Lower Susceptibility Breakpoints for the Enterobacteriaceae

Lower breakpoints for aztreonam and for several cephalosporins and carbapenems obviate the need for ESBL confirmatory testing or modified Hodge testing.

The minimum inhibitory concentrations (MICs) of cephalosporins and aztreonam for extended spectrum β-lactamase (ESBL)-producing Enterobacteriaceae can be elevated but still below the susceptibility breakpoint (BP). Previously, the Clinical and Laboratory Standards Institute (CLSI) recommended performing ESBL confirmatory testing on relevant bacterial species if MICs are high, and — for isolates that test positive — changing the interpretive result to “resistant” for penicillins, cephalosporins, and aztreonam. A similar approach was recommended to detect carbapenemase-producing Enterobacteriaceae using the modified Hodge test (JW Infect Dis Apr 8 2009).

Now, the CLSI has lowered the BPs of several cephalosporins, aztreonam, and the carbapenem…

Author

Daniel J. Diekema, MD, D(ABMM)