Resistance to (β-lactams, and reduced susceptibility to carbapenems, in clinical isolates of Klebsiella pneumoniae due to interplay between CTX-M-15 and altered outer membrane permeability

Klebsiella pneumoniae strains resistant to cefotaxime, ceftazidime and cefepime, but susceptible to imipenem and meropenem, were isolated from blood samples from two patients. Following treatment with meropenem, K. pneumoniae strains with reduced susceptibilities to imipenem and meropenem were isolated from the patients' stools. PCR assays and DNA sequencing showed that all the strains contain blaCTX M 15•, SDS-PAGE analysis of the outer membrane proteins did not identify OmpK35 and OmpK36 in any of the strains. The carbapenem susceptible strains were OmpK37 sufficient; however, this protein was not apparent in the strains with reduced susceptibility to carbapenems. It was concluded that resistance to extended spectrum β-lactams in the K. pneumoniae strains was due to the production of CTX-M-15, and reduced susceptibility to carbapenems was attributed to a combination of CTX-M and altered outer membrane permeability.