# Assessment of the Diagnostic Accuracy of the Modified Hodge Test and Modified Carbapenem Inactivation Method for Identifying Carbapenem Resistance Mechanisms in Klebsiella pneumoniae: A Whole Genome Sequencing-Based Exploratory Study

## TL;DR

This study evaluates how well two tests, MHT and mCIM, detect carbapenem resistance in Klebsiella pneumoniae using whole genome sequencing for validation.

## Contribution

The study provides a whole-genome sequencing-based evaluation of the diagnostic accuracy of MHT and mCIM for detecting carbapenem resistance mechanisms in Klebsiella pneumoniae.

## Key findings

- MHT showed high specificity but low sensitivity for detecting carbapenemase genes.
- mCIM had very low sensitivity and no significant agreement with PCR for carbapenemase detection.
- PCR and WGS results were concordant in identifying resistance genes.

## Abstract

Aim: Carbapenem-resistant Klebsiella pneumoniae (CRKP) is a major public health concern, particularly in immunocompromised and critically ill patients. Colistin and tigecycline are among the last-resort treatment options, while the primary driver of CRKP emergence is carbapenemase production, especially Klebsiella pneumoniae carbapenemase (KPC) and metallo-β-lactamase (MBL). A thorough understanding of its resistance mechanisms is essential for selecting the most effective antimicrobial therapy. This study aimed to evaluate the diagnostic accuracy of the modified Hodge test (MHT) and modified carbapenem inactivation method (mCIM) in detecting molecular resistance mechanisms in CRKP clinical isolates.

Material and methods: This exploratory study consisted of 65 CRKP isolates, which were identified using matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) (Bruker Daltonik GmbH, Bremen, Germany). Antimicrobial susceptibility testing was performed using the BD Phoenix system. The test isolates were subjected to MHT and mCIM and later shipped to the Central Research Laboratory (CRL), Bengaluru, India, where they were subjected to polymerase chain reaction (PCR) and whole-genome sequencing (WGS).

Results: PCR detected blaOXA-48-like, blaNDM-1, blaNDM-5, and blaKPC genes in 79.7%, 10.2%, 64.4%, and 1.7% CRKP isolates, respectively. The PCR results were concordant with WGS. The MHT demonstrated an overall sensitivity of 60.3%, specificity of 100%, positive predictive value (PPV) of 100%, and negative predictive value (NPV) of 4.2% for detecting carbapenemase production. It showed the highest sensitivity and specificity for blaKPC (100%) and blaOXA-48-like (75%) genes, respectively, with the highest PPV for blaOXA-48-like (91.4%) and NPV for blaKPC (100%). However, agreement between MHT and PCR for carbapenemase detection was negligible (Kappa: 0.049, p=0.223). A minimal but statistically significant agreement was noted for blaOXA-48-like detection (Kappa: 0.314, p=0.007), while no significant agreement was observed for blaNDM-1, blaNDM-5, or blaKPC genes. The mCIM had an overall sensitivity of 3.63%, specificity of 100%, PPV of 100%, and NPV of 1.8%. It exhibited the highest sensitivity (4.3%) and specificity (100%) for blaOXA-48-like genes, with the highest PPV for blaOXA-48-like (100%), and NPV for blaKPC (98.1%). No statistically significant agreement was found between mCIM and PCR for carbapenemase detection (Kappa: 0.001, p=0.850).

Conclusions: Comprehensive assessment of the diagnostic accuracy of MHT and mCIM using WGS across a broad spectrum of multi-drug-resistant (MDR) organisms should be conducted at multiple centers to produce reliable data that can guide better clinical management of the patients.