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Extended-Spectrum Beta-Lactamases (ESBLs) Review

  • Clinical and Laboratory Standards Institute (CLSI). Methods for Dilution Antimicrobial Susceptibility Tests for Bacteria That Grow Aerobically; Approved Standard; 10th ed. CLSI document M07-A10. Wayne, PA: January 2015.
  • Clinical and Laboratory Standards Institute (CLSI). Performance Standards for Antimicrobial Susceptibility Testing; 26th ed. CLSI document M100-S26. Wayne, PA: 2016.
It is important to detect ESBL-producing stains of Klebsiella pneumoniae, K. oxytoca, Escherichia. coli, and Proteus mirabilis as treatment failure may occur if the wrong cephalosporin is selected. These enzymes have the ability to 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.I
In January 2010, CLSI published revised cephalosporin (cefazolin, cefotaxime, ceftazidime, ceftizoxime, and ceftriaxone) and aztreonam interpretive criteria for Enterobacteriaceae:
  • The criteria for cefuroxime (parenteral) did not change.
  • Laboratories using the criteria detailed in the M100-S26 document, table 2A, published in 2016, no longer need to routinely test for extended-spectrum beta-lactamases (ESBLs) prior to reporting results.
  • IF using the criteria in M100-S26, table 2A, there is no longer a need to change the interpretive criteria for cephalosporin's, aztreonam or penicillin's from susceptible to resistant before reporting.
  • IF reporting moxalactam, cefonicid, cefamandole, or cefoperazone for E. coli, Klebsiella, or Proteus species, ESBL testing should be performed as outlined in CLSI document M100-S26, table 3A. If these isolates test ESBL positive, they should be reported as resistant. These drugs have limited availability in many countries, so the interpretive criteria were not evaluated by CLSI.
  • CLSI notes that ESBL testing could still be useful for epidemiology and infection control purposes.
  • ESBL testing should continue to be performed as described in M100-S26/table 3A, until the CLSI interpretive criteria outlined in M100-S26/table 2A is implemented.