Klebsiella pneumoniae
Definitions & Key takeaways
Klebsiella pneumoniae is a gram-negative, non-spore-forming, rod-shaped bacterium that is known to cause diseases in humans such as pneumonia, meningitis, septicemia, and urinary tract infections. Klebsiella pneumoniae is a facultative anaerobe, and lactose-fermenter, and is also able to produce an enzyme known as beta-lactamase, which makes it resistant to several antibiotics.
Klebsiella pneumoniae is a Gram-negative rod-shaped bacteria, which belongs to a family of bacteria called the Enterobacteriaceae.
Klebsiella pneumoniae can normally colonize the oropharynx and the gastrointestinal tract. It causes various hospital-acquired infections, such as pneumonia (hence the name) and is the third most common cause of urinary tract infections.
CharacteristicsNow, Klebsiella pneumoniae has a thin peptidoglycan layer, so like other Gram-negative bacteria, it stains pink.
And since it’s a bacillus, it looks like a little pink rod under the microscope.Klebsiella pneumoniae is non-motile, non-spore forming, and facultative anaerobe.
This means it can live even without oxygen, although it grows better in an aerobic environment. So, it prefers places like lungs,throat, or respiratory airways, as well as ventilators in the ICU where there is an unlimited flow of oxygen.
Alright, now Klebsiella pneumoniae 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 Klebsiella, urease makes urea dissociate into carbon dioxide and ammonia.
Ammonia then makes the mixture change color from orange-yellow to bright pink.Finally, Klebsiella pneumoniae 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 Klebsiella, Enterobacter, and Escherichia coli, can ferment lactose.
This results in the production of the acid that makes the pH sensitive dye turn pink - so their colonies will be pink. Klebsiella has an abundant polysaccharide capsule which leads to the formation of very mucoid and viscous pink colonies.
Others like Salmonella and Shigella can’t ferment lactose, so their colonies will be colorless. Pathogenesis and virulence factorsNow, Klebsiella pneumoniae has a number of virulence factors that are like assault weaponry that help it attack and destroy the host cells and evade the immune system.First, Klebsiella pneumoniae is encapsulated, which means it’s covered by a polysaccharide layer called a capsule.
This capsule is a major virulence factor because of its antiphagocytic ability. This means that it protects the bacteria against phagocytosis by macrophages and neutrophils, allowing Klebsiella to escape destruction.
On the capsule, there are pili, which are hair-like extensions that help the bacteria attach to host cells. Underneath the capsule, there’s an outer membrane, which consist of lipopolysaccharides, or LPS.
Now, LPS has the ability to avoid complement-mediated killing by inhibiting the formation of the membrane attack complex and preventing membrane damage and bacterial cell death.
Finally, it needs iron to thrive and replicate, so it produces a siderophore, which is a term used for a group of small, high-affinity, iron chelating compounds that snatch iron from host cells.
In the urinary tract, Klebsiella can also use urease to convert the urea that’s normally present in urine to ammonia and carbon dioxide.
This can combine with ammonium to form struvite stones that often form large staghorn renal calculi, or kidney stones. Finally, this leads to urinary stasis, which starts a vicious circle, promoting bacterial multiplication, urinary alkalinization, and the deposition of new layers of struvite.
Diseases and risk factorsNow, Klebsiella pneumoniae can cause various hospital-acquired infections in people with underlying illnesses (like diabetes) and in the presence of foreign devices like central venous catheters, endotracheal tubes, or urinary catheters.
Classically, in people with diabetes or in those with alcohol dependence, it causes lobar pneumonia. This is associated with formation of lung abscesses due to aspiration of microbes from the oropharynx to the lower respiratory tract.
In people with urinary catheters, it causes urinary tract infections, or UTIs, like cystitis, pyelonephritis, or prostatitis.
In people with blood vessel catheters, the bacteria can be inoculated directly into the bloodstream, which leads to a bloodstream infection called bacteremia, and from there it can spread to the heart, causing endocarditis, or to the brain, causing meningitis.
Finally, in people with cirrhosis and ascites, it can infect the peritoneal fluid and cause spontaneous bacterial peritonitis.
SymptomsSymptoms depend on the disease. With lobar pneumonia, there is high fever, chills, chest pain, shortness of breath, and a productive cough with blood-tinged sputum called red currant jelly sputum.
With urinary tract infections, symptoms include dysuria, which is pain or a burning sensation during urination; urinary frequency, meaning needing to urinate a lot; and urinary urgency, which means a strong need to urinate.
With cystitis, there’s also suprapubic pain. With prostatitis, there may be fever and chills, and a swollen, tender prostate on palpation.
With pyelonephritis, there may be flank pain, fever, and nausea or vomiting. Next, with a bloodstream infection, there may be fever and hypotension and tachycardia.
Finally, with spontaneous bacterial peritonitis, there may be fever, chills, and extreme abdominal pain.DiagnosisFor diagnosis, Klebsiella pneumoniae can be isolated in cultures from blood, sputum, or urine 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.
Also, a complete blood count can be done which shows leukocytosis. Finally, a chest X-ray can be done in case of pneumonia, which may show cavitary lesions in the upper lobes if there’s an abscess formation.
TreatmentKlebsiella pneumoniae is a multidrug resistant bacterium, which produces different enzymes that break down the structure of antibiotics.
So, it produces beta-lactamases, which confers resistance against ampicillin and amoxicillin. In this case, it can be treated with cephalosporins, aminoglycosides, fluoroquinolones, and carbapenems.
Now, there are strains that produce extended-spectrum beta-lactamases (or ESBL), which confers resistance to cephalosporins, aminoglycosides, and fluoroquinolones, so those strains are usually treated with carbapenems.
However, there are strains who produce carbapenemases that confers resistance even to carbapenems. So, in this case, Klebsiella can be treated with colistin, tigecycline, or fosfomycin.##SummaryAlright, as a quick recap.
Klebsiella pneumoniae is a Gram-negative bacillus, non-motile, non-spore forming, facultative anaerobe, urease positive, and lactose fermenter, which forms mucoid pink colonies on MacConkey agar.
It has a bunch of virulence factors such as capsule, LPS, pili, and a siderophore, which helps the bacteria to attack and destroy the host cells and evade the immune system.
It causes various hospital-acquired infections such as pneumonia, UTIs, bacteremia, endocarditis, and meningitis. For diagnosis, it can be isolated in cultures from blood, sputum, or urine.
It’s a multidrug resistant bacteria, and it can be treated with cephalosporins, aminoglycosides, fluoroquinolones, and carbapenems in case of beta-lactamase production; only with carbapenems in case of ESBL production; and with colistin, tigecycline or fosfomycin in case of carbapenemases production.
and it can be treated with cephalosporins aminoglycoside fluoroquinolones and carbapenem In case of beta lactamase production only with carbapenem in case of ESB L production and with colistin tigecycline or psyc in case of carbapenem
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