What is the clinical relevance of “SPICE” organisms?

 

“SPICE” stands for the following bacterial species: Serratia, Pseudomonas, indole-positive Proteae (e.g. Proteus sp. [not mirabilis], Providencia, Morganella), Citrobacter, and Enterobacter.

These organisms (as well as Acinetobacter sp.) often have inducible chromosomal AmpC ß-lactamase genes that may be derepressed during therapy, conferring in vivo ß-lactam resistance despite apparent sensitivity in vitro (1,2). Because AmpC genes in clinical isolates are not routinely screened for in the laboratory, the following treatment approach to these organisms is often adopted (1).

Third generation cephalosporins (e.g. ceftriaxone and ceftazidime) are usually avoided irrespective of in vitro susceptibility. For less serious infections (e.g. urinary tract infections) or severe infections in carefully monitored clinically stable patients, piperacillin-tazobactam and cefepime in particular may be used due to their lower risk of induced resistance. For severe infections (e.g. pneumonia and bacteremia) in seriously ill patients, carbapenems (e.g. meropenem, imipenem-cilastatin) are often the drugs of choice.  Fluroroquinolones and aminoglycosides may also be considered.

References

  1. MacDougall C. Beyond susceptible and resistant, part I: treatment of infections due to Gram-negative organisms with inducible ß-lactamases. J Pediatr Pharmacol Ther 2011;16:23-30.
  2. Jacoby GA. AmpC ß-lactamases. Clin Microbiol Rev 2009;22:161-182.

Contributed by Avi Geller, 3rd year Medical Student, Harvard Medical School

What is the clinical relevance of “SPICE” organisms?

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