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Antimicrobial Agents and Chemotherapy, April 2007, p. 1455-1462, Vol. 51, No. 4
0066-4804/07/$08.00+0     doi:10.1128/AAC.00348-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

rpoN Gene of Pseudomonas aeruginosa Alters Its Susceptibility to Quinolones and Carbapenems

Darija Viducic,^1, Tsuneko Ono,² Keiji Murakami,¹ Mikiko Katakami,² Heni Susilowati,¹ and Yoichiro Miyake^1*

Department of Microbiology, Institute of Health Biosciences, The University of Tokushima Graduate School, Tokushima 770-8504,¹ Department of Laboratory Science, School of Health Sciences, The University of Tokushima, Tokushima 770-8509, Japan²

Received 22 March 2006/ Returned for modification 18 July 2006/ Accepted 21 January 2007

The alternative sigma factor ⁵⁴ has been implicated in diverse functions within the cells. In this study, we have constructed an rpoN mutant of Pseudomonas aeruginosa and investigated its importance as a target for antimicrobial agents, such as quinolones and carbapenems. The stationary-phase cells of the rpoN mutant displayed a survival rate approximately 15 times higher than that of the wild-type cells in the presence of quinolones and carbapenems. The stationary phase led to substantial production of pyoverdine by the P. aeruginosa rpoN mutant. Pyoverdine synthesis correlated with decreased susceptibility to antimicrobial agents. Quantitative real-time PCR revealed that stationary-phase cells of the rpoN mutant grown without an antimicrobial agent had approximately 4- to 140- and 2- to 14-fold-higher levels of transcripts of the pvdS and vqsR genes, respectively, than the wild-type strain. In the presence of an antimicrobial agent, levels of pvdS and vqsR transcripts were elevated 400- and 5-fold, respectively, in comparison to the wild-type levels. Flow cytometry assays using a green fluorescent protein reporter demonstrated increased expression of the vqsR gene in the rpoN mutant throughout growth. A pvdS mutant of P. aeruginosa, deficient in pyoverdine production, was shown to be susceptible to biapenem. These findings suggest that rpoN is involved in tolerance to antimicrobial agents in P. aeruginosa and that its tolerant effect is partly dependent on increased pyoverdine production and vqsR gene expression.

Published ahead of print on 29 January 2007.

Present address: Department of Molecular Biology and Microbiology, Case Western Reserve University School of Medicine, Cleveland, OH 44106.