Enterobacter

Definitions & Key takeaways

Enterobacter is a Gram-negative bacillus, facultative anaerobic, oxidase negative, and lactose fermenting bacteria that's known to cause nosocomial infections affecting the urinary tract, lungs, and other parts of the body. It's usually treated with antibiotics. It's diagnosed bia bacteria culture, of the blood, urine, or sputum, and treated with antibiotics.

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Enterobacter is a genus of Gram-negative rod-shaped bacteria which belongs to a family of bacteria called the Enterobacteriaceae.
There are several species which cause infection in humans and the most important are Enterobacter cloacae and Enterobacter aerogenes.
It’s an opportunistic pathogen, which can be normally found in the intestinal flora and causes a wide variety of hospital-acquired infections, mainly respiratory and urinary infections.
Now, a little bit of microbe anatomy and physiology. First, Enterobacter has a thin peptidoglycan layer, so it doesn’t retain the crystal violet dye during Gram staining.
Instead, like any other Gram-negative bacteria, it stains pink with safranin dye. And since it’s a Gram-negative bacillus, it looks like a little pink rod under the microscope.
Enterobacter is motile, non-spore forming, facultative anaerobic which means it can survive in both aerobic and anaerobic environments and oxidase negative which means it doesn’t produce an enzyme called oxidase.
Alright, now Enterobacter is urease positive which means it can produce an enzyme called urease that dissociates urea into carbon dioxide and ammonia.
This can be tested by transferring a pure sample of bacteria from the culture to a sterile tube containing a mixture of “urea agar” broth and phenol red.
Then, the mixture is incubated. So, with Enterobacter, urease makes urea dissociate into carbon dioxide and ammonia.
Ammonia then makes the mixture change color from orange-yellow to bright pink. Finally, Enterobacter grows well on MacConkey agar which is a medium that contains a pH sensitive dye and lactose.
This medium helps identify whether Gram-negative bacteria are lactose fermenters or not. Some Enterobacteriaceae, like Enterobacter, Klebsiella and Escherichia coli, can ferment lactose, which results in the production of acid, that makes the pH sensitive dye turn pink - so their colonies will be pink, while others, like Salmonella and Shigella, can’t ferment lactose so their colonies will be colorless.
Now, Enterobacter has very few notable virulence factors such as fimbriae, which help it attach to host cells, and they secrete hemolysins, which cause formation of tiny holes in the cell membrane, leading to cell damage.
So, an infection with Enterobacter can be acquired in two ways - endogenous and exogenous. So, because of its ubiquitary nature, meaning it can be found in water, soil, plants and in a lot of medical equipment and products, it can be transmitted in an exogenous way through direct or indirect contact.
Also, it can be transmitted in an endogenous way in people who are seriously ill and take a lot of antibiotics. Now, Enterobacter can be normally present in the intestinal flora, so, in people who take a lot of antibiotics, other species are destroyed, allowing proliferation of Enterobacter.
Now, Enterobacter is an opportunistic pathogen which causes nosocomial infections in people with prolonged hospitalization, in people with underlying illness such as malignancy, burns or diabetes, in case of immunosuppression, like in HIV positive individuals, and in the presence of a foreign device such as central venous catheters, endotracheal tubes or urinary catheters.
In people who are mechanically ventilated, Enterobacter causes respiratory infections like tracheobronchitis, which is inflammation of the trachea and bronchi, pneumonia, lung abscesses and pleural empyema which is a collection of pus within the pleural cavity.
In people with urinary catheters, Enterobacter causes urinary tract infections, or UTIs, like cystitis, pyelonephritis and prostatitis.
Now, the bacteria can be inoculated directly into the blood through a blood vessel catheter and it can cause a bloodstream infection, like bacteremia or sepsis.
The bacteria can also get into the bloodstream and cause endocarditis in people who use intravenous drugs. Now, in people with burns or with surgical wounds it can produce skin and soft tissue infections such as cellulitis, fasciitis, which is inflammation of the connective tissue surrounding muscles, blood vessels and nerves, myositis, which is inflammation of the muscles, and skin abscesses.
It can also cause intra-abdominal infections such as peritonitis following intestinal perforation or surgery. Symptoms depend on the disease.
So with respiratory infections in general, there may be chest pain, shortness of breath, and coughing. Tracheobronchitis may also associate wheezing, and with pneumonia, there may also be a fever and chills.
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. With prostatitis, there may be fever and chills, and the prostate may be swollen and tender on palpation.
With pyelonephritis, there may be flank pain, and systemic symptoms like fever, chills, nausea or vomiting. Next up, skin infections.
With cellulitis there may be swelling, erythema, tenderness and purulent drainage. Skin abscesses associate redness, heat, swelling and pain.
Fasciitis symptoms include fever, swelling and excessive pain, and with myositis there’s muscle weakness. Finally, with a bloodstream infection there may be fever, chills, hypotension and tachycardia, with peritonitis there may be abdominal pain and diffuse abdominal rigidity and endocarditis associates fever and new heart murmurs.
Enterobacter can be isolated in cultures from blood, sputum, urine or pus depending on the type of infection. For 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.
A chest X-ray may be done for respiratory infections, an abdominal CT scan or ultrasound can help diagnose abdominal infections, and echocardiography can help diagnose endocarditis.
Finally, Enterobacter infections can be treated with carbapenems, aminoglycosides, fluoroquinolones and polymyxins. Alright, as a quick recap, Enterobacter is a Gram-negative bacillus from the family Enterobacteriaceae.
It’s motile, non-spore forming, facultative anaerobic, oxidase negative, urease positive and lactose fermenter which means it forms pink colonies on MacConkey agar.
It’s an opportunistic pathogen which causes a wide variety of nosocomial infections such as lower respiratory tract infections, UTIs, bloodstream infection, skin and soft tissue infections, intra-abdominal infections and endocarditis.
Enterobacter infections are diagnosed by identifying the bacteria in a culture from blood, sputum, urine or pus, and can be treated with carbapenems, aminoglycosides, fluoroquinolones and polymyxins.