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 as 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.