Table 6.

Interpretive criteria giving best identification of β-lactamases

Speciesβ-Lactamase groupaPanelInterpretive criterion (−a)b% True positive% False positive% False negative
E. coli andK. pneumoniae AmpC/ESBLN+2CAZ ≥ 490010
CAZ, CTR, or CTX ≥ 49505
OtherCAZ, CTR, or CTX < 410050
AmpCCAZ ≥ 4 and CTT ≥ 888012
ESBLCAZ, CTR, or CTX ≥ 4 and CTT < 89525
AmpC/ESBLNU7CEPD ≥ 210000
OtherCEPD < 210000
AmpCCEPD ≥ 2 and FOX > 1610020
ESBLCEPD ≥ 2 and FOX ≤ 169703
K. oxytoca ESBLN+2CAZ ≥ 2c and CTR ≥ 4d 10000
High K1CAZ < 2 and CTR ≥ 410000
OtherCAZ < 2 and CTR < 410000
ESBLNU7CAZ > 1610000
High K1CAZ < 16 and CTR ≥ 810000
OtherCAZ < 16 and CTR < 810000
  • a See Table 1 for explanation of β-lactamase groups.

  • b Listed as concentration (in micrograms per milliliter) of antibiotic given. Abbreviations: CAZ, ceftazidime; CTR, ceftriaxone; CTX, cefotaxime; CTT, cefotetan; CEPD, cefpodoxime; FOX, cefoxitin.

  • c Cefotaxime or ceftizoxime (≥4 μg/ml) can be substituted for ceftazidime.

  • d Aztreonam (≥2 μg/ml) can be substituted for ceftriaxone.