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Citrobacter species

Background:

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Enterobacteriaceae  (Gram Negative Bacilli)  
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>Citrobacter species: led
     1] Citrobacter koseri
     2] Citrobacter freundii
>Enterobacter species
     1] Enterobacter cloacae,
     2] Enterobacter aerogenes)
>Escherichia coli
>Klebsiella species:
     1] Klebsiella ozaenae
     2] Klebsiella pneumoniae
     3] Klebsiella rhinoscleromatis
>Morganella species 
     1] (Morganella morganii)
>Proteus species:
     1] Proteus mirabilis
     2] Proteus vulgaris
>Providencia species:
     1] Providencia_rettgeri
     2] Providencia stuartii
>Salmonella species:
     1] Salmonella enteritidis
     2] Salmonella typhi
     3] Other
>Serratia marcescens
>Shigella species:  
     1] Shigella dysenteriae (serogroup A)
     2] Shigella flexneri
     3] Shigella boydii
     4] Shigella sonnei
     5] Other

Citrobacter:

  • Gram-negative coliform bacteria in the Enterobacteriaceae family. Citrobacter species are differentiated by their ability to convert tryptophan to indole, ferment lactose, and use malonate.
  • The species C. amalonaticus, C. koseri, and C. freundii can use citrate as a sole carbon source.
  • Ubiquitous: found almost everywhere in soil, water, wastewater, etc. Also found in the human intestine.
  • Rarely the source of illnesses, except for infections of the urinary tract and infant meningitis and sepsis.
  • C. freundii strains have inducible ampC genes encoding resistance to ampicillin and first-generation cephalosporins. In addition, isolates of Citrobacter may be resistant to many other antibiotics as a result of plasmid-encoded resistance genes.

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Therapy:

Important considerations:  The choice of an agent should be based on local antimicrobial sensitivities, site of infection, cost, and comorbid conditions.   Generally, the most common agents/regimens are listed first.   Listed dosages may need to be adjusted for renal dysfunction.  

Citrobacter is usually resistant to multiple antibiotics due to plasmid-encoded resistance genes.

  1. Cefpodoxime (Vantin ®) 200-400 mg orally twice daily   [3rd generation ceph]
  2. Ceftriaxone 1-2 grams IV q24h  (range: 1-2 grams q12-24h)
  3. Ciprofloxacin  400mg IV q12h (Severe/complicated: 400mg IV q8h)
  4. Cefepime 1-2 grams IV every 8-12 hours
  5. Imipenem 500mg IV every 6 hours [Range: 250-1000 mg q6-8h]
  6. Meropenem 1 gram IV q8h
  7. Doripenem 500 mg IV q8h

Citrobacter species