title: Rapid induction of high-level carbapenem resistance in heteroresistant KPC-producing Klebsiella pneumoniae.
abstract: Enterobacteriaceae strains producing the Klebsiella pneumoniae carbapenemase (KPC) have disseminated worldwide, causing an urgent threat to public health. KPC-producing strains often exhibit low-level carbapenem resistance, which may be missed by automated clinical detection systems. In this study, eight Klebsiella pneumoniae strains with heterogeneous resistance to imipenem were used to elucidate the factors leading from imipenem susceptibility to high-level resistance as defined by clinical laboratory testing standards. Time-kill analysis with an inoculum as low as 3 × 10(6) CFU/ml and concentrations of imipenem 8- and 16-fold higher than the MIC resulted in the initial killing of 99.9% of the population. However, full recovery of the population occurred by 20 h of incubation in the same drug concentrations. Population profiles showed that recovery was mediated by a heteroresistant subpopulation at a frequency of 2 × 10(-7) to 3 × 10(-6). Samples selected 2 h after exposure to imipenem were as susceptible as the unexposed parental strain and produced the major outer membrane porin OmpK36. However, between 4 to 8 h after exposure, OmpK36 became absent, and the imipenem MIC increased at least 32-fold. Individual colonies isolated from cultures after 20 h of exposure revealed both susceptible and resistant subpopulations. Once induced, however, the high-level imipenem resistance was maintained, and OmpK36 remained unexpressed even without continued carbapenem exposure. This study demonstrates the essential coordination between blaKPC and ompK36 expression mediating high-level imipenem resistance from a population of bacteria that initially exhibits a carbapenem-susceptibility phenotype.
authors: School of Public Health, Division of Infectious Diseases and Vaccinology, University of California, Berkeley, Berkeley, California, USA.
authors: Sheila
authors: S
authors: Adams-Sapper
authors: School of Public Health, Division of Infectious Diseases and Vaccinology, University of California, Berkeley, Berkeley, California, USA.
authors: Shantell
authors: S
authors: Nolen
authors: School of Public Health, Division of Infectious Diseases and Vaccinology, University of California, Berkeley, Berkeley, California, USA.
authors: Grace Fox
authors: GF
authors: Donzelli
authors: School of Public Health, Division of Infectious Diseases and Vaccinology, University of California, Berkeley, Berkeley, California, USA.
authors: Mallika
authors: M
authors: Lal
authors: School of Public Health, Division of Infectious Diseases and Vaccinology, University of California, Berkeley, Berkeley, California, USA.
authors: Kunihiko
authors: K
authors: Chen
authors: Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil.
authors: Livia Helena
authors: LH
authors: Justo da Silva
authors: Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil.
authors: Beatriz M
authors: BM
authors: Moreira
authors: School of Public Health, Division of Infectious Diseases and Vaccinology, University of California, Berkeley, Berkeley, California, USA lwriley@berkeley.edu.
authors: Lee W
authors: LW
authors: Riley
mesh_terms: D001425:Bacterial Outer Membrane Proteins / Q000235:genetics / Q000378:metabolism; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D015780:Carbapenems / Q000494:pharmacology*; D015378:Imipenem; D007711:Klebsiella pneumoniae / Q000187:drug effects* / Q000201:enzymology* / Q000235:genetics; D008826:Microbial Sensitivity Tests; D060888:Real-Time Polymerase Chain Reaction; D020133:Reverse Transcriptase Polymerase Chain Reaction; D021241:Spectrometry, Mass, Electrospray Ionization; D001618:beta-Lactamases / Q000235:genetics / Q000378:metabolism*
chemical_list: D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D015780:Carbapenems; D015378:Imipenem; D001618:beta-Lactamases; C063912:carbapenemase