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
Your notes
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.