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Antimicrobial Agents and Chemotherapy, June 2007, p. 1918-1925, Vol. 51, No. 6
0066-4804/07/$08.00+0     doi:10.1128/AAC.01500-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

External Guide Sequences Targeting the aac(6')-Ib mRNA Induce Inhibition of Amikacin Resistance

Alfonso J. C. Soler Bistué,^1, Hongphuc Ha,^2, Renee Sarno,² Michelle Don,^1,2 Angeles Zorreguieta,¹ and Marcelo E. Tolmasky^2*

Fundación Instituto Leloir, CONICET and Departamento de Química Biológica, FCEyN, University of Buenos Aires, Patricias Argentinas 435, C1405BWE Buenos Aires, Argentina,¹ Department of Biological Science, College of Natural Sciences and Mathematics, California State University Fullerton, Fullerton, California 92834-6850²

Received 29 November 2006/ Returned for modification 15 January 2007/ Accepted 14 March 2007

The dissemination of AAC(6')-I-type acetyltransferases have rendered amikacin and other aminoglycosides all but useless in some parts of the world. Antisense technologies could be an alternative to extend the life of these antibiotics. External guide sequences are short antisense oligoribonucleotides that induce RNase P-mediated cleavage of a target RNA by forming a precursor tRNA-like complex. Thirteen-nucleotide external guide sequences complementary to locations within five regions accessible for interaction with antisense oligonucleotides in the mRNA that encodes AAC(6')-Ib were analyzed. While small variations in the location targeted by different external guide sequences resulted in big changes in efficiency of binding to native aac(6')-Ib mRNA, most of them induced high levels of RNase P-mediated cleavage in vitro. Recombinant plasmids coding for selected external guide sequences were introduced into Escherichia coli harboring aac(6')-Ib, and the transformant strains were tested to determine their resistance to amikacin. The two external guide sequences that showed the strongest binding efficiency to the mRNA in vitro, EGSC3 and EGSA2, interfered with expression of the resistance phenotype at different degrees. Growth curve experiments showed that E. coli cells harboring a plasmid coding for EGSC3, the external guide sequence with the highest mRNA binding affinity in vitro, did not grow for at least 300 min in the presence of 15 µg of amikacin/ml. EGSA2, which had a lower mRNA-binding affinity in vitro than EGSC3, inhibited the expression of amikacin resistance at a lesser level; growth of E. coli harboring a plasmid coding for EGSA2, in the presence of 15 µg of amikacin/ml was undetectable for 200 min but reached an optical density at 600 nm of 0.5 after 5 h of incubation. Our results indicate that the use of external guide sequences could be a viable strategy to preserve the efficacy of amikacin.

Published ahead of print on 26 March 2007.

A.J.C.S.B. and H.H. contributed equally to this study.

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