Reduced Incubation Time of the Modified Carbapenem Inactivation Test and Performance of Carbapenem Inactivation in a Set of Carbapenemase-Producing Enterobacteriaceae with a High Proportion of bla IMP Isolates.

Accurate and timely identification of carbapenemase-producing Enterobacteriaceae (CPE) is critical for microbiology laboratories in order to facilitate infection prevention, reduce the spread of multiresistant Gram-negative bacilli, and reduce delays to effective antibiotic therapy. We undertook a study to compare the carbapenem inactivation method (CIM) against the modified carbapenem inactivation method (mCIM) on a broad range of CPE isolates from Australia, including a high proportion of bla IMP isolates. Furthermore, we evaluated the performance of the mCIM with a reduced incubation time using automated incubation and digital plate reading in order to better facilitate quick confirmation of carbapenemases. The overall sensitivity of the mCIM was 98.2%, compared to 95.6% for the CIM. The minimum incubation time for the mCIM while maintaining its sensitivity was 12 hours. Both the CIM and mCIM perform well on a broad range of CPE isolates seen in Australia.