Evaluation Of The Antimicrobial Efficacy Of Copper Solution Against Carbapenemase-Producing Gram-Negative Clinical Isolates

Abstract

Urinary tract infections (UTIs) caused by multidrug-resistant uropathogenic Escherichia coli (MDR UPEC) present an increasing clinical challenge, particularly with the emergence of metallo-β-lactamases (MBLs) that confer resistance to carbapenems, the last-resort antibiotics used to manage severe Gram-negative infections. The declining effectiveness of conventional antimicrobial agents necessitates the urgent exploration of alternative therapeutic strategies. This study evaluated the in vitro antimicrobial activity of copper sulfate (CuSO₄) against carbapenem-resistant MDR UPEC isolates and characterized their resistance profiles at both phenotypic and molecular levels. A total of 70 urine samples were collected from patients with clinical features of UTIs, and 50 UPEC isolates were identified using standard biochemical methods. Antimicrobial susceptibility testing was performed using the Kirby-Bauer disk diffusion method against a panel of 24 antibiotics, confirming multidrug resistance in all isolates. Phenotypic detection of carbapenem resistance was conducted using the Modified Hodge Test (MHT), the Modified Carbapenem Inactivation Method (mCIM), and the EDTA-modified Carbapenem Inactivation Method (eCIM). The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of CuSO₄ were determined to quantify its antimicrobial efficacy. Additionally, genomic and plasmid DNA extraction was performed to support the molecular characterization of resistance determinants. The minimum inhibitory concentration (MIC) of CuSO₄ was 1600 µg/mL for 90% of the isolates, indicating consistent inhibitory activity across the group. Genomic DNA was successfully extracted from 40 out of 50 isolates, while plasmid DNA was recovered from 30 out of 50 isolates. This success enabled downstream molecular analysis of resistance gene carriage. These findings demonstrate that CuSO₄ exhibits reliable in vitro antimicrobial activity against carbapenem-resistant, multidrug-resistant UPEC, supporting its potential as an alternative or adjunctive antimicrobial agent amid rising carbapenem resistance.