''Enterococcus'' is a large
genus
Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...
of
lactic acid bacteria of the
phylum
In biology, a phylum (; plural: phyla) is a level of classification or taxonomic rank below kingdom and above class. Traditionally, in botany the term division has been used instead of phylum, although the International Code of Nomenclature ...
Bacillota. Enterococci are
gram-positive
In bacteriology, gram-positive bacteria are bacteria that give a positive result in the Gram stain test, which is traditionally used to quickly classify bacteria into two broad categories according to their type of cell wall.
Gram-positive bact ...
cocci that often occur in pairs (
diplococci
A diplococcus (plural diplococci) is a round bacterium (a coccus) that typically occurs in the form of two joined cells.
Types
Examples of gram-negative diplococci are '' Neisseria spp.'' and ''Moraxella catarrhalis
''Moraxella catarrhal ...
) or short chains, and are difficult to distinguish from
streptococci
''Streptococcus'' is a genus of gram-positive ' (plural ) or spherical bacteria that belongs to the family Streptococcaceae, within the order Lactobacillales (lactic acid bacteria), in the phylum Bacillota. Cell division in streptococci occu ...
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 organism
A facultative anaerobic organism is an organism that makes ATP by aerobic respiration if oxygen is present, but is capable of switching to fermentation if oxygen is absent.
Some examples of facultatively anaerobic bacteria are ''Staphylococcus' ...
s, i.e., they are capable of
cellular respiration
Cellular respiration is the process by which biological fuels are oxidised in the presence of an inorganic electron acceptor such as oxygen to produce large amounts of energy, to drive the bulk production of ATP. Cellular respiration may be des ...
in both oxygen-rich and oxygen-poor environments.
Though they are not capable of forming
spore
In biology, a spore is a unit of sexual or asexual reproduction that may be adapted for dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores form part of the life cycles of many plants, algae, ...
s, enterococci are tolerant of a wide range of environmental conditions: extreme temperature (10–45 °C),
pH (4.6–9.9), and high
sodium chloride
Sodium chloride , commonly known as salt (although sea salt also contains other chemical salts), is an ionic compound with the chemical formula NaCl, representing a 1:1 ratio of sodium and chloride ions. With molar masses of 22.99 and 35. ...
concentrations.
Enterococci typically exhibit gamma-
hemolysis
Hemolysis or haemolysis (), also known by several other names, is the rupturing ( lysis) of red blood cells (erythrocytes) and the release of their contents ( cytoplasm) into surrounding fluid (e.g. blood plasma). Hemolysis may occur in viv ...
on sheep's blood agar.
History
Members of the genus ''Enterococcus'' (from
Greek
Greek may refer to:
Greece
Anything of, from, or related to Greece, a country in Southern Europe:
*Greeks, an ethnic group.
*Greek language, a branch of the Indo-European language family.
**Proto-Greek language, the assumed last common ancestor ...
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 infection
A urinary tract infection (UTI) is an infection that affects part of the urinary tract. When it affects the lower urinary tract it is known as a bladder infection (cystitis) and when it affects the upper urinary tract it is known as a kidne ...
s (see ''
Enterococcus faecalis''),
bacteremia
Bloodstream infections (BSIs), which include bacteremias when the infections are bacterial and fungemias when the infections are fungal, are infections present in the blood. Blood is normally a sterile environment, so the detection of microbe ...
,
bacterial endocarditis,
diverticulitis
Diverticulitis, specifically colonic diverticulitis, is a gastrointestinal disease characterized by inflammation of abnormal pouches— diverticula—which can develop in the wall of the large intestine. Symptoms typically include lower abdomi ...
,
meningitis
Meningitis is acute or chronic inflammation of the protective membranes covering the brain and spinal cord, collectively called the meninges. The most common symptoms are fever, headache, and neck stiffness. Other symptoms include confusion or ...
, and
spontaneous bacterial peritonitis
Spontaneous bacterial peritonitis (SBP) is the development of a bacterial infection in the peritoneum, despite the absence of an obvious source for the infection. It is specifically an infection of the ascitic fluid – an increased volume of pe ...
.
Sensitive strains of these bacteria can be treated with
ampicillin
Ampicillin is an antibiotic used to prevent and treat a number of bacterial infections, such as respiratory tract infections, urinary tract infections, meningitis, salmonellosis, and endocarditis. It may also be used to prevent group B str ...
,
penicillin
Penicillins (P, PCN or PEN) are a group of β-lactam antibiotics originally obtained from '' Penicillium'' moulds, principally '' P. chrysogenum'' and '' P. rubens''. Most penicillins in clinical use are synthesised by P. chrysogenum usin ...
and
vancomycin
Vancomycin is a glycopeptide antibiotic medication used to treat a number of bacterial infections. It is recommended intravenously as a treatment for complicated skin infections, bloodstream infections, endocarditis, bone and joint infection ...
.
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
A biofilm comprises any syntrophic consortium of microorganisms in which cells stick to each other and often also to a surface. These adherent cells become embedded within a slimy extracellular matrix that is composed of extracellular po ...
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
In science and engineering, an intrinsic property is a property of a specified subject that exists itself or within the subject. An extrinsic property is not essential or inherent to the subject that is being characterized. For example, mass ...
antibiotic resistance
Antimicrobial resistance (AMR) occurs when microbes evolve mechanisms that protect them from the effects of antimicrobials. All classes of microbes can evolve resistance. Fungi evolve antifungal resistance. Viruses evolve antiviral resistance. ...
. Some enterococci are intrinsically resistant to
β-lactam-based antibiotics (
penicillin
Penicillins (P, PCN or PEN) are a group of β-lactam antibiotics originally obtained from '' Penicillium'' moulds, principally '' P. chrysogenum'' and '' P. rubens''. Most penicillins in clinical use are synthesised by P. chrysogenum usin ...
s,
cephalosporin
The cephalosporins (sg. ) are a class of β-lactam antibiotics originally derived from the fungus ''Acremonium'', which was previously known as ''Cephalosporium''.
Together with cephamycins, they constitute a subgroup of β-lactam antibiotics ...
s,
carbapenem
Carbapenems are a class of very effective antibiotic agents most commonly used for the treatment of severe bacterial infections. This class of antibiotics is usually reserved for known or suspected multidrug-resistant (MDR) bacterial infections. S ...
s), 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
A hospital-acquired infection, also known as a nosocomial infection (from the Greek , meaning "hospital"), is an infection that is acquired in a hospital or other health care facility. To emphasize both hospital and nonhospital settings, it is so ...
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
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