Comparison of Four Carbapenemase Detection Methods for bla(KPC-2) Variants

Recently, various bla(KPC-2) variants resistant to ceftazidime-avibactam have begun to emerge in clinical settings, but it is unclear which testing method is most appropriate for detecting these variants. Strains were subjected to antimicrobial susceptibility testing using the broth microdilution method. Four carbapenemase detection methods, modified carbapenem inactivation method (mCIM) and EDTA carbapenem inactivation method (eCIM), APB/EDTA (carbapenemase inhibitor APB [3-aminophenylboronic acid] and EDTA enhancement method), NG-test Carba 5, and GeneXpert Carba-R were used to try to detect KPC-2 variants in 19 Klebsiella pneumoniae isolates. Among those bla(KPC-2) variants, bla(KPC-33)-, bla(KPC-35)-, bla(KPC-71)-, bla(KPC-76)-, bla(KPC-78)-, and bla(KPC-79)-positive isolates accounted for 26.3% (5/19), 15.8% (3/19), 5.3% (1/19), % 42.1% (8/19), 5.3% (1/19), and 5.3% (1/19), respectively. All 19 K. pneumoniae carrying bla(KPC-2) variants showed resistance to ceftazidime-avibactam (MICs:16 to >64 mg/L), and 14 strains were susceptible to imipenem (MICs: 0.25 to 1 mg/L). None of the bla(KPC-2) variants could be detected using either the mCIM or the APB/EDTA method, while five strains carrying bla(KPC-2) variants (bla(KPC-35), bla(KPC-78), and bla(KPC-79)) tested KPC positive when using NG-test Carba 5. However, GeneXpert Carba-R was able to detect bla(KPC-2) variants (harboring bla(KPC-33), bla(KPC-35), bla(KPC-71), bla(KPC-76), bla(KPC-78), and bla(KPC-79)) carried by all 19 K. pneumoniae. The emergence of new KPC variants poses an increased challenge for carbapenemase detection methods, and laboratories should use the appropriate assays to accurately detect these variants. IMPORTANCE Carbapenemase detection is essential for the appropriate treatment of CRE infections. Several clinical laboratories have begun using relevant carbapenemase assays such as mCIM and eCIM, the APB/EDTA method, NG-test Carba 5, and GeneXpert Carba-R to detect carbapenemases. Nevertheless, some of these methods may have limitations for detecting bla(KPC-2) variants. Additionally, there has been little relevant research on evaluate the differences between these standard methods for detecting bla(KPC-2) variants. Therefore, we investigated the reliability of these classic methods for assessing 19 K. pneumoniae with bla(KPC-2) variants. Our results showed that none of the bla(KPC-2) variants could be detected using either the mCIM or APB/EDTA method, while five strains (harboring bla(KPC-35), bla(KPC-78),and bla(KPC-79)) tested KPC positive when using NG-test Carba 5. GeneXpert Carba-R could detect six bla(KPC-2) variants carried by all 19 K. pneumoniae. This study may be valuable for clinical laboratories in their efforts to test for various bla(KPC-2) variants.