SPICE organisms

Background

• Gram-negative bacteria with inducible or derepressable beta-lactamases, primarily AmpC β-lactamase

Organisms

• Serratia
• Providencia
• Indole-positive Proteus (e.g. Proteus vulgaris, but not Proteus mirabilis)
• Citrobacter species
  • C. koseri does not have an AmpC
• Enterobacter cloacae, and now also Klebsiella aerogenes (previously Enterobacter aerogenes)

Also:

• Hafnia alvei
• Acinetobacter, though not inducible or AmpC (merely very resistant_
• Morganella morganii
• Cronobacter
• Edwardsiella

Management

• For Enterobacter cloacae, Klebsiella aerogenes, and Citrobacter freundii, avoid all penicillins and cephalosporins regardless of susceptibility testing
  • Carbapenems still work, as do aminoglycosides
  • Cefipime still works when MIC ≤2 mcg/mL
• For Serratia marcescens, Morganella morganii, and Providencia, treat based on susceptibility testing
• Less data for Hafnia alvei, Citrobacter youngae, and Yersinia enterocolitica, but reasonable to treat based on susceptibility testing

Further Reading

• Jones R, Baquero F, Privitera G, Inoue M, Widermann B. Inducible β-lactamase-mediated resistance to third-generation cephalosporins. Clin Microbio Infect. 1997;3(1):S7-S20.
• https://academic.oup.com/cid/advance-article/doi/10.1093/cid/ciz173/5369903