Evaluation of the EDTA-Modified Carbapenem Inactivation Method for Detecting Metallo-β-Lactamase-Producing...

Area of Science:

• Clinical Microbiology
• Antimicrobial Resistance
• Molecular Diagnostics

Background:

• Increasing prevalence of carbapenem-resistant Pseudomonas aeruginosa poses significant therapeutic and infection control challenges.
• Accurate identification of carbapenemase-producing P. aeruginosa is crucial for guiding treatment and preventing outbreaks.
• Existing phenotypic methods require optimization for reliable detection and differentiation of carbapenemase types.

Purpose of the Study:

• To evaluate the performance of the modified carbapenem inactivation method (mCIM) and EDTA-modified CIM (eCIM) for detecting carbapenemase production in P. aeruginosa.
• To assess the ability of these phenotypic tests to distinguish between metallo-β-lactamase and serine-carbapenemase production.
• To identify necessary modifications for improving the sensitivity of the mCIM for specific carbapenemase-producing isolates.

Main Methods:

• Clinical P. aeruginosa isolates (n=103) were tested using the standard mCIM and eCIM protocols.
• The mCIM was performed according to Clinical and Laboratory Standards Institute guidelines.
• Modifications to the mCIM, including double inoculum and prolonged incubation, were evaluated for enhanced sensitivity. Genotypic profiles served as the reference standard.

Main Results:

• The mCIM correctly identified carbapenemase producers in 91% of isolates; Guiana extended-spectrum (GES)-type producers were primarily discordant.
• Modified mCIM protocols achieved 100% sensitivity for GES-harboring isolates.
• The eCIM showed 100% concordance for Verona integron-encoded metallo-β-lactamases (VIM) and New Delhi metallo-β-lactamases (NDM) but failed to detect imipenemase (IMP) and Sao Paulo metallo-β-lactamases (SPM). KPC and GES isolates tested negative with eCIM as expected.

Conclusions:

• Conventional mCIM and eCIM effectively identify KPC, VIM, and NDM-producing P. aeruginosa.
• Modifications to the mCIM are required to improve the detection of GES, IMP, and SPM carbapenemase types.
• Combined phenotypic testing with appropriate modifications offers a valuable tool for clinical laboratories to guide antimicrobial therapy and infection control strategies.