Carbapenem non-susceptibility overcalling by BD phoenix NMIC-500 panel

Area of Science:

• Clinical Microbiology
• Antimicrobial Resistance
• Diagnostic Accuracy

Background:

• Transitioning to the BD Phoenix system correlated with a reported decline in carbapenem susceptibility rates.
• Accurate determination of carbapenem susceptibility is critical for effective treatment of Enterobacterales infections.

Purpose of the Study:

• To evaluate the diagnostic accuracy of the BD Phoenix system for carbapenem susceptibility testing in Enterobacterales.
• To compare the performance of BD Phoenix against broth microdilution (BMD) and disk diffusion (DD) methods.

Main Methods:

• Collected 82 Enterobacterales isolates with reduced carbapenem susceptibility by BD Phoenix.
• Performed susceptibility testing using BD Phoenix, broth microdilution (BMD), and disk diffusion (DD) per CLSI guidelines.

Main Results:

• BD Phoenix showed significantly lower categorical agreement compared to BMD for ertapenem (58.8%) and imipenem (56.8%) versus DD (85.4%, 89.0%).
• BD Phoenix exhibited a tendency towards overcalling resistance, with major/minor error rates higher than DD.
• Disk diffusion demonstrated better accuracy, correctly categorizing most susceptible/intermediate results, though some resistant results were misclassified.

Conclusions:

• The BD Phoenix system may lead to overestimation of carbapenem non-susceptibility.
• Disk diffusion serves as a valuable complementary test to mitigate errors and improve accuracy.
• Implementing DD testing and providing interpretive comments can enhance clinical management of carbapenem-resistant infections.