Gram-negative sepsis: Laboratory Identification

ESBL Activity

  • Illustrated is the picture of the surface of a disk diffusion test including a ceftazidime disk (left) and a combintation ceftazidime/clavulanic acid disk (right).
  • Observe in the photograph that the zone of inhibition around the the combination ceftazidime/clavulanic acid disk (right) is at least 5 mm larger than around the clavulanic acid disk (left).
  • This observation that the presence of clavulanic acid, a beta-lactamase inhibitor, has resulted in such a large increase in the zone of inhibition indicates that an extended spectrum beta lactamase (ESBL)is being produced.
  • When an organism is producing an ESBL, the susceptibility to individual cephalosporins cannot be predicted, thus requiring that each drug must be tested individually.
  • It may be important to detect ESBL-producing stains of K. pneumoniae and E. coli as treatment failure may occur if the wrong cephalosporin is selected.

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