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Mechanisms of Resistance

Influence of Transcriptional Activator RamA on Expression of Multidrug Efflux Pump AcrAB and Tigecycline Susceptibility in Klebsiella pneumoniae

Alexey Ruzin, Melissa A. Visalli, David Keeney, Patricia A. Bradford
Alexey Ruzin
1Wyeth Research, Pearl River, New York
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  • For correspondence: ruzina@wyeth.com
Melissa A. Visalli
1Wyeth Research, Pearl River, New York
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David Keeney
1Wyeth Research, Pearl River, New York
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Patricia A. Bradford
1Wyeth Research, Pearl River, New York
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DOI: 10.1128/AAC.49.3.1017-1022.2005
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ABSTRACT

Tigecycline is an expanded broad-spectrum antibacterial agent that is active against many clinically relevant species of bacterial pathogens, including Klebsiella pneumoniae. The majority of K. pneumoniae isolates are fully susceptible to tigecycline; however, a few strains that have decreased susceptibility have been isolated. One isolate, G340 (for which the tigecycline MIC is 4 μg/ml and which displays a multidrug resistance [MDR] phenotype), was selected for analysis of the mechanism for this decreased susceptibility by use of transposon mutagenesis with IS903φkan. A tigecycline-susceptible mutant of G340, GC7535, was obtained (tigecycline MIC, 0.25 μg/ml). Analysis of the transposon insertion mapped it to ramA, a gene that was previously identified to be involved in MDR in K. pneumoniae. For GC7535, the disruption of ramA led to a 16-fold decrease in the MIC of tigecycline and also a suppression of MDR. Trans-complementation with plasmid-borne ramA restored the original parental phenotype of decreased susceptibility to tigecycline. Northern blot analysis revealed a constitutive overexpression of ramA that correlated with an increased expression of the AcrAB transporter in G340 compared to that in tigecycline-susceptible strains. Laboratory mutants of K. pneumoniae with decreased susceptibility to tigecycline could be selected at a frequency of approximately 4 × 10−8. These results suggest that ramA is associated with decreased tigecycline susceptibility in K. pneumoniae due to its role in the expression of the AcrAB multidrug efflux pump.

  • Copyright © 2005 American Society for Microbiology
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Influence of Transcriptional Activator RamA on Expression of Multidrug Efflux Pump AcrAB and Tigecycline Susceptibility in Klebsiella pneumoniae
Alexey Ruzin, Melissa A. Visalli, David Keeney, Patricia A. Bradford
Antimicrobial Agents and Chemotherapy Feb 2005, 49 (3) 1017-1022; DOI: 10.1128/AAC.49.3.1017-1022.2005

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Influence of Transcriptional Activator RamA on Expression of Multidrug Efflux Pump AcrAB and Tigecycline Susceptibility in Klebsiella pneumoniae
Alexey Ruzin, Melissa A. Visalli, David Keeney, Patricia A. Bradford
Antimicrobial Agents and Chemotherapy Feb 2005, 49 (3) 1017-1022; DOI: 10.1128/AAC.49.3.1017-1022.2005
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KEYWORDS

Bacterial Proteins
Klebsiella pneumoniae
Membrane Transport Proteins
minocycline

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