EDTA-modified carbapenem inactivation method (eCIM) for detecting IMP Metallo-β-lactamase–producing Pseudomonas aeruginosa: an assessment of increasing EDTA concentrations

Abstract

Background: Prompt identification of carbapenemase-harboring organisms is valuable in informing therapeutic and infection-control measures. The modified carbapenem inactivation method (mCIM) and EDTA-modified carbapenem inactivation method (eCIM) are inexpensive and easy to interpret phenotypic tests endorsed by the Clinical and Laboratory Standards Institute (CLSI) for the detection of carbapenemase-harboring Enterobacterales. Only mCIM is endorsed by CLSI for detecting carbapenemase-harboring Pseudomonas aeruginosa. eCIM's ability to delineate serine and metallo-β-lactamases (MBL) could be advantageous in areas prevalent with carbapenemaseharboring P. aeruginosa. A recent assessment of mCIM/eCIM on MBL-harboring P. aeruginosa demonstrated high eCIM sensitivity for NDMs and VIMs but not for IMP-producers. Therefore, this study aimed to determine whether increasing EDTA concentrations would enhance eCIM sensitivity for a collection of IMP-harboring P. aeruginosa isolates. Twenty-six IMP-harboring P. aeruginosa isolates were utilized. For test validation, additional P. aeruginosa isolates harboring NDM (n = 3), VIM (n = 3), KPC (n = 8), wild-type (n = 1), and Enterobacterales isolates harboring IMP (n = 6) and NDM (n = 1) were assessed. The mCIM test was conducted as outlined by CLSI. Simultaneously, the eCIM test was performed with the standard 5 mM EDTA concentration and doubling EDTA concentrations: 10 mM, 20 mM, and 40 mM. Results: Concentration-dependent improvement was observed among the IMP-harboring P. aeruginosa with eCIM sensitivities at 0, 31, 85, and 100% respectively. Remaining Enterobacterales and P. aeruginosa responded concordantly with their genotype at the standard 5 mM eCIM concentration, with doubling EDTA concentrations providing no greater sensitivity. Conclusion: Combination of mCIM and an eCIM with a 40 mM EDTA concentration appropriately capture IMPharboring P. aeruginosa without sacrificing test utility for other carbapenemase-harboring isolates.

Carbapenemase-producing Pseudomonas aeruginosa –an emerging challenge

“…Several commercial tests have been shown to be accurate for detection of carbapenemases or carbapenem resistance genes, although the costs of the tests may vary from country to country. It should be noted that the mCIM test can have difficulty detecting some carbapenemases, such as IMP [ 27 , 28 ], although a recent study showed the combination of mCIM and eCIM testing to be effective for detecting most other carbapenemases in P. aeruginosa isolates [ 29 ].

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Metallo-β-lactamases and a tug-of-war for the available zinc at the host–pathogen interface

“…Addition of DPA to cells expressing a set of clinically relevant MBLs showed inhibitory profiles depending on the enzyme [8]. Cells producing SPM-1 or IMP-1 were much less affected than those expressing NDM-1 or VIM-2, both in E. coli and in Pseudomonas aeruginosa [24,25]. Zn(II) dissociation in the periplasm inactivated MBLs and led to a time-dependent decrease of the protein levels in this compartment, revealing that metal binding is essential for in vivo stability of these enzymes, that is, apo-MBLs (devoid of metal ions) are unstable in the periplasm [8].…”

Assessment of Colistin Susceptibility among Carbapenem-Resistant Clinical Isolates

“…These pathogens are included in both types of human infections, hospital and community with frequently express resistance to most antibiotics classes 2 . Thus, the determination of carbapenemase-producing organisms is paramount for treatment decisions beside infection control 3 .…”