# Evaluation of the Bruker MALDI Biotyper (MBT) subtyping module for detection of Klebsiella pneumoniae carbapenemase (KPC) in Enterobacterales in a Canadian clinical microbiology laboratory

## TL;DR

This study evaluates a MALDI-ToF tool's ability to detect KPC-producing Enterobacterales, finding it highly specific but with low sensitivity.

## Contribution

The study expands the validation of MALDI-ToF for KPC detection in a Canadian clinical setting with a diverse isolate collection.

## Key findings

- The MBT Module detected KPC with 100% specificity but only 15.5% sensitivity.
- It detected 40% of KPC-2 isolates but none of the KPC-3 isolates.
- A positive result reliably predicts KPC presence, but negative results are unreliable.

## Abstract

Early detection of Klebsiella pneumoniae carbapenemase (KPC)-producing Enterobacterales enables prompt initiation of appropriate antimicrobial therapy and infection prevention and control measures. The matrix-assisted laser desorption/ionization time-of-flight (MALDI-ToF) Biotyper (MBT) Subtyping Module (Bruker Daltonics) uses a characteristic spectral peak at ~11,109 m/z to identify KPC-producing Enterobacterales. The aim of this study was to assess the ability of the MBT Module to detect KPC among a variety of clinical and reference (AR Bank) Enterobacterales isolates. Detection of KPC was compared between the MBT Module and a laboratory-developed real-time KPC PCR. Of the 93 isolates tested, 58 (62.4%) were positive for KPC by PCR (39 clinical and 19 AR bank isolates), and 35 were negative. Among the KPC-positive PCR isolates, nine (seven clinical and two AR bank) also tested positive for KPC by the MBT Module. KPC detection via the MBT Module had a sensitivity of 15.5% and a specificity and positive predictive value of 100%. This study also assessed the performance of the MBT Module to detect KPC-2 versus KPC-3 among the AR Bank isolates. The MBT Module detected 2/5 (40.0%) KPC-2 and 0/14 of KPC-3 AR Bank isolates. As sensitivity was low, but specificity was high, a positive MBT Module result reliably predicts the presence of KPC; however, negative results cannot be relied upon to be truly KPC-negative.

Enterobacterales, a large order of pathogenic and commensal bacteria, can gain resistance to carbapenems through the acquisition of plasmids carrying genes, such as Klebsiella pneumoniae carbapenemase (KPC). Early detection of KPC is crucial for patient care; however, current detection methods that involve multiple time-consuming steps, commonly only undertaken after overnight susceptibility testing, indicate possible carbapenem resistance. This study examined the ability of matrix-assisted laser desorption/ionization time-of-flight (MALDI-ToF), a common diagnostic tool in the clinical laboratory, to detect KPC among Enterobacterales. KPC detection via MALDI-ToF had low sensitivity but 100% specificity. These results support and expand the microbiological and geographical range of prior publications for this tool. A practical application of this highly specific method would involve rapid triaging of KPC-positive isolates a day earlier than current methods, permitting initiation of more timely therapeutic and infection prevention and control measures.