Cutaneous infection caused by Serratia marcescens

An 86-year-old woman presented with a chronic granulomatous skin lesion on the dorsal aspect of her left hand. Histologic examination showed pseudoepitheliomatous hyperplasia and a dense dermal infiltrate largely composed of lymphocytes and histiocytes. Abscess formation and fibroblastic proliferation were also present. Use of Fite, Giemsa, and periodic acid-Schiff stains did not show specific organisms. The gram-negative bacillus Serratia marcescens was the only microorganism isolated from all cultures performed. Trimethoprim-sulfamethoxazole, 960 mg every 12 hours for 20 days (orally), was given and resulted in complete disappearance of the lesion and negative culture findings. Cutaneous infection by S marcescens may represent a distinctive entity, whose clinical and possible pathogenic features are presented here.