Enterococcus

Enterococcus
Enterococcus sp. infection in pulmonary tissue
Scientific classification
Domain:	Bacteria
Phylum:	Firmicutes
Class:	Bacilli
Order:	Lactobacillales
Family:	Enterococcaceae
Genus:	Enterococcus (ex Thiercelin & Jouhaud 1903) Schleifer & Kilpper-Bälz 1984
Species[3]
E. alcedinis[1] [1] [1] E. avium[1] [1][2] [1] [1] [1] [1] [1] [1] [1] [1] [1] [1] [1] [1] E. durans[1] [1] E. faecalis[1] E. faecium[1] E. gallinarum[1] [1] E. haemoperoxidus[1] [1] E. hirae[1] [1] [1] [1] [1] E. malodoratus[1] [1] [1] E. moraviensis[1] E. mundtii[1] [1] [1] [1] [1] E. pseudoavium[1] [1] E. raffinosus[1] [1] [1] [1] [1] [1] [1] [1] E. solitarius [1] [1] [1] [1] [1] [1] [1] [1] [1] E. xinjiangensis[1]

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.^[4] 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.^[4]

Physiology and classification[]

Enterococci are facultative anaerobic organisms, i.e., they are capable of cellular respiration in both oxygen-rich and oxygen-poor environments.^[5] Though they are not capable of forming spores, enterococci are tolerant of a wide range of environmental conditions: extreme temperature (5–65 °C), pH (4.5–10.0), and high sodium chloride concentrations.^[6]

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.^[7]

Evolution[]

This genus appears to have evolved 425 million years ago to 500 million years ago.^[8]

Pathology[]

Important clinical infections caused by Enterococcus include urinary tract infections (see Enterococcus faecalis), bacteremia, bacterial endocarditis, diverticulitis, meningitis, and spontaneous bacterial peritonitis.^[6][9][10] Sensitive strains of these bacteria can be treated with ampicillin, penicillin and vancomycin.^[11] Urinary tract infections can be treated specifically with nitrofurantoin, even in cases of vancomycin resistance.^[12]

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.^[13] New epidemiological evidence has shown that enterococci are major infectious agent in chronic bacterial prostatitis.^{[citation needed]} 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.^[9] 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.^[6] Other developed countries, such as the UK, have been spared this epidemic, and, in 2005, Singapore managed to halt an epidemic of VRE.^[14] Although quinupristin/dalfopristin (Synercid) was previously indicated for treatment of VRE in the USA, the FDA approval for this indication has since been retracted.^[15] The rationale for the retraction of Synercid's indication for VRE was based upon poor efficacy in E. faecalis, which is implicated in the vast majority of VRE cases.^[16][17] Tigecycline has also been shown to have antienterococcal activity, as has rifampicin.^{[citation needed]}

Water quality[]

In bodies of water, the acceptable level of contamination is very low; for example in the state of Hawaii, and most of the United States, the limit for water off its beaches is a five-week geometric mean of 35 colony-forming units per 100 ml of water, above which the state may post warnings to stay out of the ocean.^[18] In 2004, Enterococci sp. took the place of fecal coliforms as the new USA federal standard for water quality at public saltwater beaches and Escherichia coli at freshwater beaches.^[19] It is believed to provide a higher correlation than fecal coliform with many of the human pathogens often found in city sewage.^[20]

References[]

External links[]