phyla of bacteria – Firmicutes and Bacteroidetes, the latter mostly dominated by Bacteroides and Prevotella genera. Prevotella and Bacteroides are thought to have had a common ancestor. Formally, the two genera were differentiated in 1990. However classification is still undergoing, for example Bacteroides melaninogenicus has been reclassified and split into Prevotella melaninogenica and Prevotella intermedia. Either Prevotella or Bacteroides dominates the gut and they were proposed to be antagonistic. Prevotella is more common in non-Westernised populations consuming plant-rich diet. In Western populations it has also been associated with vegetarian or Mediterranean diets rich in fruits and vegetables. In accordance, genome analysis of Prevotella copri showed it was deficient in the ability to degrade host glycans and is more genetically equipped for plant glycan degradation. In a study of gut bacteria of children in Burkina Faso, Prevotella made up 53% of the gut bacteria, but were absent in age-matched European children. Studies also indicate that long-term diet is strongly associated with the gut microbiome composition—those who eat plenty of protein and animal fats typical of Western diet have predominantly Bacteroides bacteria, while for those who consume more carbohydrates, especially fibre, the Prevotella species dominate. However, Prevotella has been also associated to gut inflammation. It was demonstrated that increased levels of P. copri might contribute to chronic inflammation in HIV patients. One single species isolate P. copri CB7 has been used for different studies that showed it can be beneficial or detrimental, depending on the context. Prevotella is a large genus with high species diversity and high genetic diversity between strains. A recent study on Prevotella derived from humans compared the gene repertoires of its species derived from different body sites of human. It also reported an open pan- genome showing a vast diversity of the gene pool. In addition to genetic and overall microbiota differences in host the high genetic variety of Prevotella makes it difficult to predict their function that can be different in different individuals.
Prevotella species are also common vaginal commensals. Increased abundance of Prevotella in vaginal mucosa has been associated to bacterial vaginosis. Prevotella was shown to be the most heritable bacterial group in vaginal microbiome and its abundance was linked to body mass index and hormonal milieu. Prevotella bivia produces lipopolysaccharides and ammonia that are part of vaginal mucus. It is also associated with epithelial cytokine production and enhances the growth of other bacterial vaginosis-associated organisms, such as Gardnerella vaginalis. The later in turn was found to stimulate growth of P. bivia.
Pathogenicity
Prevotellaintermedia and Prevotella nigrescens were associated with inflammatory periodontal diseases, such as pregnancy gingivitis, acute necrotizing ulcerative gingivitis and adult periodontitis. Together with Porphyromonas gingivalis they are known as black-pigmenting anaerobes. All three require haemin as the source of iron for their growth. These species were shown to bind lactoferrin that is released together with the contents of neutrophils during inflammation and bleeding in periodontitis patients. Lactoferrin inhibits the growth of P. gingivalis but not the Prevotella species. Inorganic iron and iron-binding proteins such as transferrin and lactoferrin do not support the growth of P. intermedia, however hemin–iron-containing compounds which include hemin, human hemoglobin, bovine hemoglobin, and bovine catalase stimulate the growth of Prevotella intermedia. Hemoglobin-binding protein on the cell surface of P.intermedia has been described. P. copri has been correlated with onset of rheumatoid arthritis. An overgrowth of Prevotella and a reduction of Lactobacillus have been correlated with the onset of osteomyelitis in mice. The reduction of Prevotella in model mice led to an increase of Lactobacillus showing a protection effect against osteomyelitis. Thus, changes in the microbiota Prevotella may be related to the development of osteomyelitis.
