Carbapenemase production is another resistance mechanism of the Enterobacterales order (and also applicable to Pseudomonas aeruginosa). Infection prevention or epidemiologic investigations may require identification of these organisms. Patients identified as harboring these generally pan-resistant strains should be isolated to prevent spread among other compromised individuals. These multi-drug resistant organisms (MDROs) are challenging to treat.
Testing not susceptible to ertapenem is usually the most sensitive indicator of carbapenemase production; the organism also typically tests resistant to one or more cephalosporins subclass III (e.g., cefoperazone, cefotaxime, ceftazidime, ceftizoxime, ceftriaxone). Additional tests should be performed if laboratories still use CLSI 2010 M100 MIC breakpoints.
When isolates of Enterobacterales are suspicious for production based on imipenem, meropenem, or ertapenem results, test the isolates using supplemental tests such as CarbaNP test, mCIM, eCIM, and/or a molecular assay, per CLSI. After the lab implements the current CLSI breakpoints, these additional tests may not need to be performed (unless for epidemiologic purposes). Carbapenem results would no longer need to be edited to "resistant" based on the results of the additional tests.
