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Antimicrobial Agents and Chemotherapy, November 2007, p. 3836-3843, Vol. 51, No. 11
0066-4804/07/$08.00+0     doi:10.1128/AAC.00722-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Functional Characterization of TcaA: Minimal Requirement for Teicoplanin Susceptibility and Role in Caenorhabditis elegans Virulence{triangledown}

Nadine McCallum,1* Ann Karen C. Brassinga,2 Costi D. Sifri,2 and Brigitte Berger-Bächi1

Institute of Medical Microbiology, University of Zurich, Gloriastr. 32, 8006 Zurich, Switzerland,1 Division of Infectious Diseases and International Health, University of Virginia Health System, P.O. Box 801361, Charlottesville, Virginia 229082

Received 5 June 2007/ Returned for modification 24 July 2007/ Accepted 10 August 2007

The inactivation of TcaA contributes to intrinsic teicoplanin resistance in experimental and clinical isolates of glycopeptide-intermediate resistant Staphylococcus aureus. PhoA fusions confirmed that TcaA is a transmembrane protein with a short intracellular N-terminal domain containing a C-4 zinc finger binding motif, a single membrane-spanning domain, and a large extracellular C-terminal domain. The region conferring teicoplanin susceptibility was narrowed down to the transmembrane part and the first third of the extracellular domain of TcaA, suggesting that neither the C-4 zinc finger binding motif nor the C terminus contributed to teicoplanin susceptibility. TcaA belongs to the cell wall stress stimulon, which comprises a set of genes universally upregulated by cell wall damage. Induction of tcaA was shown to be fully dependent on the two-component regulatory system VraSR. A 66-bp region upstream of the transcriptional start site, which contained an inverted repeat partially covering the promoter box, was shown to be essential for VraSR-mediated induction by cell wall stress. Interestingly, the induction or overexpression of tcaA did not contribute further to teicoplanin susceptibility, suggesting that small amounts of TcaA, such as those present under normal uninduced conditions, were sufficient for TcaA-mediated teicoplanin susceptibility. The strong attenuation of tcaA deletion mutants in a Caenorhabditis elegans survival assay suggested that TcaA may, in addition to affecting glycopeptide susceptibility, also play a role in virulence.

* Corresponding author. Mailing address: Institute of Medical Microbiology, University of Zurich, Gloriastr. 32, 8006 Zurich, Switzerland. Phone: 41 44 634 2694. Fax: 41 44 634 4906. E-mail: mccallum{at}immv.uzh.ch

{triangledown} Published ahead of print on 20 August 2007.

Antimicrobial Agents and Chemotherapy, November 2007, p. 3836-3843, Vol. 51, No. 11
0066-4804/07/$08.00+0     doi:10.1128/AAC.00722-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.



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