Comparison of Carbapenem Minimum Inhibitory Concentrations of Oxacillin-48-like Klebsiella Pneumoniae by Sensititre, Vitek 2, MicroScan, and Etest.

Objectives: The aim of this laboratory-based study was to compare carbapenem MICs yielded by Sensititre, Vitek 2, MicroScan WalkAway plus and Etest for Oxacillin (OXA)-48-like Klebsiella pneumoniae isolates. Methods: Analysis was performed for categorical agreement for ertapenem, meropenem, and imipenem, and the proportion of isolates with MICs <= 8mg/mL and the MIC50/MIC90 for meropenem and imipenem, from a convenience sample of 82 deduplicated blood culture OXA-48-like K. pneumoniae isolates. Results: The proportion of isolates testing susceptible to ertapenem by Etest (19/82, 23.1%) differed from Sensititre/Vitek (0/82) and MicroScan (2/82, 2.4%) (p < 0.001 for all). For meropenem, the proportion of isolates susceptible by Etest (31/82, 37.8%) differed from Sensititre/Vitek (16/82, 19.5%) (p - 0.015). There was variation in the proportion of isolates that tested imipenem susceptible when comparing Sensititre (9/82, 11%) and Vitek (8/82, 9.8%) to MicroScan (27/82, 32.9%), p - 0.001 and p < 0.001, respectively, Sensititre and Vitek to Etest (45/ 82, 54.9%), p < 0.001 for both, and MicroScan to Etest, p - 0.007. The proportion of isolates with meropenem MICs <= 8mg/mL with Sensititre and Vitek differed significantly from Etest, 58.5% and 85.4%, respectively, p < 0.001. A 2-fold difference between the Sensititre and Vitek meropenem and imipenem MIC at which >= 50% of isolates were inhibited compared to the MicroScan, and a 4-fold difference compared to Etest, was present. Conclusions: Substantial variability in carbapenem MICs for OXA-48-like carbapenemase-producing Enterobacterales isolates by the four methods was demonstrated. Performance characteristics verification of MIC methods in use for the predominant carbapenemase-producing Enterobacterales type is required by laboratories to optimize the accuracy of carbapenem reporting. Trusha Nana, Clin Microbiol Infect 2022;28:1650.e1e1650.e5