ABSTRACT
We
investigated a Klebsiella oxytoca isolate demonstrating
resistance to imipenem, meropenem, extended-spectrum cephalosporins,
and aztreonam. The MICs of both imipenem and meropenem were 32μ
g/ml. The β-lactamase activity against imipenem and
meropenem was inhibited in the presence of clavulanic acid. Isoelectric
focusing studies demonstrated five β-lactamases with pIs of 8.2
(SHV-46), 6.7 (KPC-2), 6.5 (unknown), 6.4 (probable OXY-2), and 5.4
(TEM-1). The presence of the bla
SHV and
bla
TEM genes was confirmed by specific PCR assays
and DNA sequence analysis. Transformation and conjugation studies with
Escherichia coli showed that the β-lactamase with a pI
of 6.7, Klebsiella pneumoniae carbapenemase-2 (KPC-2), was
encoded on an approximately 70-kb conjugative plasmid that also carried
SHV-46, TEM-1, and the β-lactamase with a pI of 6.5. The
bla
KPC-2 determinant was cloned in E. coli
and conferred resistance to imipenem, meropenem, extended-spectrum
cephalosporins, and aztreonam. The amino acid sequence of KPC-2 showed
a single amino acid difference, S174G, when compared with KPC-1,
another carbapenem-hydrolyzing β-lactamase from K.
pneumoniae 1534. Hydrolysis studies showed that purified KPC-2
hydrolyzed not only carbapenems but also penicillins, cephalosporins,
and aztreonam. KPC-2 had the highest affinity for meropenem. The
kinetic studies revealed that KPC-2 was inhibited by clavulanic acid
and tazobactam. An examination of the outer membrane proteins of the
parent K. oxytoca strain demonstrated that it expressed
detectable levels of OmpK36 (the homolog of OmpC) and a
higher-molecular-weight OmpK35 (the homolog of OmpF). Thus, carbapenem
resistance in K. oxytoca 3127 is due to production of the Bush
group 2f, class A, carbapenem-hydrolyzing β-lactamase KPC-2.
This β-lactamase is likely located on a transposon that is part
of a conjugative plasmid and thus has a very high potential for
dissemination.
Carbapenem-Resistant Strain of Klebsiella
oxytoca Harboring Carbapenem-Hydrolyzingβ
-Lactamase
KPC-2
