Antibiotic Resistance in Metallo-β-Lactamase-Producing Pseudomonas aeruginosa in Clinical Isolates: Challenges and Phenotypic Detection in a Tertiary Care Setting

Abstract

Background: Pseudomonas aeruginosa is a major cause of hospital infections because of its drug resistance mechanisms and ecological adaptability. It can survive on both living and non-living surfaces, including antiseptic solutions, and can spread resistance in hospitals. Metallo-beta-lactamases (MBLs) are resistant to current β-lactamase inhibitors, with no new inhibitors in development, making their spread a serious clinical concern. Rapid identification of MBLs is vital for patient care and infection control. This study aims to estimate the accuracy of phenotypic tests for detecting MBL-producing Pseudomonas aeruginosa isolates.

Material and methods: This laboratory based study was carried out in the Department of Microbiology throughout the course of two years (November 2021 to November 2023). A total of 410 Pseudomonas aeruginosa isolates were obtained and of which 118 isolates that were resistant to imipenem coming from clinical samples of both outpatients and inpatients were tested for metallo-beta-lactamase (MBL) production using phenotypic methods including the Imipenem-EDTA Combined Disc Test, Ceftazidime- EDTA Combined Disc Test and Double Disc Synergy Test.

Result: In this investigation, it was found that 110 out of 118 imipenem resistant clinical isolates were positive for MBL production. The Imipenem-EDTA combined disc test identified 75.42% of the positive cases, while the Ceftazidime-EDTA combined disc test found 77.11%, and the double disc synergy test detected 50%. Most MBL-producing isolates were from urine samples (50.9%), primarily isolated from the surgical ward (29.10%). Sensitivity to cefepime was observed in 30% of the isolates, followed by amikacin (25.45%). The overall prevalence of MBL-producing Pseudomonas aeruginosa was 26.82%.

Conclusion: Acquired MBLs observed in Pseudomonas aeruginosa are a major concern attributed to their ease of spread and broad antibiotic resistance. In this study, 26.82% of strains were MBL producers, mostly from the surgery ward, with high resistance to Imipenem (100%), Ceftriaxone (98.19%), and Polymyxin B (98.19%). Some sensitivity was noted to Cefepime (30%) and Amikacin (25.45%). Imipenem –EDTA combined disc test (CDT) and Imipenem –EDTA double disc synergy test (DDST), which are affordable and simple to perform, must be implemented in each clinical microbiology laboratory to identify MBLs in Pseudomonas aeruginosa and to enhance disease management.