Enterococcus
Enterococcus is a type of bacterium commonly found in the human intestinal tract and is also present in the intestines of nonhuman animals and birds. While Enterococcus is a normal part of the intestinal flora, it can cause various infections in humans, including urinary tract infections, endocarditis, bacteremia, and meningitis. The most prevalent species in humans are Enterococcus faecalis and Enterococcus faecium, although other species can also lead to infections. Enterococci are gram-positive anaerobic cocci that are notably resilient, surviving in a wide range of environmental conditions, including extreme temperatures and salinity.
Infections caused by Enterococcus are often hospital-acquired, particularly affecting individuals with compromised immune systems or those undergoing invasive medical procedures. Their ability to live on surfaces for extended periods contributes to the spread of infections in healthcare settings. Treating enterococcal infections can be challenging due to their intrinsic and acquired antibiotic resistance. Effective management often requires laboratory testing to determine the most appropriate antibiotics, including newer treatments for vancomycin-resistant enterococci (VRE). Ongoing research and development are exploring preventive strategies and alternative therapies to combat these resilient bacteria.
Enterococcus
Transmission route: Blood, direct contact
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 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 healthcare 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 a treatment. Newer preventative therapies have also been developed. These include probiotic cocktails, revolutionary antimicrobial surface coatings for medical equipment like catheters, antibody therapy, and phage therapy.
Bibliography
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Durack, David T., and Michael H. Crawford, eds. Infective Endocarditis. Philadelphia: W. B. Saunders, 2003.
EBSCO Publishing. DynaMed: Vancomycin-Resistant Enterococci (VRE) Infection. Available through www.ebscohost.com/dynamed.
“Enterococcus Infections - StatPearls.” NCBI, 2 May 2022, www.ncbi.nlm.nih.gov/books/NBK567759/. Accessed 28 Feb. 2023.
Fraser, Susan, and Julie Lim. “Enterococcal Infection.” Available at http://emedicine.medscape.com/article/216993-overview.
Johns Hopkins Hospital and Johns Hopkins Health System. “Vancomycin Resistant Enterococci (VRE).”Available at www.hopkinsmedicine.org/heic/ID/vre.
The Nurse’s Role in Infection Prevention and Control. Oakbrook Terrace, Ill.: Joint Commission Resources, 2010.