Focused Commentary; About Revision of CLSI Antimicrobial Breakpoints, 2018-2021

and limitations of new breakpoints with a review of large study data. In addition, I reviewed problems associated with each antimicrobial breakpoint and made suggestions for how they might be improved, for example, increasing or decreasing the minimum inhibitory concentration (MIC) or zone diameter, deleting or adding an S, I, or R category, introducing new concepts (such as susceptible-dose dependent (SDD)), and requesting more evaluation methods. Conclusions; CLSI annually publishes guidelines for antimicrobial resistance tests. I reviewed problems associated with each antimicrobial breakpoint for last 4 years, and made suggestions for how they might be improved. limitations pneumoniae , by whole genome sequencing. With increased MICs, monitoring of this horizontally transferable gene and breakpoint reevaluation in isolates, including isolates with MICs greater than 0.25 μg/mL , are needed. The clinical association with this transferable gene is also needed to be evaluated on a larger cohort. ceftolozane/tazobactam, meropenem/vaborbactam and imipenem/relebactam inhibit ESBL, CRE or CRPA. Avibactam or vaborbactam reduces the MIC of β-lactam drugs by several fold, showing an effect on ESBL, AmpC, or KPC; however, it has no effect on metallo-β-lactamase, oxa-type β-lactamase, or resistance to porin mutation (38). As an antimicrobial resistance detection method, the disk diffusion method of ceftazidime/avibactam or imipenem/relebactam has low categorical agreement compared to reference broth microdilution in CRE isolates and it overcalls resistance (39-41). Therefore, reevaluation of the disk diffusion method is required. The E-test of imipenem/relebactam categorical agreement was > 90%; however, the E-test showed a one-grade high MIC result. Therefore, isolates with an E-test MIC of 2–4 μg/mL should be retested with broth microdilution to reduce major or minor errors. The resistance to β-lactam combination agents is transferred by conjugation, with the possibility of horizontal transfer of low-level resistance in CRE and CRPA, and the resistance mechanism of β-lactam combination agents should be detected using whole genome sequencing.