ABSTRACT
Objective:To assess the performance of mCIM in combination with eCIM test as well as Carba-5 and Carba-R tests in detecting common carbapenemases in carbapenem-resistant organisms (CRO).Methods:In this study, 122 non-duplicate clinical CRO strains isolated in Sir Run Run Shaw Hospital, Zhejiang University School of Medicine, from January 2019 to December 2020 were randomly selected. These strains were identified using matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS). A modified carbapenem inactivation test (mCIM combined with eCIM test), Carba-5 and Carba-R were used to detect the types of carbapenemases in these strains. PCR results were used as the gold standard to evaluate the performance of the three methods.Results:The 122 CRO strains belonged to 12 different species. PCR results showed that carbapenemases were produced in 112 strains. KPC-2-producing strains accounted for 57% (70/122), which included 46 Klebsiella pneumoniae strains, 12 Pseudomonas aeruginosa strains and 12 other strains. OXA-232-positive strains accounted for 15% (19/122), with Klebsiella pneumoniae being the only carrier (100%, 19/19). NDM carbapenemases were identified in 16% of the strains (20/122), with NDM-1 and NDM-5 accounting for 35% (7/20) and 65% (13/20), respectively, and Escherichia coli was the predominant carrier (60%, 12/20). IMP-4 was detected in one Klebsiella pneumoniae strain and one Enterobacter asteri strain. One Klebsiella pneumoniae strain produced KPC-2 and IMP-4, while none of the strains were found to produce VIM carbapenemases. In the remaining 10 strains, none of the above-mentioned carbapenemases were detected. Compared with the golden standard, the mCIM combined with eCIM test had a sensitivity of 95.65% (22/23), a specificity of 100% (90/90), a positive predictive value (PPV) of 100% (22/22), a negative predictive value (NPV) of 98.90% (90/91), and a diagnostic accuracy of 99.11% (112/113). The sensitivity, specificity, PPV, NPV and diagnostic accuracy of Carba-5 and Carba-R tests were all 100%. Conclusions:In general clinical microbiology laboratories, Carba-5 test could be used as an accurate method to quickly detect common carbapenemases in carbapenem-resistant Enterobacterales and Pseudomonas aeruginosa strains. In advanced laboratories, Carba-R test could also be used to monitor the colonization of carbapenem-resistant bacteria in patients. If the results of both Carba-5 and Carba-R tests were negative, mCIM combined with eCIM test was recommended.