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

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 10 μ,L loop) in 400 μ,L water, in which a 10 μ,g disk of meropenem/imipenem is immersed. After 2 h 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): ≤ 19 mm, positive; ≥ 25 mm negative; 20-24 mm, 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