Enterococcus faecalis is the most commonly isolated of the genera. According to Elmer Koneman, M.D., it is associated with 80 to 90 percent of human enterococcal infections. Enterococcus faecalis, as the name implies, is found normally in the intestines of humans, animals and birds. It is also found in soil and water in nature. Enterococcus faecalis has been implicated in a wide variety of human infections and is a notorious problem in hospital-acquired infections.
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Microscopic and Colony Morphology
Enterococcus faecalis and all of the enterococci are closely related to the streptococci and appear microscopically as spheres or cocci. They also divide by binary fission to form chains of bacteria. Use of the Gram stain technique shows that the bacterial cells are purple or Gram-positive.
When Enterococcus faecalis is grown of bacteriological agar that contains blood, it typically appears as small gray colonies that lack a zone of hemolyzed cells surrounding the colony.
What makes Enterococcus faecalis pathogenic is less clear than with many other microorganisms. What is known is that some strains produce hemolysins that can cause some toxicity. It is also a substance that allows the bacteria to clump together and adhere to cells of the body. The fact that Enetrococcus faecalis can be resistant to a wide array of antibiotics must contribute to the proliferation of the organism.
Causes Disease and Infections
Because Enterococcus faecalis is normally found in the intestinal tract of people, it easily becomes a contamination problem in hospital and institutional settings. Because of the debilitated status of hospitalized patients and the antibiotic resistance of the organism, it can cause many types of infections. The infection most commonly caused by E. faecalis is urinary tract infections (UTI). Most enterococcal UTI's are nosocomial (hospital-acquired) in nature or related to abnormalities of the urinary tract. Bacteremia with E. faecalis is usually the result of infections from other sites, like the urinary tract. Wound infections, particularly in the abdominal area, are frequently seen. It is also commonly seen in cases of endocarditis.
Resists a Variety of Antibiotics
One of the most important and serious factors about Enterococcus faecalis and the other enterococci is its resistance to a variety of antibiotics. This also contributes to its ability to cause disease. Most antibiotics used for systemic infections singly that are effective against other types of Gram-positive cocci (staphylococci and streptococci) are ineffective against E. faecalis. Treatment typically involves the synergistic treatment of an antibiotic that attacks the cell wall like penicillin or vancomycin and a aminoglycoside like gentamicin. Resistance to vancomycin is becoming increasingly common. Treating E. faecalis UTI's are usually easier to treat with antibiotics.