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''Enterococcus'' is a large genus of lactic acid bacteria of the phylum Bacillota. 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: ''E. faecalis'' (90–95%) and '' E. faecium'' (5–10%). Rare clusters of infections occur with other species, including ''E. casseliflavus'', '' E. gallinarum'', and ''E. raffinosus''.

Physiology and classification

Enterococci are facultative anaerobic organisms, i.e., they are capable of cellular respiration in both oxygen-rich and oxygen-poor environments. Though they are not capable of forming spores, enterococci are tolerant of a wide range of environmental conditions: extreme temperature (10–45 °C), pH (4.6–9.9), and high sodium chloride concentrations.

Enterococci typically exhibit gamma- hemolysis on sheep's blood agar.

History

Members of the genus ''Enterococcus'' (from Greek έντερο, ''éntero'', "intestine" and κοκκος, ''coccos'', "granule") were classified as group D '' Streptococcus'' until 1984, when genomic DNA analysis indicated a separate genus classification would be appropriate.

Evolution

This genus appears to have evolved to .Lebreton F, Manson AL, Saavedra JT, Straub TJ, Earl AM, Gilmore MS (2017) Tracing the Enterococci from Paleozoic origins to the hospital. Cell 169(5):849-861.e13. doi: 10.1016/j.cell.2017.04.027

Pathology

Important clinical infections caused by ''Enterococcus'' include urinary tract infections (see '' Enterococcus faecalis''), bacteremia, bacterial endocarditis, diverticulitis, meningitis, and spontaneous bacterial peritonitis. Sensitive strains of these bacteria can be treated with ampicillin, penicillin and vancomycin. Urinary tract infections can be treated specifically with nitrofurantoin, even in cases of vancomycin resistance.

Meningitis

Enterococcal meningitis is a rare complication of neurosurgery. It often requires treatment with intravenous or intrathecal vancomycin, yet it is debatable as to whether its use has any impact on outcome: the removal of any neurological devices is a crucial part of the management of these infections.
New epidemiological evidence has shown that enterococci are major infectious agent in chronic bacterial prostatitis. Enterococci are able to form biofilm in the prostate gland, making their eradication difficult.

Antibacterial resistance

From a medical standpoint, an important feature of this genus is the high level of intrinsic antibiotic resistance. Some enterococci are intrinsically resistant to β-lactam-based antibiotics (penicillins, cephalosporins, carbapenems), as well as many aminoglycosides. In the last two decades, particularly virulent strains of ''Enterococcus'' that are resistant to vancomycin ( vancomycin-resistant ''Enterococcus'', or VRE) have emerged in nosocomial infections of hospitalized patients, especially in the US. Other developed countries, such as the UK, have been spared this epidemic, and, in 2005, Singapore managed to halt an epidemic of VRE. Although quinupristin/dalfopristin">.2.2ct-3-ylthio">.2.2.html" ;"title="3''S'')-1-azabicyclo[2.2.2">3''S'')-1-azabicyclo[2.2.2ct-3-ylthioethyl}-22-[4- ...