Citrobacter

# Overview
Citrobacter is a genus of Gram-negative coliform bacteria in the Enterobacteriaceae family. They are rarely the source of illnesses, except for infections of the urinary tract and infant meningitis and sepsis.

# Organism
- Citrobacter is a genus of gram-negative Coliform bacteria in the Enterobacteriaceae family.
- The species C. amalonaticus, C. koseri, and C. freundii use solely citrate as a carbon source. These bacteria can be found almost everywhere in soil, water, wastewater, etc. It can also be found in the human intestine. They are rarely the source of illnesses, except for infections of the urinary tract and infant meningitis.
- Citrobacter shows the ability to accumulate uranium by building phosphate complexes.

## Citrobacter freundi
- Citrobacter freundi is a species of facultative. aerobic. Gram-negative bacilli of the Enterobacteriaceae family. The bacteria are long rod-shaped with a typical length of 15 m. Most C. freundii cells are surrounded by several flagella used for locomotion, but a few are not mobile. It can be found in soil, water, sewage, food, and the intestinal tracts of animals and humans. The Citrobacter genus was discovered in 1932 by Werkman and Gillen. Cultures of C. freundii were isolated and identified in the same year from soil extracts.
- As an opportunistic pathogen, C. freundii is responsible for a number of significant infections. It is known to be the cause of a number of nosocomial infections of the respiratory tract, urinary tract, blood, and many other normally sterile sites in patients. C. freundii represents about 29% of all opportunistic infections.
- Surprisingly, this infectious microbe in humans plays a positive role in the environment. C. freundii is responsible for reducing nitrate to nitrite in the environment. This conversion is an important and crucial stage in the nitrogen cycle. These bacteria also help in recycling nitrogen.
- C. freundii has also been investigated for biodegradation of tannic acid used in tanneries.
- For metabolism, C. freundii has an ability to grow on glycerol as the sole carbon and energy source. Within its cell, a bacterial microcompartment can be found, which is capable of processing propanediol.

## Antimicrobial regimen
- Citrobacter freundii
- Preferred regimen (1): Meropenem 1-2 g IV q8h
- Preferred regimen (2): Imipenem 1 g IV q6h
- Preferred regimen (3): Doripenem 500 mg IV q8h
- Preferred regimen (4): Cefepime 1-2 g IV q8h
- Preferred regimen (5): Ciprofloxacin 400 mg IV q12h or 500 mg PO bid for UTI
- Preferred regimen (6): Gentamicin 5 mg/kg IV q24h
- Alternative regimen (1): Piperacillin-tazobactam 3.375 mg IV q6h
- Alternative regimen (2): Aztreonam 1-2 g IV q6h
- Alternative regimen (3): TMP-SMX 5 mg/kg q6h IV or DS PO bid for UTI
- Note: Usually Carbenicillin sensitive, Cephalothin resistant
- Citrobacter koseri
- Preferred regimen (1): Ceftriaxone 1-2 g IV q12-24h
- Preferred regimen (2): Cefotaxime 1-2 g IV q6h
- Preferred regimen (3): Cefepime 1-2 IV q8h
- Alternative regimen (1): Ciprofloxacin 400 mg IV q12h or 500 mg PO q12h for UTI
- Alternative regimen (2): Imipenem 1 g IV q6h
- Alternative regimen (3): Doripenem 500 mg IV q8h
- Alternative regimen (4): Meropenem 1-2 g IV q8h
- Alternative regimen (5): Aztreonam 1-2 g IV q6h
- Alternative regimen (6): TMP-SMX 5 mg/kg IV q6h  or DS PO bid for UTI
- Note: Usually Ampicillin resistant, but may be sensitive to first generation cephalosporins.

# Gallery
- Triple sugar iron agar (TSI) tested for Salmonella (H2S+) and (H2S-); Citrobacter sp. and S. arizonae. From Public Health Image Library (PHIL).