Taxonomy
Family: Enterobacteriaceae

C. freundii complex
-- C. freundii, C. braakii, C. gilleni, C. murlinae, C. sedlakii, C. werkmanii, C. youngae
C. koseri (C. diversus)
C. amalonaticus
C. farmeri

Natural habitats
Isolated from soil, water, food, feces, urine of humans and animals.
They are commensals of the intestine.

The natural habitat of some Citrobacter species is unknown.

Clinical significance
Citrobacter species cause a wide variety of nosocomial infections, including infections of the respiratory- and urinary tract, blood, wounds, bone, meninges and other normally sterile tissues.

Especially patients which are hospitalized for more than 72 hours and neonates and immunocompromised patients are at risk for an infection caused by Citrobacter.

In many cases the infection arises from the gastrointestinal or genitourinary tract.