Citrobacter koseri

Gram Stain

• Gram negative bacilli - fermenter

Clinical Significance

This organism is found in the gastrointestinal tract of humans and animals.

It is a cause of urinary tract infections, bacteremia, skin/soft tissue and bone infections. 

It is associated with central nervous system (CNS) infections in neonates (< 2 months) including meningitis, ventriculitis, and brain abscesses.

Usual Susceptibility Pattern

This organism produces a chromosomal penicillinase rendering it resistant to ampicillin and cephalexin.  Hyperproduction of this enzyme can result in resistance to cefazolin.  Amoxicillin-clavulanate, piperacillin-tazobactam, and 3rd generation cephalosporins may be affected.