Gram-Negative Resistance

Gram-Negative Resistance

Ambler Class A


  • Hydrolyzes penicillins and cephalosporins
  • Examples: CTX-M, KPC, SHV, TEM
  • Common bacteria: E. coli, Klebsiella, Enterobacteriaceae, Pseudomonas

Ambler Class B

Metallo-beta lactamases

  • Uses zinc for hydrolysis of beta-lactam ring
  • Examples: IMP, NDM, VIM
  • Common bacteria: Pseudomonas, Acinetobacter, Enterobacteriaceae

Ambler Class C


  • Hydrolyzes broad- and extended-spectrum cephalosporins
  • Example: AmpC
  • Common bacteria: Enterobacter, Citrobacter, Proteus, Serratia, Pseudomonas

Ambler Class D


  • Beta-lactamase production and reduced permeability or increased efflux
  • Example: OXA
  • Common bacteria: Acinetobacter, E. coli, Pseudomonas

Summary of Antibiotics with Extended Activity

Ambler Classes [*]Ceftazidime-Avibactam must be used in combination with aztreonam with Ambler Class B mutations

Pseudomonas and Acinetobacter Coverage

Additional Resources