# Evaluation of Three Phenotypic Methods for Detecting Metallo-β-Lactamase in Clinical Isolates of Acinetobacter baumannii

## TL;DR

This study compares three methods for detecting metallo-β-lactamase in Acinetobacter baumannii, finding the E-test to be the most accurate for identifying drug-resistant strains.

## Contribution

The study evaluates and compares the effectiveness of three phenotypic methods for MBL detection in A. baumannii clinical isolates.

## Key findings

- The MBL E-test detected MBL production in 100% of carbapenem-resistant A. baumannii isolates.
- The Modified Hodge Test detected MBL in 95.45% of isolates, while the Double-Disk Synergy Test detected it in 90.9%.
- The MBL E-test showed superior accuracy compared to the other two phenotypic methods.

## Abstract

Background

Carbapenem resistance mediated by metallo-β-lactamase (MBL) production in Acinetobacter baumannii represents a growing global health threat. Early detection of MBL-producing organisms is essential for the prompt administration of appropriate therapy to effectively manage infections.

Materials and methods

This cross-sectional study was conducted in the Department of Microbiology, Index Medical College Hospital and Research Centre (IMCHRC), Indore, from October 2019 to September 2021. A. baumannii strains showing resistance or intermediate susceptibility to imipenem and meropenem were subjected to MBL detection using phenotypic methods, namely the Modified Hodge Test (MHT), Double-Disk Synergy Test (DDST), and MBL E-test.

Results

Out of 143 clinical isolates of A. baumannii, 132 isolates were resistant to carbapenems across various clinical specimens. Among these 132 carbapenem-resistant A. baumannii (CRAB) isolates, MBL production was detected in 132 (100%) by the E-test, 126 (95.45%) by MHT, and 120 (90.9%) by DDST. Six isolates (4.54%) were negative by MHT, and 12 isolates (9.1%) were negative by DDST. Sensitivity and specificity of the phenotypic methods were analyzed using the MBL E-test as the gold standard for detecting MBL production in CRAB isolates.

Conclusions

Clinical isolates of A. baumannii producing MBL should be routinely screened in diagnostic laboratories to help control resistance and guide therapy, as MBL production is associated with multidrug resistance and confers resistance to carbapenems, which are reserved for severe infections. Among the phenotypic methods, the MBL E-test demonstrated superior accuracy compared to MHT and DDST for detecting MBL-producing A. baumannii isolates.