SPICE organisms

First topic at hand is SPICE organisms. These are the organisms that appear to be sensitive to many antibiotics, but once they are exposed to certain antibiotics (ex. 3rd generation cephalosporins), they quickly develop resistance to them.

SPICE stands for:

S: Serratia spp.

P: Providencia

I: “indole-positive” Proteus spp. (this includes: P. vulgaris) *NOT P.mirabilis

C: Citrobacter spp.

E: Enterobacter spp.

*There are other, less known bacteria included in this group (Cronobacter, Edwardsiella, Hafnia, Morganella, Aeromonas)

 

*[Organisms like Pseudomonas and Acinetobacter produce AmpC gene normally – which is why they have intrinsic resistance to 3rd generation cephalosporins and do not technically fall into the AmpC inducer SPICE group.]

 

The SPICE pathogens can be induced to produce an AmpC beta-lactamase gene that encodes an enzyme that cleaves the beta-lactam group in the antibiotic and renders it inactive.

 

This gene may not be detected initially (low level of expression of the gene) but may appear (induced to express higher levels of gene) after a period of exposure to beta-lactam antibiotics.

(Clinical translation: Initially they will appear susceptible to beta-lactams, but eventually will develop resistance to them. *tricky little bastards, aren’t they?)

 

Once beta-lactam is removed, the AmpC gene production is reduced once more and the pathogens will appear sensitive to 3rd generation cephalosporins and penicillins again. .

 

Resistance develops anywhere from 24h to 2-3 weeks.

 

Clinical relevance:

  • If the course of antibiotics is short or if the antibiotic can easily overcome the MIC concentration needed for bacterial killing, then the risk of inducing AmpC gene production is low
    • Clinical examples (~<1 week duration of antibiotics):
      • UTI
      • Pneumonia
  • Short course for intra-abdominal infectionHowever, this becomes an issue in areas where antibiotics have difficulty penetrating (because it is less likely to overcome the MIC concentration needed) or when antibiotics are needed to be given over a longer period of time.
    • Clinical examples:
      • Endocarditis
      • Bacteremia
      • Osteomyelitis
      • Septic arthritis
      • Abscesses

 

Antibiotics to avoid:

  • Penicillin class (including piperacillin-tazobactam)
  • Most cephalosporins (1st, 2nd, and 3rd generation)

 

Antibiotics to use:

  • 4th generation cephalosporins (i.e. cefepime at higher doses, q8h)
  • Carbapenems
  • Aminoglycosides
  • Fluoroquinolones

TAKE-HOME POINTS:

  1. Remember the members of the SPICE group
  2. You may be successful in treating an infection in short courses of therapy or in infections where antibiotic penetration is high. But in patients with bacteremia, bone, joint, or valve infections – strongly consider 4th generation cephalosporin or a carbapenem.

 

 

Have a question, comment, or a suggestion for a future blog post? Post your comment below!

 

 

References:

  • http://m.antimicrobialstewardship.com/clinical_summaries/index.php?page=esbl_and_spice
  • Jacoby, G.A. AmpC beta-lactamases. Clinical Microbiology Review. 2009. 22(1):161-182. doi: 10.1128/CMR.00036-08
  • Harris, P.N.A, and Ferguson, J.K. Antibiotic therapy for inducible AmpC beta-lactamase-producing Gram-negative bacilli: what are the lternatives to carbapenems, quinolones, and aminoglycosides? 2012. International Journal of Antimicrobial Agents, 40: 297-305.

 

 

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