A Novel KPC Variant KPC-55 inKlebsiella pneumoniaeST307 of Reinforced Meropenem-Hydrolyzing Activity

A novelKlebsiella pneumoniaecarbapenemase (KPC) variant, KPC-55, produced by aK. pneumoniaeST307 strain was characterized.K. pneumoniaestrain BS407 was recovered from an active surveillance rectal swab of a patient newly admitted to a general hospital in Busan, South Korea. Carbapenemase production was confirmed by the modified Hodge test, and the MICs of beta-lactams were determined by the broth microdilution method. The whole genome was sequenced. Cloning and expression of thebla(KPC-55)gene inEscherichia coliand MIC determination were performed. The enzyme KPC-55 was used for kinetic assays against beta-lactams and compared with the KPC-2 enzyme. The new allele of thebla(KPC)gene had a T794A alteration compared to thebla(KPC-2)gene, resulting in the amino acid substitution Y264N in the middle of the beta 9-sheet. Compared to the KPC-2-producing strain, the KPC-55-producing strain exhibited a lower level of resistance to most beta-lactam drugs tested, however, the KPC-55 enzyme catalyzed aztreonam and meropenem at an increased efficiency compared to the catalytic activity of KPC-2. KPC subtypes could have varied phenotypes due to alterations in amino acid sequences, and such an unexpected resistance phenotype emphasizes the importance of detailed characterizations for the carbapenemase-producing Enterobacterales.