Evaluation of high-concentration EDTA-modified carbapenemase inactivation method (eCIM) for SPM-producing Pseudomonas aeruginosa.

ABSTRACT

The modified carbapenemase inactivation method (mCIM) and EDTA-modified carbapenemase inactivation method (eCIM) are simple and cost-effective detection methods used for serine- and metallo-carbapenemase determination; however, poor test performance has been reported for IMP- and SPM-producing P. aeruginosa. Recently, we reported that 40 µM EDTA concentrations improved test sensitivity for IMP-producing P. aeruginosa. Herein, we assessed standard and high-concentration EDTA eCIM against SPM-producing P. aeruginosa. Twenty-four SPM-producing P. aeruginosa were evaluated, and 3 well-characterized P. aeruginosa (wild type, n = 1; KPC, n = 1; and VIM, n = 1) were used for quality control. mCIM was conducted as described by the Clinical and Laboratory Standards Institute. Concurrently, eCIM methods were performed at standard (5 µM) and high (40 µM) EDTA concentrations. All mCIM phenotypes responded concordant with its genotype. eCIM phenotype matched its genotype for 3 and 24 SPM-producing isolates using standard and high EDTA concentrations, respectively. The eCIM sensitivity increased from 12% using standard concentrations to 100% using high EDTA concentrations. No EDTA-related adverse effects were observed on bacteria growth. The combination mCIM with 40 µM EDTA eCIM properly captured SPM-producing P. aeruginosa. This methodology should be validated in a multi-center study with various enzymatic-producing P. aeruginosa.