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JAC Advance Access published online on March 10, 2005
Journal of Antimicrobial Chemotherapy, doi:10.1093/jac/dki070
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JAC © The British Society for Antimicrobial Chemotherapy 2005; all rights reserved
Received July 19, 2004
Revised January 19, 2005
Accepted January 22, 2005

Original article

In vitro resistance to the CS{alpha}{beta}-type antimicrobial peptide ASABF- is conferred by overexpression of sigma factor sigB in Staphylococcus aureus

Hong Zhang 1, Kazuya Morikawa 2, Toshiko Ohta 2, and Yusuke Kato 1*

1 Department of Developmental Biology, National Institute of Agrobiological Sciences, Oowashi 1-2, Tsukuba, Ibaraki 305-8634, Japan
2 Institute of Basic Medical Sciences, Graduate School of Comprehensive Human Sciences, University of Tsukuba, Tennoudai 1-1-1, Tsukuba, Ibaraki 305-8577, Japan

* To whom correspondence should be addressed.
Yusuke Kato, E-mail: kato{at}affrc.go.jp


  Abstract

Objectives: ASABF (Ascaris suum antibacterial factor) is a CS{alpha}{beta}-type antimicrobial peptide isolated from nematodes. ASABF-, a member of ASABF, is particularly effective against the Gram-positive pathogen Staphylococcus aureus. In this study, we investigated the role of sigB expression on ASABF-resistance in S. aureus.

Methods: Based on preliminary characterization of the ASABF-resistant strain, Mu50, we speculated that the alternative sigma factor sigB may regulate resistance against antimicrobial peptides. To test this hypothesis, the ASABF susceptibility was compared between NKSB (a sigB-knockout derivative of N315) and its sigB-overexpressing derivative. In addition, similar experiments were carried out for N315ex, a deletion mutant of N315 for SCCmec (Staphylococcus cassette chromosome mec) which contains essential genes for {beta}-lactam resistance.

Results: The sigB-overexpressing NKSB acquired an increased resistance to ASABF- compared with the parent strain. The sigB-induced ASABF- resistance was also observed in N315ex.

Conclusions: The overexpression of sigB confers resistance to the antimicrobial peptide, ASABF-. SCCmec is not essential for this resistance.

Keywords: Caenorhabditis elegans; Ascaris suum; stress response; defensin; antibiotics; CS{alpha}{beta} motif.
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