Detection of ESBL and MBL in Gram-Negative Bacilli: Phenotypic and Genotypic Approaches

Abstract

Background: Extended-Spectrum Beta-Lactamases (ESBLs) and Metallo-Beta-Lactamases (MBLs) are critical resistance mechanisms in Gram-negative bacteria, which significantly limit the therapeutic options for infections. The detection of these enzymes in clinical isolates is essential for appropriate antibiotic treatment.

Aim: To investigate the prevalence of ESBL and MBL-producing Gram-negative bacilli from clinical isolates and evaluate both phenotypic and genotypic detection methods.

Methods: A total of 200 Gram-negative bacilli isolates were collected from hospitalized patients over a period of 6 months. The isolates were tested for antimicrobial susceptibility using the disc diffusion method. Phenotypic detection of ESBL and MBL was performed using standard methods such as the double disc synergy test and the EDTA-based disk potentiation test, respectively. For genotypic identification, PCR was used to detect genes encoding ESBL (blaCTX-M, blaTEM, blaSHV) and MBL (blaIMP, blaVIM, blaSPM) enzymes.

Results: Among the 200 isolates, 40% were found to be ESBL producers and 20% were MBL producers. The phenotypic methods showed a high sensitivity for ESBL detection but moderate sensitivity for MBL detection. Genotypic analysis confirmed the presence of blaCTX-M in 80% of ESBL producers and blaVIM in 70% of MBL producers.

Conclusion: The study highlights the prevalence of ESBL and MBL-producing Gram-negative bacilli in a hospital setting. While phenotypic methods are useful, genotypic methods provide a more precise and reliable detection of resistance genes. Regular surveillance and appropriate antibiotic stewardship are essential in managing resistant infections.

Keywords: ESBL, MBL, Gram-negative bacilli, phenotypic detection, genotypic detection, antimicrobial resistance, PCR.