Question 25.2

56 year old man presents with pyelonephritis. Ultrasound reveals an obstructed right kidney. Percutaneous nephrostomy is performed.

Blood cultures: 2/2 bottles growing Enterobacter cloacae, sensitive to ceftriaxone

Pus from renal pelvis: Gram negative bacillus on microscopy. Cultures growing Enterobacter cloacae, sensitive to ceftriaxone, aminoglycoside, meropenem

What antibiotic will you choose and why?

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College Answer

Choose an aminoglycoside or meropenem because it is an ESCAPM organism. (develop resistance to third gen cephalosporins)


More correctly, the ESCAPPM organisms are:

  • Enterobacter
  • Serratia
  • Citrobacrter
  • Acinetobacter (and Aeromonas)
  • Proteus
  • Providencia
  • Morganella

These are Gram-negative organisms with induceable chromosomal AmpC cephalosporinase/β-lactamase enzymes. Resistance to β-lactams and cephalosprins develops quickly in these species. The linked article on this topic also identifies Chromobacterium violaceum,  EnterobacterE. coliHafnia alvei, Lysobacter lactamgenusOchrobactrum anthropiProteus rettgeri,  Pseudomonas aeruginosaPsychrobacter immobilis, Rhodobacter sphaeroides and Yersinia enterocolitica as carriers of the AmpC β-lactamase.

ESCAPPM and HACEK bacteria are discussed elsewhere in the Required Reading section.

If one does not wish to deal with the emergeance of resistance midway though the course of antibiotics, one will choose an aminoglycoside or carbapenem for this purpose.


BOYLE, ROBERT J., et al. "Clinical implications of inducible beta-lactamase activity in Gram-negative bacteremia in children." The Pediatric infectious disease journal 21.10 (2002): 935-939.


Sfakinos, John. "Detecting the dual presence of AmpC and ESBL enzymes."Microbiology Australia 30.5 (2009): 208-209.


Philippon, Alain, Guillaume Arlet, and George A. Jacoby. "Plasmid-determined AmpC-type β-lactamases." Antimicrobial agents and chemotherapy 46.1 (2002): 1-11.