Serratia marcescens- Bacterial strain, organism, antimicrobial therapy
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Serratia marcescens

Background:

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Enterobacteriaceae  (Gram Negative Bacilli)  
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>Citrobacter species:
     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 led
>Shigella species:  
     1] Shigella dysenteriae (serogroup A)
     2] Shigella flexneri
     3] Shigella boydii
     4] Shigella sonnei
     5] Other




Serratia marcescens
  • Gram-negative, motile, and rod-shaped bacterium in the family Enterobacteriaceae.
  • It is differentiated from other Gram-negative bacteria by its ability to perform casein hydrolysis, which allows it to produce extracellular metalloproteinases which are believed to function in cell-to-extracellular matrix interactions. S. marcescens also exhibits tryptophan and citrate degradation.
  • Another determination of S. marcescens is its capability to produce lactic acid via oxidative and fermentative metabolism. Therefore, it is said that S. marcescens is lactic acid O/F+.
  • Human pathogen involved in nosocomial infections, particularly catheter-associated bacteremia, urinary tract infections and wound infections, and is responsible for 1.4% of nosocomial bacteremia cases in the United States.
  • It is commonly found in the respiratory and urinary tracts of hospitalized adults and in the gastrointestinal system of children.
  • Ubiquitous presence in the environment with a preference for damp conditions.  Commonly found growing in bathrooms (especially on tile grout, shower corners, toilet water line, and basin), where it manifests as a pink discoloration and slimy film.
  • S. marcescens can cause infection in several sites, including the urinary tract, respiratory tract, wounds, and the eye, where it may cause conjunctivitis, keratitis, endophthalmitis, and tear duct infections. It is also a rare cause of endocarditis and osteomyelitis (particularly in people who use intravenous drugs recreationally), pneumonia, and meningitis.
  • Most S. marcescens strains are resistant to several antibiotics because of the presence of R-factors, which are a type of plasmid that carry one or more genes that encode resistance; all are considered intrinsically resistant to ampicillin, macrolides, and first-generation cephalosporins (such as cephalexin).

 



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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.  
  1. Ciprofloxacin 500-750 mg orally q12h or 400mg IV q12h
  2. Levofloxacin 500mg - 750 mg IV/PO once daily
  3. Piperacillin-tazobactam (Zosyn ®)  3.375 grams IV q6h
  4. Aminoglycoside:  Gentamicin, Tobramycin, or Amikacin
  5. Aztreonam: 1-2 grams IV q8-12h.  Severe/Life-threatening: 2 grams IV q6-8h.
  6. Meropenem 0.5 - 1 gram IV q8h
  7. Imipenem 500mg IV every 6 hours [Range: 250-1000 mg q6-8h]

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