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Inhibition of Gene Expression and Growth by Antisense Peptide Nucleic Acids in a Multiresistant ß-Lactamase-Producing Klebsiella pneumoniae Strain

Department of Microbiology, Yong Loo Lin School of Medicine, National University of Singapore, 5 Science Drive 2, Singapore 117597,¹ Department of Laboratory Medicine, National University Hospital, Kent Ridge, Singapore 119074, Singapore²

Received 8 June 2006/ Returned for modification 14 August 2006/ Accepted 1 December 2006

Klebsiella pneumoniae causes common and severe hospital- and community-acquired infections with a high incidence of multidrug resistance. The emergence and spread of ß-lactamase-producing K. pneumoniae strains highlight the need to develop new therapeutic strategies. In this study, we developed antisense peptide nucleic acids (PNAs) conjugated to the (KFF)₃K peptide and investigated whether they could mediate gene-specific antisense effects in K. pneumoniae. No outer membrane permeabilization was observed with antisense PNAs when used alone. Antisense peptide-PNAs targeted at two essential genes, gyrA and ompA, were found to be growth inhibitory at concentrations of 20 µM and 40 µM, respectively. Mismatched antisense peptide-PNAs with sequence variations of the gyrA and ompA genes when used as controls were not growth inhibitory. Bactericidal effects exerted by peptide-anti-gyrA PNA and peptide-anti-ompA PNA on cells were observed within 6 h of treatment. The antisense peptide-PNAs specifically inhibited expression of DNA gyrase subunit A and OmpA from the respective targeted genes in a dose-dependent manner. Both antisense peptide-PNAs cured IMR90 cell cultures that were infected with K. pneumoniae (10⁴ CFU) in a dose-dependent manner without any noticeable toxicity to the human cells.

Published ahead of print on 11 December 2006.