Klebsiella pneumoniae

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Klebsiella pneumoniae


Introduction to bacteria

Bacterial structure and functions


Klebsiella pneumoniae


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USMLE® Step 1 questions

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Klebsiella pneumoniae

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USMLE® Step 1 style questions USMLE

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A 42-year-oldman presents to the emergency department with a fever and a cough productive of blood-tinged sputum. He is currently undomiciled. Temperature is 39 °C (102.2 °F), pulse is 114/min, respirations are 23/min, and blood pressure is 100/72 mmHg. On presentation, the patient is visibly intoxicated with alcohol and cannot answer any questions. On physical examination, the oropharynx is dry, and breath sounds are decreased in the right lower lobe on pulmonary auscultation. Which pathogens are most likely responsible for this patient’s condition?  

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Alcoholism p. 595

Klebsiella in p. 143

Aspiration pneumonia

Klebsiella p. , 143

“Currant jelly” sputum

Klebsiella spp. p. 183

Currant jelly sputum p. 143, 183

Klebsiella pneumonia p. 716

Diabetes mellitus p. 352-360

Klebsiella p. , 143

Klebsiella spp. p. 143

alcoholism p. 176

currant jelly sputum p. 143, 183

Gram-negative algorithm p. 139

kidney stones p. 628

lactose fermentation p. 142

nosocomial infections p. 182

pneumonia p. NaN

taxonomy p. 122

urease-positive p. 125

urinary tract infections p. 625

Klebsiella pneumoniae

cephalosporins p. 186

encapsulation p. 125

immunodeficient patients p. 116

presentation p. 716

splenic dysfunction p. 96

UTIs caused by p. 179

Nosocomial infections p. 182, 280

Klebsiella p. , 143

Pneumonia p. 707

Klebsiella pneumoniae p. , 716

Urinary tract infections (UTIs) p. 179, 625

Klebsiella as cause p. 143


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.


Now, 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.


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.


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