Detection of carbapenemase-producing Pseudomonas aeruginosa: Evaluation of the carbapenem inactivation method (CIM)

Abstract

Introduction: The carbapenem inactivation method (CIM) is a cost-effective assay for detecting carbapenemases. However, its interpretation is unclear for Pseudomonas spp. We evaluate its accuracy when meropenem is changed to imipenem.

Methods: We analyzed 266 P. aeruginosa isolates. The CIM method consists of: resuspend bacterial colonies (a full 10μL loop) in 400μL water, in which a 10μg disk of meropenem/imipenem is immersed. After 2h of incubation (35°C), remove the disk, place it onto a Mueller-Hinton agar plate previously inoculated with Escherichia coli (ATCC 25922), and incubate at 35 ̊C between 18-24 h. Interpretation criteria (mm of inhibition zone): ≤19mm, positive; ≥25mm negative; 20-24mm, undetermined.

Results: Imipenem improves the sensitivity and specificity of CIM when compared to meropenem (99.4% and 98.9%, vs. 91.9% and 94.7%, respectively).

Conclusions: The accuracy of CIM for carbapenemase detection in P. aeruginosa is increased with the use of imipenem.

Keywords: Carbapenem inactivation method; Carbapenemasas; Carbapenemases; Carbapenemases phenotypic detection; Detección fenotípica; Método de inactivación del carbapenémico; Pruebas de tamizaje; Pseudomonas aeruginosa; Screening test.