MODEL RELEASED. Infected skin graft. Opportunistic bacteria (Psuedomonas aeruginosa) infecting a skin graft. The toes were amputated because the tissue was destroyed by diabetic neuropathy and occulusive circulation. Psuedomonas aeruginosa is an opportunistic human pathogen that secretes a variety of pigments, including pyocyanin (blue- green) and pyorubin (red-brown). It is a Gram- negative bacteria and is naturally resistant to a large range of antibiotics such as penicillin. People suffering from diabetes often develop ulcers on the feet due to inadequate blood supply or neuropathy (nerve damage) caused by the disease. In severe cases, the ulcers can become gangrenous necessitating removal of the affected region.