Comparison of Multiple Carbapenemase Tests Based on an Unbiased Colony-Selection Method

Area of Science:

• Clinical Microbiology
• Infectious Diseases
• Molecular Diagnostics

Background:

• Carbapenemase-producing organisms (CPOs) pose a significant public health threat.
• Accurate and sensitive diagnostic methods are crucial for CPO detection.
• Current CPO tests show discrepancies, partly due to biased bacterial colony selection.

Purpose of the Study:

• To evaluate the impact of unbiased colony selection on carbapenemase testing accuracy.
• To compare the FirstAll method with conventional colony selection for CPO detection.
• To assess the performance of various CPO diagnostic tests with unbiased colony selection.

Main Methods:

• Employed the FirstAll method for unbiased colony selection.
• Compared FirstAll with conventional colony selection for multiplex PCR (MPCR).
• Evaluated modified carbapenem inactivation method/EDTA-modified carbapenem inactivation method (mCIM/eCIM), Carba5, CPO panel, and MPCR performance.

Main Results:

• The FirstAll method significantly improved carbapenemase detection rates, reducing false negatives by approximately 11.2%.
• Carba5 and CPO panel showed suboptimal performance (sensitivity/specificity: 74.6%/89.5% and 77.2%/74.4%, respectively) compared to FirstAll.
• Carba5 and CPO panel results correlated well with ceftazidime-avibactam MICs, especially for carbapenemase classes A and D.

Conclusions:

• The FirstAll unbiased colony selection method demonstrably impacts carbapenemase testing.
• Using FirstAll revealed lower diagnostic performance for Carba5 and CPO panel tests.
• Ceftazidime-avibactam guidance based on Carba5 or CPO panel results remains appropriate.