http://bmj.com/cgi/content/full/323/7323/1206/c

BMJ 2001;323:1206 ( 24 November )

News roundup

Bacteria killer found in sweat

Deborah Josefson San Francisco

Human sweat is capable of warding off more than potential friends and lovers.

Researchers at Eberhard-Karls University in Tübingen, Germany, have isolated a new antibiotic, dubbed dermcidin, which is secreted in sweat and may serve as a first line of defence against microbial pathogens.

Dermcidin’s structure differs from known antibiotics and may kill micro-organisms by a different mechanism. The work has been published in the online edition of Nature Immunology (www.nature.com/ni) in advance of the print edition.

Dr Birgit Schittek and her colleagues from the university’s departments of oncological dermatology, immunology, molecular biology, and genetics stumbled serendipitously on the dermcidin gene while screening DNA libraries from melanoma and naevus cell lines. They found a previously unidentified gene sequence among the clones and decided to characterise it. The scientists localised the gene to chromosome 12 and found it coded for a peptide whose expression was limited to the skin.

Immunohistochemical and in situ hybridisation techniques showed that expression is preferentially restricted to eccrine sweat glands and is found in mucous cells of the sweat gland coil as well as in the secretory granules in Golgi’s complex.

These findings suggested that the protein is secreted in sweat, so the team tested perspiration for dermcidin’s presence. They isolated sweat protein fractions taken from four volunteers and sequenced the resultant fractions. Among the proteins isolated was a 47 kilodalton processed form of the dermcidin peptide.

As the size of the protein was similar to that of defensins, another group of peptides secreted by skin cells that exhibit antimicrobial activity, the researchers tested whether dermcidin also possessed such properties. It turned out to be active against both gram positive and gram negative bacteria as well as some against yeast species.

Dermcidin killed Escherichia coli, Enterococcus faecalis, Staphylococcus aureus, and Candida albicans. It was active at high salt concentrations and the acidity range of human sweat, where it was present at concentrations of 1-10 m g/ml. It was active against E coli and E faecalis at a minimum inhibitory concentration of 1 m g/ml and against S aureus and C albicans at 10 m g/ml. Incubation at this concentration killed all of the S aureus colonies in only four hours. Bactericidal activity increased with dermcidin concentration and time.

The team showed that dermcidin was killing the bacteria by testing the other protein fractions derived from the sweat as controls. They found that these components lacked antibiotic properties.

Dermcidin’s structure differs from known antibiotics and may represent a previously unknown family of proteins with antimicrobial activity. Unlike the defensins, which are made by keratinocytes in response to inflammation, dermcidin is produced all the time and seems to be secreted constantly in sweat. Moreover, the peptide has a negative charge whereas many known antibiotics are positively charged and produce their antimicrobial effect by punching pores into bacterial cell membranes.

Dr Schittek acknowledged that her team does not yet know how dermcidin works. She suggested that "it probably plays a key role in the innate immune responses of the skin" and speculated that differing levels of dermcidin expression may have a role in patients with skin disorders such as eczema and atopic dermatitis, as these patients get frequent skin infections. The group plans to test dermcidin against various viruses to see if it also has antiviral activity.
 
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