Prevalence and mechanisms of decreased susceptibility to carbapenems in Klebsiella pneumoniae isolates

In this study, we examined the prevalence of and mechanisms of decreased susceptibility to either imipenem or meropenem in Klebsiella pneumoniae isolates. A total of 230 clinical isolates of K. pneumoniae were collected from 13 clinical laboratories from a nationwide distribution. The MICs of imipenem and meropenem were determined by the agar dilution method. To characterize the isolates with decreased susceptibility to carbapenems (MICs of >2 μg/mL), we performed polymerase chain reaction amplification of a variety of β-lactamase genes, isoelectric focusing, and outer membrane profile analysis using sodium dodecyl sulfate-polyacrylamide gel electrophoresis and mass spectrometry. Three isolates (BD6, BD8, and KN16) exhibited decreased susceptibility to carbapenems with imipenem MICs of 1, 4, and 8 μg/mL and meropenem MICs of 4, 8, and 4, respectively. Isolate BD6 produced blaTEM-1, blaSHV-12, and blaOXA-17; isolate BD8 produced blaGES-3, blaSHV-12, and blaOXA-17; and isolate KN16 produced blaTEM-11, blaSHV-12, and blaDHA-1. In all the 3 isolates, OmpK35 porin was not expressed, and in 1 isolate (KN16), OmpK36 was not expressed either. The prevalence of decreased susceptibility to carbapenems was low (1.3%), and none of them showed overt resistance to carbapenems. Decreased susceptibility to carbapenems can occur in K. pneumoniae when blaGES-3, blaTEM-11, blaSHV-12, blaOXA-17, and/or blaDHA-1 are produced in combination with porin loss. In addition, to our knowledge, this is the 1st report of blaOXA-17 in Enterobacteriaceae.