Enterococcus Species
Enterococcus species causes Urinary tract infections, biliary tract infections, ulcers like bed sores, wounds especially in abdomen.
Endocarditis and meningitis is also caused by this organisms.
It is rare but may be life threatening disease.
Enterococcus faecalis (E. faecalis) and Enterococcus faecium (E. faecium) are the clinically important organisms.
Enterococcus faecalis is the main pathogen in Enterococcus genus which is responsible for about 95% of the Enterococcal infections.
Enterococci are part of the normal flora of the female genital tract, intestinal tract, and urethra.
This organism may enter the bloodstream during the procedures done in gastrointestinal tract and genitourinary tract.
Moreover, this organisms can colonize the skin and oral mucous membrane, especially in hospitalized patients.
Enterococcus faecium may cause minority of infections. Enterococci do not produce exotoxins or virulence factors.
Enterococcus species are Gram positive cocci in Gram stained smears.
Normally occurring in pairs or short chains.
Majority of organisms are non-motile and non-capsulated.
They are aerobic organisms which can grow in wide range of temperatures, 10ºC – 45ºC.
Colony morphology
Blood agar
Colonies are small 0.5mm – 1 mm, round and opaque.
Shows Alfa, Beta or non haemolytic colonies on blood agar.
They are mainly non haemolytic.
MacConkey agar
Ferment lactose and produce small dark red magenta colour colonies.
CLED agar
Produce small yellow colonies on CLED (cysteine lactose electrolyte-deficient) agar.
Chromogenic agar
On chromogenic agar, it produce small turquoise blue colonies.
Catalase negative organism.
Enterococci hydrolyze bile esculin.
They have ability to survive in the presence of bile.
Hydrolyze the polysaccharide esculin and turn the esculin medium into black, giving a positive bile esculin test.
This test is useful to distinguish enterococci from non enterococcal group D streptococci.
Moreover, Enterococci grow in 6.5% sodium chloride.
It is useful for the confirmation of this organism.
These organisms are positive for PYR (pyrazin amidase) test.
E. faecium can be distinguished from E. faecalis by studying the fermentation patterns.
Normally they are evaluated in clinical laboratories.
Furthermore, Enterococcus species ferment lactose, mannitol and other sugars.
Treatment
Being resistant to cephalosporins and sensitive to ampicillin is common feature of most enterococci.
Resistance has identified against penicillin.
Vancomycin and ampicillin resistance is emerging in hospital acquired infections.
Though these drugs are ineffective individually, they are effective when treated with combination of several drug classes.
It is known as the synergistic action.
As an example, it is useful when treated with penicillin or vancomycin plus aminoglycosides such as gentamicin.
They have a synergistic effect.
Aminoglycosides alone ineffective for the treatment as it cannot penetrate the cell wall.
Vancomycin or Penicillin destroy the cell wall of the organisms and then aminoglycoside can penetrate the cell wall and attack the organism.
Linezolid can be used to treat the Vancomycin resistant strains.
Prevention
For the patients with damaged heart valves should be treated with penicillin and gentamicin prior to the procedures relate to the urinary tract or intestinal tract.
Rules and regulations should be implemented to control the usage of antibiotics unnecessarily to prevent the multiple drug resistance.
There is no a vaccine available against Enterococal infections.
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