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 blaIMP isolates.

Accurate and timely identification of carbapenemase producing Enterobacteriaceae (CPEs) is critical for microbiology laboratories in order to facilitate infection prevention, reduce the spread of multi-resistant 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 whilst maintaining its sensitivity was 12 hours. Both the CIM and mCIM perform well on a broad range of CPE isolates seen in Australia.