Black nails from Proteus mirabilis colonisation

Black nails caused by Proteus mirabilis were seen in a motor mechanic and i n a petrol pump attendant. Proteus mirabilis is a gramnegative bacillus tha t 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 t he discoloration over months corresponds to the slow reactions of metals wi th hydrogen sulfide. The disappearance of the blackening after topical trea tment with chinosol, tincture of iodine and chloramphenicol solution suppor ts the etiologic connection between black nails and Proteus mirabilis. Wet and dirty work encourages the colonisation of Proteus mirabilis between nai l fold and nail plate.