# Multicenter Analytical Performance Evaluation of the BD Phoenix NMIC-461 Panel for Carbapenemase Classification and Antimicrobial Susceptibility Testing of Enterobacterales, Pseudomonas aeruginosa, and Acinetobacter spp

## TL;DR

This study evaluates a new panel for detecting carbapenemase enzymes and antibiotic susceptibility in common bacteria, finding it effective but with some limitations in classification accuracy.

## Contribution

The study introduces and validates the BD Phoenix NMIC-461 panel for rapid carbapenemase classification and antimicrobial susceptibility testing in clinical isolates.

## Key findings

- The panel showed high sensitivity (98.8%) but moderate specificity (92.4%) for carbapenemase detection.
- AST performance was excellent with essential agreement over 95% for ten antimicrobial agents.
- Classification accuracy was reduced for Enterobacterales and Pseudomonas aeruginosa due to unclassified isolates.

## Abstract

Objectives: To evaluate the capability of the BD Phoenix NMIC-461 panel in the detection and classification of carbapenemase production and antimicrobial susceptibility testing of 10 antimicrobial agents among Enterobacterales, Pseudomonas aeruginosa, and Acinetobacter spp. Methods: A total of 714 non-repetitive clinical isolates from three tertiary hospitals in China were enrolled. Carbapenemase production was confirmed by the modified carbapenem inactivation method (mCIM), while carbapenemase typing was validated by polymerase chain reaction (PCR) and Sanger sequencing. Antimicrobial susceptibility testing (AST) for ten antimicrobial agents was performed using broth microdilution (BMD) as the reference method. Results: The sensitivity and specificity of carbapenemase detection were 98.8% (95% CI, 96.6–99.6) and 92.4% (95% CI, 89.5–94.6) separately compared to sequencing. Classification accuracy was compromised by carbapenemase-positive unclassified strains, particularly reducing sensitivity for Enterobacterales. Excluding unclassified strains, the sensitivity and specificity were: for class A, 100% (95% CI, 94.0–100) and 97.3% (95% CI, 95.6–98.4); for class B, 97.1% (95% CI, 89.7–99.2) and 97.6% (95% CI, 96.0–98.6); and for class D, 94.0% (95% CI, 87.9–97.3) and 99.1% (95% CI, 97.8–99.7). The panel was subject to limitations for carbapenemase detection when applied to Pseudomonas aeruginosa. The NMIC-461 panel demonstrated excellent performance for ten BMD-evaluated agents across four bacterial categories, with essential agreement (EA) exceeding 95% and category agreement (CA) exceeding 90% except for Levofloxacin, and major error (ME) and very major error (VME) rates below 3% and 1.5%, respectively. Conclusions: The BD Phoenix NMIC-461 panel provides reliable AST results for commonly encountered Gram-negative bacterial isolates. Regarding carbapenemase detection, the panel demonstrates high sensitivity but only moderate specificity in classifying carbapenemase-producing organisms (CPO), with a relatively high proportion of positive unclassified isolates among Enterobacterales and low specificity for P. aeruginosa. Overall, the implementation of NMIC-461 testing holds promise for significantly reducing turnaround time in both carbapenemase detection and classification.