Klebsiella pneumoniae

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.

Characteristics

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.

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.