What is enterococcus?

Definition

Enterococcus is a bacterium that is normally found in the human intestinal tract. The bacterium can cause a number of infections in humans.

Natural Habitat and Features

Enterococci are part of the normal bacterial flora of the human intestine. They are also found naturally in the intestines of nonhuman animals and of birds. Although most commonly found in the bowel, enterococci can also be present in the vagina, skin, and upper respiratory tract. In the environment, enterococci can be found in surface water, plants, and soil.

Although there are seventeen species of enterococci, the most common species found in humans are faecalis and faecium. Other species known to cause infection in humans include avium, casseliflavus, durans, gallinarum, mundtii, and raffinosus. Enterococci are gram-positive anaerobic cocci that grow in short chains. Under a microscope, enterococci appear spherical. They are extremely hardy and can grow and survive under a variety of conditions. They can survive in temperatures ranging from 50° to 113° Fahrenheit (10° to 45° Celsius), under aerobic or anaerobic conditions, under hypotonic or hypertonic conditions, and in acidic or alkaline environments. Unlike most microorganisms, they can grow in 6.5 percent sodium chloride and in concentrated bile salts.

Pathogenicity and Clinical Significance

There are a number of infections that are caused by enterococci. Common
infections include those of wounds, the urinary tract, the heart valve
(endocarditis), the bloodstream (bacteremia),
and the intra-abdomen and pelvis, and infection and inflammation of the protective
membranes of the brain (meningitis).

Many enterococcal infections are spread by colonized persons (people whose
normal intestinal flora has spread to the urinary tract, the abdomen, or other
parts of the body without causing disease). There are certain factors that may put
a person at risk for enterococcus colonization. Colonization risk factors include
the following: prolonged hospitalization, admission to an intensive care unit,
receiving a transplant, having a compromised immune system, undergoing a lengthy
course of antibiotics, having renal insufficiency, and providing
patient care in a health care setting.

The majority of enterococcal infections are nosocomial (hospital acquired) infections, many of which are spread from colonized patients to other patients by health care workers. Enterococci can live on surfaces for several weeks, so infection can easily be spread through contact with contaminated items (fomites) such as bed rails, door knobs, faucets, and sinks. Inadequate handwashing technique also contributes to the spread of Enterococcus.

The most common type of nosocomial infection is urinary tract infection (UTI), although Enterococcus is not the only bacterium known to cause nosocomial UTI. Most nosocomial UTIs are the result of inadequate handwashing, the inappropriate use of urinary catheters, and the mismanagement of indwelling urinary catheters.

Another common nosocomial enterococcal infection is bacteremia, which is frequently associated with the use of central venous catheters. Serious catheter-related bloodstream infections can develop quickly because central venous catheters are placed in major veins. Nosocomial bacteremia is usually a result of inadequate handwashing, lack of appropriate barrier precautions during insertion, poor choice of placement site, improper cleaning of the insertion site, and a lack of patient education about site care at home.

Drug Susceptibility

Enterococcal infections can be difficult to treat because
Enterococcus has not only an intrinsic resistance to
antibiotics but also an acquired resistance. Before beginning treatment for an
enterococcal infection, isolated organisms should be tested for resistance to
beta-lactam antibiotics (such as penicillin and cephalosporin), glycopeptides
(vancolycin and tycoplanin), aminoglycosides (gentamycin and
streptomycin), macrolides (erythromycin and tetracycline), and quinolones
(ofloxacin and ciprofloxacin).

Most enterococcal infections are treated using a combination of antibiotics:
one (such as ampicillin or vancomycin) that attacks the cell wall and an
aminoglycoside, which inhibits protein synthesis. In the past several years,
enterococci have become resistant to vancomycin, making it increasingly difficult
to treat enterococcal infections. There are some newer antibiotics that have been
found to be effective against vancomycin-resistant enterococci (VRE).
These antibiotics include quinupristin/dalfopristin, linezolid, daptomycin, and
tigecycline. However, incidences of resistance to these newer antibiotics also
have been reported. As with other types of enterococcal infection, treatment of
VRE requires laboratory testing for resistance to determine what antibiotics will
be effective as treatment.

Bibliography

Barie, Philip S., and Steven M. Opal. “Infectious Complications Following Surgery and Trauma: Bloodstream Infection.” In Cohen and Powderly Infectious Diseases, edited by Jonathan Cohen, Steven M. Opal, and William G. Powderly. 3d ed. Philadelphia: Mosby/Elsevier, 2010. Addresses the risk of opportunistic infection, especially bloodstream infection, following surgery or injury.

Durack, David T., and Michael H. Crawford, eds. Infective Endocarditis. Philadelphia: W. B. Saunders, 2003. A text on all aspects of endocarditis, which is caused by bacteria, including Enterococcus.

EBSCO Publishing. DynaMed: Vancomycin-Resistant Enterococci (VRE) Infection. Available through http://www.ebscohost.com/dynamed.

Fraser, Susan, and Julie Lim. “Enterococcal Infection.” Available at http://emedicine.medscape.com/article/216993-overview. A good discussion of enterococcal infections, including frequency, pathophysiology, history, diagnosis, treatment, prevention, and drug susceptibility.

Johns Hopkins Hospital and Johns Hopkins Health System. “Vancomycin Resistant Enterococci (VRE).”Available at http://www.hopkinsmedicine.org/heic/ID/vre. An overview of vancomycin-resistant enterococci that includes information about the organism, epidemiology, disease description, diagnosis, treatment, and infection prevention and control.

The Nurse’s Role in Infection Prevention and Control. Oakbrook Terrace, Ill.: Joint Commission Resources, 2010. A book for health care workers and health care organization administrators that discusses methods for preventing and controlling the spread of infection in the health care setting.