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The shift from “MIC-Only” back to carbapenemase testing among carbapenem-resistant Enterobacterales: what clinical laboratories need to know about updated CLSI guidance | Journal of Clinical Microbiology
Carbapenem-resistant organisms (CROs) are a critical public health concern worldwide due to increasing prevalence and limited therapeutic options (1, 2). This group includes all gram-negative organisms resistant to any carbapenem tested, as appropriate for the specific organism (e.g., ertapenem is not evaluated for the glucose-non-fermenters as they are intrinsically resistant). Within this group, carbapenemase-producing (CP) carbapenem-resistant organisms (CP-CROs) are especially worrisome as carbapenemases inactivate most β-lactams and spread efficiently via mobile genetic elements (e.g., plasmids) driving carbapenem resistance among Gram-negative organisms. CP-CRO, including Enterobacterales, Pseudomonas aeruginosa, and Acinetobacter baumannii complex, pose the greatest therapeutic and epidemiological challenge (3). Over the last decade, many changes have occurred, resulting in the necessity for clinical laboratories to perform carbapenemase testing to inform patient management. These changes include (i) the increasing prevalence and changing epidemiology of carbapenemases, (ii) the availability of novel beta-lactam combination agents with specificity to targeted carbapenemases, (iii) the emphasis on antimicrobial stewardship and preservation of agents to reduce the emergence of antimicrobial resistance, and (iv) the availability of novel diagnostics to more rapidly detect certain antimicrobial resistance genes to guide therapeutic management. The focus of this minireview will be on recent Clinical and Laboratory Standards Institute (CLSI) changes to the guidance for carbapenemase testing among carbapenem-resistant Enterobacterales (CRE).
