Novel carbapenem-hydrolyzing beta-lactamase, KPC-1, from a carbapenem-resistant strain of Klebsiella pneumoniae

A Klebsiella pneumoniae isolate showing moderate to high-level imipenem and meropenem resistance was investigated. The MICs of both drugs were 16 mug/ ml. The beta -lactamase activity against imipenem and meropenem was inhibit ed in the presence of clavulanic acid. The strain was also resistant to ext ended-spectrum cephalosporins and aztreonam, Isoelectric focusing studies d emonstrated three beta -lactamases, with pIs of 7.2 (SHV-29), 6.7 (KPC-L), and 5.4 (TEM-1). The presence of bla(SHV) and bla(TEM) genes was confirmed by specific PCRs and DNA sequence analysis. Transformation and conjugation studies with Escherichia coli showed that the beta -lactamase with a pI of 6,7, KPC-1 (X, pneumoniae carbapenemase-l), was encoded on an approximately 50-kb nonconjugative plasmid, The gene, bla(KPC-1), was cloned in E. coli and shown to confer resistance to imipenem, meropenem, extended-spectrum ce phalosporins, and aztreonam, The amino acid sequence of the novel carbapene m-hydrolyzing beta -lactamase, KPC -1, showed 45% identity to the pI 9.7 ca rbapenem-hydrolyzing beta -lactamase, Sme-l, from Serratia marcescens S6, H ydrolysis studies showed that purified KPC-1 hydrolyzed not only carbapenem s but also penicillins, cephalosporins, and monobactams. KPC-1 had the high est affinity for meropenem, The kinetic studies also revealed that clavulan ic acid and tazobactam inhibited KPC-1, An examination of the outer membran e proteins of the parent K, pneumoniae strain demonstrated that the strain does not express detectable levels of OmpK35 and OmpK37, although OmpK36 is present. We concluded that carbapenem resistance in K, pneumoniae strain 1 534 is mainly due to production of a novel Bush group 2f, class A, carbapen em- hydrolyzing beta -lactamase, KPC -1, although alterations in porin expr ession may also play a role.