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J Med Microbiol 58 (2009), 1196-1202; DOI: 10.1099/jmm.0.008094-0
© 2009 Society for General Microbiology
ISSN 0022-2615

Reduced susceptibility to carbapenems in Klebsiella pneumoniae clinical isolates associated with plasmid-mediated β-lactamase production and OmpK36 porin deficiency

Xuan Ding Wang, Jia Chang Cai, Hong Wei Zhou, Rong Zhang and Gong-Xiang Chen

2nd Affiliated Hospital of Zhejiang University, Zhejiang University, 88 Jiefang Road, Hangzhou 310009, PR China

Correspondence
Gong-Xiang Chen
chengong218{at}163.com

Received November 17, 2008
Accepted May 12, 2009

Two carbapenem-non-susceptible Klebsiella pneumoniae isolates, Z2554 and Z2110, were collected from a hospital in China and analysed by PFGE. K. pneumoniae Z2554 and Z2110 were genetically unrelated and showed resistance to ertapenem, and reduced susceptibility to imipenem and meropenem. Analysis of their β-lactamases indicated that K. pneumoniae Z2554 produced TEM-1 and CTX-M-14 β-lactamases, whilst Z2110 produced a plasmid-mediated AmpC β-lactamase, DHA-1, in addition to TEM-1 and CTX-M-14. SDS-PAGE analysis of the outer-membrane proteins (OMPs) revealed that both isolates lacked an OMP of ~39 kDa (OmpK36), whilst Z2110 had an additional protein with an approximate molecular mass of 26 kDa. Analysis of the OMP-encoding genes demonstrated that the ompK35 sequence of K. pneumoniae Z2554 and Z2110 contained a number of silent mutations. In ompK36, several insertions and deletions of short DNA fragments (1–6 bp) were detected in both isolates. The N-terminal sequence of the ~26 kDa protein band identified in Z2110 had no similarity to the sequence of OmpK36. Instead, it shared high similarity with hypothetical protein KPN_03267 originating from K. pneumoniae subsp. pneumoniae MGH 78578. It was concluded that β-lactamase production combined with OmpK36 deficiency results in ertapenem resistance, and reduced imipenem and meropenem susceptibility, in K. pneumoniae Z2554 and Z2110. OmpK36 may play an important role in the resistance or reduced susceptibility to carbapenems in K. pneumoniae producing AmpC, extended-spectrum β-lactamase or broad-spectrum β-lactamase.






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