A comparison of phenotypic methods for the detection of carbapenemase in Klebsiella pneumoniae

Abstract

Introduction: Carbapenem-resistant Klebsiella pneumoniae (CRKP) isolates are increasingly spreading in the community and pose a serious public health threat. Rapid and accurate detection of these isolates is therefore critical. This study aimed to evaluate the performance of combined disc method, the carbapenem inactivation method (mCIM) and its modifications.

Methodology: A total of 100 K. pneumoniae isolates collected from various clinical samples between 2018 and 2021 were included. Carbapenemase production was investigated using the combined disc method, mCIM (19 mm and 22mm), and aCIM (19 mm and 22 mm). Carbapenemase types were determined using the combined disc method, eCIM, and mCIMplus. Resistance genes were detected by real-time PCR, which was used as the reference method to evaluate the performance of phenotypic tests.

Results: For carbapenemase detection, the sensitivities of combined disc method, mCIM-19 mm, mCIM-22 mm, aCIM-19 mm, and aCIM-22 mm were 100%, 84.8%, 95.7%, 83.7% and 95.7%, respectively, while the specificities are 62.5%, 100%, 25%, 100%, and 62.5%. For carbapenemase species detection, the sensitivities of the combined disc method, eCIM-19 mm, eCIM-22 mm, and mCIMplus were 98,9%, 75.4%, 84% and 26.1%, respectively; the specificities were 62.5%, 48.8%, 42% and 100%. No significant differences were observed between the mCIM and aCIM tests. (p value:1 for 19 mm, p value:0.37 for 22 mm).

Conclusions: The combined disc method provided the most effective balance of performance and practicality. However, phenotypic methods may be insufficient for isolates harboring multiple resistance genes.