[Black nails caused by Proteus mirabilis].

Black nails caused by Proteus mirabilis were seen in a motor mechanic and in a petrol pump attendant. Proteus mirabilis is a gram-negative bacillus that generates hydrogen sulfide. This compound reacts with traces of metals in the nail plate such as zinc, nickel, cobalt, iron, manganese, tin, copper and lead. Metal sulfides blacken the nail plate. The protracted course of the discoloration over months corresponds to the slow reactions of metals with hydrogen sulfide. The disappearance of the blackening after topical treatment with chinosol, tincture of iodine and chloramphenicol solution supports the etiologic connection between black nails and Proteus mirabilis. Wet and dirty work encourages the colonisation of Proteus mirabilis between nail fold and nail plate.