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Infectious Disease Antimicrobial Resistance Advanced
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AmpC Beta-Lactamase Organisms: SPACE

S
P
A
C
E
Gram-negative bacterial pathogens possessing inducible chromosomal AmpC beta-lactamases that develop resistance to cephalosporins during therapy.

These organisms harbor inducible ampC genes. Exposure to 3rd-generation cephalosporins (e.g. ceftriaxone) selects for derepressed mutants that hyperproduce AmpC enzymes, leading to treatment failure despite in vitro initial susceptibility.

Systematic Breakdown

S

Serratia marcescens

Gram-negative bacillus known for red pigment (prodigiosin); hospital-acquired UTI and pneumonia.

P

Pseudomonas aeruginosa / Proteus (indole-positive)

Opportunistic pathogen; high baseline resistance profile (Proteus vulgaris).

A

Acinetobacter baumannii

Critical ICU threat; rapidly acquires extensive multi-drug resistance.

C

Citrobacter freundii

Common biliary and urinary pathogen; high risk of AmpC derepression during therapy.

E

Enterobacter cloacae

Most classic clinical offender; routinely fails Ceftriaxone monotherapy in bacteremia.

High-Yield Clinical Pearls & Exam Tips
  • Golden Antibiotic Rule: Do NOT treat systemic invasive infections caused by SPACE organisms with Ceftriaxone, even if the lab report says 'Susceptible'!
  • Drug of choice: Cefepime (4th-gen cephalosporin, stable against AmpC) or a Carbapenem (Meropenem).
Related Pharmaceuticals
Cefepime Meropenem Piperacillin-Tazobactam Ceftriaxone
Related Clinical Conditions
Ventilator-Associated Pneumonia Catheter-Associated UTI Gram-Negative Bacteremia
Authoritative Sources: IDSA Guidance on Treatment of Antimicrobial-Resistant Gram-Negative Infections · Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases

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System Notice

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