Variability of Beta-Lactam Broth Microdilution for < em > Pseudomonas aeruginosa < /em >

Antimicrob Agents Chemother. 2021 Jul 26:AAC0064021. doi: 10.1128/AAC.00640-21. Online ahead of print.ABSTRACTAntimicrobial susceptibility testing for Pseudomonas aeruginosa is critical to determine suitable treatment options. Commercial susceptibility tests are typically calibrated against the reference method, broth microdilution (BMD). Imprecision of minimum inhibitory concentrations (MICs) obtained by BMD for the same isolate on repeat testing is known to exist. Factors that impact the extent of variability include concentration of the inoculum, operator effects, contents of the media, inherent strain properties, and the testing process or materials. We evaluated the variability of BMD for anti-pseudomonal beta-lactams (aztreonam, cefepime, ceftazidime, meropenem, piperacillin-tazobactam, ceftazidime-avibactam, ceftolozane-tazobactam) tested against a collection of P. aeruginosa isolates. Multiple replicate BMD tests were performed and MICs were compared to assess reproducibility, including the impact of the inoculum and operator. Overall, essential agreement (EA) was ≥ 90% for all beta-lactams tested. Absolute agreement (AA) was as low as 70% for some beta-lactams. Variability from the inoculum and operators impacted the reproducibility of MICs. Piperacillin-tazobactam exhibited the highest degree of variability with 74% AA and 94%% EA. The implications of MIC variability are extensive as the MIC is essential for multiple facets of microbiology, such as the development...
Source: Antimicrobial Agents and Chemotherapy - Category: Microbiology Authors: Source Type: research