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Enterococcus – causes, symptoms, diagnosis, treatment, pathology


Learning medicine is hard work! Osmosis makes it easy. It takes your lectures and notes to create
a personalized study plan with exclusive videos, practice questions and flashcards, and so
much more. Try it free today! With Enterococcus, entero- refers to the intestines,
while -coccus means round shape. So Enterococcus is a genus of round bacteria
that commonly colonizes the gut of humans and animals. Enterococcus is also called Group D streptococcus
in Lancefield classification developed by an American microbiologist Rebecca Lancefield. There are two species that can cause infections
in humans and these are Enterococcus faecalis, amounting for the majority of infections,
and Enterococcus faecium, which causes disease more rarely. Now, looking at an individual bacterium, Enterococcus
has a thick peptidoglycan cell wall, which takes in purple dye when Gram stained – so
this is a gram-positive bacteria. When there’s more of them, Enterococci grow
in short chains, usually in pairs. They’re non-spore forming, facultative anaerobes,
meaning that they can survive in both aerobic and anaerobic environments and catalase negative,
which means they don’t produce an enzyme called catalase. Enterococci also can tolerate extreme environmental
conditions including high sodium chloride concentrations, high pH and even high temperatures. They can survive at 60 degrees Celsius for
up to 30 minutes! Ok, now, enterococcus is pyrrolidonyl arylamidase
positive, because it makes an enzyme called L-pyrrolidonyl arylamidase. To test for this, a small sample is taken
from a suspected bacterial colony, and then inoculated to a disk pad that’s embedded
with pyrrolidonyl beta naphthylamide – another joy of a word. With Enterococcus, pyrrolidonyl arylamidase
hydrolyzes pyrrolidonyl beta-naphthylamide to produce beta-naphthylamide. Try saying that 3 times fast! Finally, another reagent called N-methylamino-cinnamaldehyde
is added to the disk, and it reacts with beta-naphthylamide, resulting in a bright red color that confirms
Enterococcus is pyrrolidonyl arylamidase positive. Now, most commonly, Enterococci are gamma
hemolytic which means that when cultivated on blood agar they don’t induce hemolysis,
so the agar under and around the colony remains unchanged. But sometimes, they can induce alpha hemolysis,
also called partial hemolysis, which means that the agar under the colony turns dark
and greenish. Finally, it can grow on bile salts, which
is very useful to differentiate Enterococci from non-enterococcus group D streptococci. This can be demonstrated with the Bile-Esculin
test, that can be done on tubes or plates and uses a medium that contains peptone, beef
extract, bile, esculin, ferric citrate and agar. So, in the presence of bile, Enterococcus
can hydrolyze esculin into glucose and esculetin. Then, esculetin reacts with the ferric ions
supplied by ferric citrate and form a black diffusible complex. So, after 24 to 48 hours, Enterococci cause
a diffuse blackening of more than half of the tube or black halos around colonies on
plates. Now, Enterococci are opportunistic pathogens
which causes a wide variety of hospital-acquired infections, particularly in people with underlying
cardiovascular conditions, or in people with immunosuppressive conditions, like an HIV
infection. They also cause disease in people who have
been hospitalized for long periods of time and received multiple antibiotic treatments,
or in people with indwelling medical devices such as central venous catheters or urinary
catheters. Under these circumstances, Enterococcus mainly
causes infective endocarditis – in fact, Enterococcus is the second most common cause of infective
endocarditis overall. Enterococcus can get in the bloodstream one
of two ways. First, it can be inoculated directly into
the blood through a blood vessel catheter. Second, it may get in the bloodstream following
gastrointestinal or genitourinary surgery. From the bloodstream, Enterococcus reaches
the heart, where it sticks to the heart valves, forming bacterial vegetations. Most often, this is possible when there’s
underlying damage to the mitral or aortic valves. Next, in people with urinary catheters, Enterococcus
causes urinary tract infections, or UTIs, like cystitis and pyelonephritis. Finally, Enterococcus can cause other uncommon
infections such as biliary tract infections, because of its ability to grow in bile, surgical
wound infections such as cellulitis or skin abscesses, and intra-abdominal and pelvic
abscesses. Symptoms depend on the disease. With a bloodstream infection, there may be
fever, chills, hypotension and tachycardia and with endocarditis, there may be fever,
new heart murmurs and malaise. With urinary tract infections in general,
symptoms include dysuria, which is pain or a burning sensation during urination, urinary
frequency, which means needing to urinate more often than usual and urinary urgency,
which means strong need to urinate. With cystitis, there’s also suprapubic pain
and with pyelonephritis, there may be flank pain, and systemic symptoms like fever, chills,
nausea or vomiting. With skin infections, there may be swelling,
erythema, or redness, tenderness or pain, and purulent drainage. Finally, with biliary tract infections, there
may be fever, pain and jaundice and with intra-abdominal and pelvic abscesses there may be fever, abdominal
pain, nausea and vomiting. Diagnosis is based on isolating enterococcus
in blood, urine or pus cultures, depending on the type of infection. With infective endocarditis, an echocardiogram
may show bacterial vegetations on the heart valves. With UTIs, the urinalysis shows an alkaline
urine pH, above 7, pyuria which means white blood cells in the urine, and bacteriuria,
which means bacteria in the urine. An abdominal or pelvic ultrasound or CT scan
can diagnose biliary tract infections as well as abdominal or pelvic abscesses. Treatment for infections caused by Enterococcus
faecalis is usually done with beta-lactams such as penicillin or ampicillin, or aminoglycosides
such as gentamicin or streptomycin. Resistant strains can be treated with vancomycin. Most strains of Enterococcus faecium, on the
other hand, are highly resistant to beta-lactams and aminoglycosides. So, in this case, vancomycin is used from
the get-go. Sadly, both Enterococcus faecalis and Enterococcus
faecium can become resistant even to vancomycin. These are called vancomycin-resistant Enterococcus,
or VRE for short, and require treatment with expensive antibiotics like linezolid, daptomycin
or tigecycline. Alright, as a quick recap, Enterococcus is
a Gram-positive round bacteria, non-spore forming, facultative anaerobic and catalase
negative. It can survive in extreme conditions such
as high sodium chloride concentration, high pH and extreme temperature. It can have alpha or gamma hemolysis on blood
agar and it can grow on bile salts. It’s an opportunistic pathogen which causes
a wide variety of hospital-acquired infections like UTIs, endocarditis, bloodstream infections,
biliary tract infections, wound infections and intra-abdominal infections. For diagnosis, it can be isolated in cultures
from blood, urine or pus depending on the type of infection. For treatment, E. faecalis can be treated
with beta-lactams, aminoglycosides and vancomycin, and E. faecium can be treated with vancomycin. In case of VRE, it can be treated with linezolid,
daptomycin or tigecycline.

7 thoughts on “Enterococcus – causes, symptoms, diagnosis, treatment, pathology

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