Klebsiella aerogenes

(Previously Enterobacter aerogenes)

Gram Stain

• Gram negative bacilli - fermenter

Clinical Significance

This organism is an opportunistic pathogen which rarely causes primary infections in healthy individuals. 

It is a frequent colonizer in hospitalized patients, especially those who have received broad-spectrum antibiotics. 

K. aerogenes has been associated with a variety of nosocomial infections in debilitated/ immunocompromised individuals. 

Infections include respiratory and urinary tract infections, wound/ulcer infections (especially burns), osteomyelitis, meningitis, bacteremia, and endocarditis. 

Bacteremia with this organism is often polymicrobial.

Usual Susceptibility Pattern

This organism produces a chromosomally mediated inducible cephalosporinase (AmpC) and is resistant to penicillins and 1st/2nd generation cephalosporins.

Although they often exhibit in vitro susceptibility to 3rd generation cephalosporins, use of these agents may result in selection of resistant strains. 

The beta-lactamase produced by these organisms is not inhibited by beta-lactamase inhibitors and as such, beta-lactamase inhibitor combinations are not recommended.

K. aerogenes is usually susceptible to aminoglycosides, quinolones, and TMP/SMX.

Susceptibility to fosfomycin is variable.

The majority are resistant to nitrofurantoin.