Table 2.

A clinical approach to β-lactamases

Type of β-lactamase	Classic microorganisms or types	Clinical prescribing challenges
Extended-spectrum β-lactamases	Escherichia coli Klebsiella species Proteus species	Variability of in vitro activity consistently predicting in vivo efficacy Collateral damage of selection by certain antibiotic classes
AmpC	Serratia species Pseudomonas aeruginosa Indole + Proteus Citrobacter species Enterobacter species	Collateral benefit of possibly preventing selection of resistance by limiting antibiotics with activity against certain bacteria (as an example, pseudomonal-sparing antibiotic regimens)
Carbapenemases	KPC (Ambler Class A) NDM (Ambler Class B) Oxa-typea (Class D)	Selection risk by intensity and duration of prior antibiotic therapy Consideration of the role of combination therapy in treatment

^aMost characteristically found in Acinetobacter

KPC Klebsiella pneumoniae carbapenemase, NDM New Delhi metallo-β-lactamase (found in Enterobacteriaceae)