Performance of disc diffusion and four commercially available MIC tests to determine mecillinam susceptibility on carbapenemase-producing Enterobacterales.

Urinary tract infections (UTIs) are predominantly caused by Enterobacterales, and escalating resistance poses significant challenges due to carbapenemase production, which can compromise the efficacy of last-resort antibiotics. Pivmecillinam, as the prodrug of mecillinam, may serve as a treatment option for UTIs caused by carbapenemase-producing Enterobacterales (CPE). However, accurate methods are required to accurately assess susceptibility to this antibiotic. This study aimed to evaluate the IMPORTANCE: The rising prevalence of carbapenemase-producing Enterobacterales (CPE) poses significant challenges to effective antibiotic therapy, particularly for urinary tract infections. Pivmecillinam, the prodrug of mecillinam, offers a promising treatment option due to its activity against certain carbapenemase-producing strains. However, selecting accurate susceptibility testing methods is crucial for ensuring appropriate clinical use. This study rigorously evaluates the performances of various susceptibility testing methods against a challenging collection of CPE isolates, identifying the strengths and limitations of each. By providing critical insights into their reliability, particularly for routine clinical settings, this research supports improved diagnostic accuracy and optimal use of mecillinam in combating multidrug-resistant infections. These findings are especially relevant as pivmecillinam gains international approval, underscoring its potential as a valuable alternative in the fight against antibiotic resistance.