It is important to detect ESBL-producing strains of Klebsiella pneumoniae, K. oxytoca, Escherichia coli, and Proteus mirabilis, as treatment failure may occur if the wrong cephalosporin is selected. These enzymes can hydrolyze third-generation cephalosporins and aztreonam but are inhibited by clavulanic acid. ESBL-producing organisms can also exhibit co-resistance to many other classes of antibiotics.
When using current CLSI breakpoints for the Enterobacterales, routine ESBL testing is no longer necessary before reporting results (meaning, it is no longer required to edit results for cephalosporins, aztreonam, or penicillins from susceptible to resistant). However, the ESBL test might be useful in epidemiologic studies. (Some molecular assays are available, and an ESBL-type target is used.) If current breakpoints have been implemented, report interpretations as usual.
Note: Breakpoints for drugs with limited availability in many countries (e.g., moxalactam, cefonicid, cefamandole, and cefoperazone) have not been evaluated. If considering the use of these drugs for isolates of E. coli, Klebsiella species, or Proteus species, ESBL testing should be performed—and if positive, these drugs should be reported as resistant.
