Evaluation of commercial susceptibility testing methods for <i>in vitro</i> determining daptomycin susceptibility in vancomycin-resistant <i>Enterococcus faecium</i>

Vancomycin-resistant <i>Enterococcus faecium</i> (VR<i>Efm</i>) is a major cause of hospital-acquired infections worldwide, posing a serious threat to patient safety and infection control. Daptomycin remains one of the few therapeutic options for severe VR<i>Efm</i> infections, yet its efficacy depends on accurately determining bacterial susceptibility. Even small variations in measured minimum inhibitory concentrations can influence treatment success or failure. In this study, we systematically evaluated several commercial antimicrobial susceptibility testing methods for daptomycin against VR<i>Efm</i> and compared them with the reference broth microdilution (BMD) method. Our results show that many commonly used systems underestimate resistance, particularly for isolates near the clinical breakpoint. This underestimation may lead to inappropriate treatment decisions. The study provides evidence-based recommendations for clinical laboratories and emphasizes the importance of confirmatory BMD testing to ensure reliable results, optimize patient management, and prevent the further spread of antimicrobial resistance.