Bacterium
Citrobacter species
Citrate-using enteric rods, E. coli mimics
SIT-roh-bak-ter
High-yield clue
Citrate-positive enteric rods that slowly ferment lactose and can mimic E. coli colonies, with C. freundii carrying inducible AmpC.
Overview
A group of Gram-negative enteric rods (e.g., C. freundii, C. koseri) named for citrate utilization; used in coursework as opportunistic pathogens that can resemble E. coli on lactose media.
Classification
- Gram-negative
- Rod
- Enterobacterales
- Facultative anaerobe
- Motile
Lab & identification clues
- Citrate utilization positive vocabulary
- Slow lactose fermentation on MacConkey
- Slow urea hydrolysis concept
- C. freundii inducible AmpC vocabulary
Associations
- Urinary tract infection study association
- Neonatal meningitis vocabulary (C. koseri)
- Healthcare-associated opportunist framing
Commonly confused with
- Escherichia coli
- Enterobacter cloacae
Frequently asked questions
What is Citrobacter species?
A group of Gram-negative enteric rods (e.g., C. freundii, C. koseri) named for citrate utilization; used in coursework as opportunistic pathogens that can resemble E. coli on lactose media.
What is the Gram stain of Citrobacter species?
Citrobacter species is Gram negative.
What are the lab clues for Citrobacter species?
Lab clues for Citrobacter species include Citrate utilization positive vocabulary, Slow lactose fermentation on MacConkey, Slow urea hydrolysis concept, and C. freundii inducible AmpC vocabulary.
What is Citrobacter species commonly confused with?
Citrobacter species is commonly confused with Escherichia coli and Enterobacter cloacae.
Original student-study summary. Sources checked: OpenStax Microbiology 2e, NCBI Bookshelf Medical Microbiology, and CDC topic pages where applicable; reviewed 2026-06. Educational only; no diagnosis, treatment, dosing, or specimen-handling guidance.