Review of phenotypic assays for detection of extended-spectrum β-lactamases and carbapenemases: a microbiology laboratory bench guide

Dickson Aruhomukama

doi:10.4314/ahs.v20i3.11

Abstract

Infections caused by gram-negative antibiotic-resistant bacteria continue to increase. Despite recommendations by the Clinical Laboratory Standards Institute (CLSI) and the European Committee on Antimicrobial Susceptibility Testing (EUCAST) with regards to detection of antibiotic degrading enzymes secreted by these bacteria, the true prevalence of extended-spectrum β-lactamase (ESBL) and carbapenemase producers remains a difficult task to resolve. Describing of previously designed phenotypic detection assays for ESBLs and carbapenemases in a single document avails a summary that allows for multiple testing which increases the sensitivity and specificity of detection. This review, therefore, defined and classified ESBLs and carbapenemases, and also briefly described how the several previously designed phenotypic detection assays for the same should be performed. Extended-spectrum β-lactamase and carbapenemase detection assays, once performed correctly, can precisely discriminate between bacteria producing these enzymes and those with other mechanisms of resistance to β-lactam antibiotics.

Highlights

Infections involving extended-spectrum β-lactamase and carbapenemase producing gram-negative bacteria continue to increase in health-care settings[1,2]
Increased β-lactam resistance in bacteria is due to their continuous exposure to β-lactam antibiotics, this has contributed to increased uninterrupted production and mutation of β-lactamases in Corresponding author: Dickson Aruhomukama, Department of Medical Microbiology, College of Health Sciences, Makerere University, Kampala, Uganda
The true prevalence of ESBL and carbapenemase producing bacteria remains a difficult task to resolve despite the recommendations provided by Clinical Laboratory Standards Institute (CLSI) and European Committee on Antimicrobial Susceptibility Testing (EUCAST) for detection of these enzymes[1,5,6,7,8]

Summary

Introduction

Infections involving extended-spectrum β-lactamase and carbapenemase producing gram-negative bacteria continue to increase in health-care settings[1,2]. In the DDS, testing is performed by inoculating Mueller-Hinton agar with a lawn culture of organisms for the standard diffusion method and placing onto the agar plate a commercially available disc of CTX (30μg) and/or ceftriaxone (30μg) and/or CAZ (30μg) and/or aztreonam (30μg) and a disc of amoxicillin-clavulanic acid (20/10μg) at a distance of 30mm center to center as shown in figure 1 .

Results

Conclusion