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

Abstract

Two carbapenem-non-susceptibleKlebsiella pneumoniaeisolates, Z2554 and Z2110, were collected from a hospital in China and analysed by PFGE.K. pneumoniaeZ2554 and Z2110 were genetically unrelated and showed resistance to ertapenem, and reduced susceptibility to imipenem and meropenem. Analysis of theirβ-lactamases indicated thatK. pneumoniaeZ2554 produced TEM-1 and CTX-M-14β-lactamases, whilst Z2110 produced a plasmid-mediated AmpCβ-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 theompK35sequence ofK. pneumoniaeZ2554 and Z2110 contained a number of silent mutations. InompK36, 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 fromK. pneumoniae subsp.pneumoniaeMGH 78578. It was concluded thatβ-lactamase production combined with OmpK36 deficiency results in ertapenem resistance, and reduced imipenem and meropenem susceptibility, inK. pneumoniaeZ2554 and Z2110. OmpK36 may play an important role in the resistance or reduced susceptibility to carbapenems inK. pneumoniaeproducing AmpC, extended-spectrumβ-lactamase or broad-spectrumβ-lactamase.