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VmeAB, an RND-type multidrug efflux transporter in Vibrio parahaemolyticus

Taira Matsuo^1,

Katsuhiko Hayashi^2,

Yuji Morita^2,

Tohru Mizushima^2,

¹ Department of Genome Applied Microbiology, Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama University, Tsushima, Okayama 700-8530, Japan
² Department of Molecular Microbiology, Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama University, Tsushima, Okayama 700-8530, Japan

Correspondence
Teruo Kuroda
tkuroda{at}cc.okayama-u.ac.jp

Genes vmeA and vmeB, encoding a multidrug efflux transporter in the halophilic bacterium Vibrio parahaemolyticus, have been cloned using a drug-hypersusceptible Escherichia coli strain as the host. Cells of E. coli KAM33 (acrAB ydhE) carrying the vmeAB region from V. parahaemolyticus conferred much higher MICs for a variety of antimicrobial agents than did control cells. Cells possessing VmeAB under energized conditions maintained very low intracellular concentrations of ethidium. This was as expected for an energy-dependent efflux system, and supports the notion – based on sequence homology – that VmeAB belongs to the resistance nodulation cell division (RND) family of multidrug efflux transporters. It is likely that VmeAB forms functional complexes with the outer-membrane protein TolC in E. coli, because introduction of vmeAB into cells of E. coli KAM43, which lacks the tolC gene, failed to elevate the MICs for any of the antimicrobial agents tested. Therefore, a V. parahaemolyticus homologue of tolC was also cloned, designated vpoC, and was introduced together with vmeAB into cells of E. coli KAM43. The MICs of all agents tested were raised and were comparable to the values observed in E. coli KAM33 harbouring a plasmid carrying vmeAB. Finally, a vmeAB-deficient mutant of V. parahaemolyticus was constructed (designated TM3). TM3 showed slightly higher susceptibility than the parental V. parahaemolyticus to some antimicrobial agents. Survival rate of the TM3 when exposed to deoxycholate decreased compared with that of the parent.

These authors contributed equally to this work.

Present address: Department of Microbiology, School of Pharmacy, Aichi Gakuin University, Nagoya 464-8650, Japan.

Present address: Graduate School of Medical and Pharmaceutical Sciences. Kumamoto University, Kumamoto 862-0973, Japan.

The GenBank/EMBL/DDBJ accession number for the sequence reported in this paper is AB251606 (vmeAB).