Enterococcus faecalis and faecium
last authored: Feb 2010, David LaPierre
last reviewed:
Introduction
Enteroccocus are bacteria similar to Streptococcus. They are found in large numbers in the colon, (ie 107 / gram of stool) and in the genitourinary tract. Notmally they do not cause disease, but they can also lead to urinary tract infections, wound infections, endocarditis, intra-abdominal abscesses, and bacteremia.
Especially important is the capacity of Enteroccocus to develop antibiotic resistance, most fearfully to vancomycin.
The Case of Bill Bradley
Bill is a 68 year-old man admitted to hospital with a per-rectal abscess and fever, diagnosed as caused by MRSA. He is treated with vancomycin. Three days later, his fever returns, and the urine in his catheter bag is dark and cloudy. Enterococcus is identified in urine culture.
Why is his situation a serious one?
Epidemiology
Enterococcus is virtually ubiquitous in gut flora. Antibiotic-resistant Enterococcus strains are growing in various centres around the world.
Classification and Characteristics
Enteroccoci are gram positive cocci arranged in pairs or short chains.
They are facultatively anaerobic and grow in presence of 6.5% NaCl and 40% bile.
They have no serious virulence factors, though antibiotic resitance is of substantial concern. Adhesion factors mediate binding to host.
Transmission and Infection
Most human infections are from patient's own flora, though the bacteria can also be transferred person-to-person or through consumption of contaminated food or water.
Nosocomial infections are a serious source of spread. Infection control measures are of critical importance.
Clinical Manifesations
As many strains are completely resistant to antibiotics, enterococci are a leading cause of nosocomial infections.
Urinary tract infections and sepsis are most common.
Endocarditis is a severe complication
Enterococcus can also be found in intra-abdominal absecesses and wounds, though their significance is not clear.
Diagnosis
Enterococcus are distinguished from Streptococcus by their resistance to dissolving in bile and high salts.
Treatment
Enterococcus has innate resistance to many classes of antibiotics:
- penicillins are bacteriostatic, rather than bacteriocidal as they are in other bacteria
- intrinsic resistance to aminoglycosides
- E. faecium is 90% resistant to ampicillin, while E. faecalis is almost always sensitive
A combination of a beta-lactam and an aminoglycoside can be effective (synergy).
Highest-level drugs include dalfopristin-quinupristin (for E. faecium), linezolid, and daptomycin. Resistance to some of these antibiotics is already being reported.
Resources and References
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