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Antimicrobial Agents and Chemotherapy, October 2009, p. 4200-4210, Vol. 53, No. 10
0066-4804/09/$08.00+0 doi:10.1128/AAC.00428-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.
Staphylococcus aureus Mutant Screen Reveals Interaction of the Human Antimicrobial Peptide Dermcidin with Membrane Phospholipids 
Min Li ,1,
,
Kevin Rigby,1,
Yuping Lai,1,
Vinod Nair,2
Andreas Peschel,3
Birgit Schittek,4 and
Michael Otto1*
Laboratory of Human Bacterial Pathogenesis, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland,1 Research Technologies Section, Microscopy Unit, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Hamilton, Montana,2 Cellular and Molecular Microbiology Unit, Medical Microbiology and Hygiene Department,3 Department of Dermatology, University of Tübingen, Tübingen, Germany4
Received 30 March 2009/ Returned for modification 15 May 2009/ Accepted 7 July 2009
Antimicrobial peptides (AMPs) form an important part of the innate host defense. In contrast to most AMPs, human dermcidin has an anionic net charge. To investigate whether bacteria have developed specific mechanisms of resistance to dermcidin, we screened for mutants of the leading human pathogen, Staphylococcus aureus, with altered resistance to dermcidin. To that end, we constructed a plasmid for use in mariner-based transposon mutagenesis and developed a high-throughput cell viability screening method based on luminescence. In a large screen, we did not find mutants with strongly increased susceptibility to dermcidin, indicating that S. aureus has no specific mechanism of resistance to this AMP. Furthermore, we detected a mutation in a gene of unknown function that resulted in significantly increased resistance to dermcidin. The mutant strain had an altered membrane phospholipid pattern and showed decreased binding of dermcidin to the bacterial surface, indicating that dermcidin interacts with membrane phospholipids. The mode of this interaction was direct, as shown by assays of dermcidin binding to phospholipid preparations, and specific, as the resistance to other AMPs was not affected. Our findings indicate that dermcidin has an exceptional value for the human innate host defense and lend support to the idea that it evolved to evade bacterial resistance mechanisms targeted at the cationic character of most AMPs. Moreover, they suggest that the antimicrobial activity of dermcidin is dependent on the interaction with the bacterial membrane and might thus assist with the determination of the yet unknown mode of action of this important human AMP.
* Corresponding author. Mailing address: Laboratory of Human Bacterial Pathogenesis, National Institute of Allergy and Infectious Diseases, Building 33 1W10, 9000 Rockville Pike, Bethesda, MD 20892. Phone: (301) 443-5209. Fax: (301) 480-3633. E-mail: motto{at}niaid.nih.gov
Published ahead of print on 13 July 2009.
These authors contributed equally to the study.
Present address: Department of Laboratory Medicine, Huashan Hospital, Shanghai Medical College, Fudan University, 12 Central Urumqi Road, Shanghai 200040, People's Republic of China.
Present address: Division of Dermatology, University of California at San Diego, 3350 La Jolla Village Drive, San Diego, CA.
Antimicrobial Agents and Chemotherapy, October 2009, p. 4200-4210, Vol. 53, No. 10
0066-4804/09/$08.00+0 doi:10.1128/AAC.00428-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.
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