MarA-mediated overexpression of the AcrAB efflux pump results in decreased susceptibility to tigecycline in Escherichia coli

• Published in: Journal of antimicrobial chemotherapy 2008-01, Vol.61 (1), p.46-53
• Main Authors: Keeney, David, Ruzin, Alexey, McAleese, Fionnuala, Murphy, Ellen, Bradford, Patricia A.
• Format: Article
• Language: English
• Subjects: Anti-Bacterial Agents - pharmacology; antibiotic resistance; Antibiotics. Antiinfectious agents. Antiparasitic agents; Bacterial Outer Membrane Proteins - biosynthesis; Bacterial Outer Membrane Proteins - genetics; Bacterial Proteins - biosynthesis; Bacterial Proteins - genetics; Base Sequence; Biological and medical sciences; Clinical trials; Deoxyribonucleic acid; DNA; DNA Transposable Elements - genetics; DNA-Binding Proteins - biosynthesis; DNA-Binding Proteins - genetics; Drug Resistance, Bacterial - drug effects; Drug Resistance, Bacterial - genetics; E coli; Escherichia coli; Escherichia coli - drug effects; Escherichia coli - genetics; Escherichia coli - isolation & purification; Escherichia coli - metabolism; Escherichia coli Proteins - biosynthesis; Escherichia coli Proteins - genetics; Frameshift Mutation; Gene expression; Lipoproteins - biosynthesis; Lipoproteins - genetics; Medical sciences; Membrane Transport Proteins - biosynthesis; Membrane Transport Proteins - genetics; Microbial Sensitivity Tests; Microbiology; Minocycline - analogs & derivatives; Minocycline - pharmacology; Molecular Sequence Data; multidrug efflux pump; Multidrug Resistance-Associated Proteins - biosynthesis; Multidrug Resistance-Associated Proteins - genetics; Mutation; Open Reading Frames; Pharmacology. Drug treatments; resistance nodulation cell division family; RNA, Bacterial - genetics; RT-PCR; transcriptional profile analysis
• ISSN: 0305-7453; 1460-2091
• DOI: 10.1093/jac/dkm397

Objectives The purpose of this study was to characterize decreased susceptibility to tigecycline in clinical isolates of Escherichia coli obtained during Phase 3 clinical trials. Methods Gene expression was analysed by transcriptional profile analysis and RT-PCR. Transposon mutagenesis with IS903ϕkan was used for selection of transposon mutants. Transposon insertions were mapped by DNA sequencing and PCR analyses. The MICs were determined by broth microdilution. Results Both transcriptional profile analysis and Taqman RT-PCR demonstrated increased expression levels of MarA, a transcriptional activator, and AcrAB, an RND-type efflux pump, in the strains with elevated tigecycline MICs. Transposon mutagenesis generated nine mutants, the majority of which had either marA or acrB inactivated. Sequence analysis revealed a single nucleotide insertion in the open reading frame of the marR gene in less-susceptible strains of E. coli. Conclusions This study suggested that a loss of MarR functionality due to a frameshift mutation resulted in constitutive overproduction of MarA and AcrAB and, consequently, in decreased susceptibility to tigecycline in clinical isolates of E. coli.