Phenotypic and Molecular Strategies for Identifying Extended-Spectrum β-Lactamases: A Comprehensive Narrative Review

Abstract

Extended-Spectrum β-Lactamases (ESBLs) are enzymes that confer resistance to third-generation cephalosporins, penicillins, and aztreonam, posing a serious global threat to antimicrobial therapy and infection control. Accurate and timely detection of ESBL-producing organisms is essential for appropriate clinical management, epidemiological surveillance, and implementation of infection prevention measures. This narrative review comprehensively explores both phenotypic and molecular strategies employed for the identification of ESBLs in clinical microbiology laboratories. Phenotypic methods remain the cornerstone for initial screening and confirmation of ESBL production due to their cost-effectiveness and applicability in routine diagnostic setups. Screening tests, such as the disk diffusion method and automated susceptibility testing systems, are commonly used to identify potential ESBL producers. Confirmatory tests—such as the combined disk test, double-disk synergy test (DDST), and E-test—rely on the inhibition of β-lactamase activity by clavulanic acid and remain widely accepted for their simplicity and reliability. However, these methods may face limitations in detecting co-existing resistance mechanisms, such as AmpC β-lactamases or carbapenemases, which can mask ESBL activity. Molecular techniques have emerged as powerful tools for the precise detection and characterization of ESBL genes. Polymerase chain reaction (PCR) and multiplex PCR allow rapid identification of common ESBL gene families, including bla_TEM, bla_SHV, and bla_CTX-M. Advanced sequencing technologies, such as real-time PCR, DNA microarray, and whole-genome sequencing (WGS), enable in-depth analysis of gene variants, mobile genetic elements, and clonal dissemination patterns. Although molecular approaches offer superior specificity and sensitivity, their use is often constrained by high cost, technical expertise requirements, and limited availability in low-resource settings. This review emphasizes the complementary roles of phenotypic and molecular methods in ESBL detection. A combined diagnostic approach can enhance accuracy, guide appropriate antimicrobial therapy, and strengthen surveillance programs aimed at combating multidrug resistance. Future research should focus on developing rapid, affordable, and point-of-care diagnostic tools integrating both phenotypic and genotypic insights to support effective antimicrobial stewardship and global public health interventions.

Journal of Current and Advance Medical Research, July 2024;11(2):115-122