Extended-spectrum β-lactamases

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(Redirected from ESBLs)

Background

Identification

Screening for ESBL production
Bacterium Antibiotic Disc Diffusion Broth Microdilution
Klebsiella pneumoniae, Klebsiella oxytoca, and Escherichia coli cefpodoxime ≤17 mm ≥8 μg/mL
ceftazidime ≤22 mm ≥2 μg/mL
aztreonam ≤27 mm ≥2 μg/mL
cefotaxime ≤27 mm ≥2 μg/mL
ceftriaxone ≤25 mm ≥2 μg/mL
Proteus mirabilis cefpodoxime ≤22 mm ≥2 μg/mL
ceftazidime ≤22 mm ≥2 μg/mL
cefotaxime ≤27 mm ≥2 μg/mL
  • Organisms that screen positive have further testing to determine the presence of an ESBL
  • Class A, for all organisms that screen positive,
  • Class B, for organisms that are also resistant to carbapenems
  • Class C, for organisms that are non-susceptible to cefoxitin
    • A double-disc diffusion method is used to test if the results for cefoxitin are attenuated by cloxacillin (that is, if the isolate becomes even more susceptible)
    • An increase in the zone of ≥4 mm is positive for AmpC (Class C ESBL) phenotype
  • Class D, difficult to identify with phenotypic testing

Management