TAXONOMY: Bacteria -> Terrabacteria group -> Firmicutes -> Bacilli -> Lactobacillales -> Enterococcaceae -> Enterococcus
'Enterococcus' is a large genus of lactic acid bacteria of the phylum Firmicutes. Enterococci are Gram-positive cocci that often occur in pairs (diplococci) or short chains, and are difficult to distinguish from streptococci on physical characteristics alone. Two species are common commensal organisms in the intestines of humans: Enterococcus faecalis E. faecalis (90-95%) and Enterococcus faecium E. faecium (5-10%). Rare clusters of infections occur with other species, including E. casseliflavus, Enterococcus gallinarum E. gallinarum, and E. raffinosus. The genus Enterococcus presently contains 43 recognised species occurring in a wide variety of environments. Enterococci are naturally associated with the gastrointestinal tract of humans and animals, however they may be isolated from food, especially from meat, dairy and plant food fermentations, as well as from the environment.
The Enterococci inhabit harsh environments, like the intestinal tracts of humans and animals. Growth under these hostile conditions requires that E. faecalis have a metabolism that is flexible. E. faecalis are capable of not only fermentation to produce lactic acid but also can “catabolize a spectrum of energy sources from carbohydrates, glycerol, lactate, malate, citrate, diamino acids and many α-keto acids”. It has been shown that under selected growth conditions E. faecalis can enhance growth through oxidative phosphorylation using a proton motive force established by electron transport. A consequence of “nascent respiration is production of potent oxidants” (e.g. superoxide and hydrogen peroxide), oxidative stress the E. faecalis can tolerate. The tolerance of this stress, combined with other severe growth conditions, allows the E. faecalis to grow at 10 to 45°C, in bile salts, and at extremely low and high pHs. In addition, E. faecalis can resist azide, detergents, heavy metals, and ethanol. Since E. faecalis can utilize varied sugar sources it can live in diverse environments, especially in the intestine where nutrients are limited. In the intestine, E. faecalis derive most of their energy from the fermentation of non-absorbed sugars. E. faecalis can also get energy by degrading mucins, a carbohydrate that is heavily glycosylated and produced by intestinal goblet cells.
They are frequent causes of hospital-acquired infections in immunocompromised patients, in patients receiving surgery or in patients with severe underlying diseases. Production of a variety of virulence factors and high intrinsic and acquired resistances to multiple antibiotics among some enterococcal strains often complicates proper treatment. On the other hand, some enterococcal strains have beneficial properties which are utilized in the development of starter cultures for food fermentations or as probiotics. Gram-positive. Cells are ovoid, occur singly, in pairs, or in short chains, and are frequently elongated in the direction of the chain. Nonsporeforming. Strains of some species may be motile by scanty flagella. Some species are yellow pigmented. Facultatively anaerobic. Certain species are carboxyphilic (CO2-dependent). Catalase-negative, but some strains reveal pseudocatalase activity when cultivated on blood-containing agar media. Hemolytic activity is variable and largely species-dependent.
DNA G+C content (mol%): 35.1–44.9.
Type species: Enterococcus faecalis
This genus contains microbial species that can reside in the human gastrointestinal tract. [PMC 4262072]
A significant association was observed between commensal microbial composition and clinical response to anti-PD-1-based immunotherapy. Bacterial species more abundant in responders included Bifidobacterium longum, Collinsella aerofaciens, and Enterococcus faecium. PMID: 29302014