HEALTHY skin has a specialised chemical defence mechanism that selectively targets the common gut bacterium Escherichia coli.
E. coli cannot survive for long on healthy skin but can infect burnt or damaged skin. So Jens-Michael Schr枚der of the University Hospital Schleswig-Holstein in Kiel, Germany, was keen to find out what was killing the bacteria. 鈥淚nfection of skin is a rare event,鈥� says Schr枚der, 鈥渨e want to know why.鈥�
Schr枚der鈥檚 team tested skin proteins until they found one called psoriasin that killed E. coli but left other skin bacteria unharmed. To prove the protein was responsible, the team blocked psoriasin鈥檚 action by adding antibodies that bind to it. Sure enough, the killing effect went away. The protein is particularly concentrated on the scalp, face and soles of the feet.
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Psoriasin kills bacteria in a completely different way to other skin antibacterials, says Schr枚der. The protein mops up zinc ions, which E. coli needs to counteract damage from oxidising chemicals. Without these, damage to proteins and DNA accumulates, eventually killing the cell. When the team added extra zinc ions, the killing power of the protein dropped off (Nature Immunology, DOI: 10.1038/ni1142).
Schr枚der hopes eventually to use artificial psoriasin to prevent E. coli infection in patients with damaged, cracked or burnt skin.