Emergence of Serratia marcescens , Klebsiella pneumoniae , and Escherichia coli Isolates Possessing the Plasmid-Mediated Carbapenem-Hydrolyzing β-Lactamase KPC-2 in Intensive Care Units of a Chinese Hospital

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Abstract
Twenty-one Serratia marcescens , ten Klebsiella pneumoniae , and one Escherichia coli isolate with carbapenem resistance or reduced carbapenem susceptibility were recovered from intensive care units (ICUs) in our hospital. Enterobacterial repetitive intergenic consensus-PCR and pulsed-field gel electrophoresis demonstrated that all the S. marcescens isolates belonged to a clonal strain and the 10 K. pneumoniae isolates were indistinguishable or closely related to each other. The MICs of imipenem, meropenem, and ertapenem for all isolates were 2 to 8 μg/ml, except for K. pneumoniae K10 (MICs of 128, 256, and >256 μg/ml). Isoelectric focusing, PCRs, and DNA sequencing indicated that all S. marcescens isolates produced KPC-2 and a β-lactamase with a pI of 6.5. All K. pneumoniae isolates produced TEM-1, KPC-2, CTX-M-14, and a β-lactamase with a pI of 7.3. The E. coli E1 isolate produced KPC-2, CTX-M-15, and a β-lactamase with a pI of 7.3. Conjugation studies with E. coli (EC600) resulted in the transfer of reduced carbapenem susceptibility compared to that of the original isolates, and only the bla KPC-2 gene was detected in E. coli transconjugants. Plasmid restriction analysis showed identical restriction patterns among all E. coli transconjugants. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis and ompK35/36 gene sequence analysis of outer membrane proteins revealed that K. pneumoniae K10 failed to express OmpK36, because of insertional inactivation by an insertion sequence IS Ecp1 . All these results indicate that KPC-2-producing S. marcescens , K. pneumoniae , and E. coli isolates emerged in ICUs in our hospital. KPC-2 combined with porin deficiency results in high-level carbapenem resistance in K. pneumoniae . The same bla KPC-2 -encoding plasmid was spread among the three different genera.

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