Acinetobacter baumannii is a typically short, almost round, rod-shaped Gram-negative bacterium. It is named after the bacteriologist Paul Baumann. It can be an opportunistic pathogen in humans, affecting people with compromised immune systems, and is becoming increasingly important as a hospital-derived infection. While other species of the genus Acinetobacter are often found in soil samples , it is almost exclusively isolated from hospital environments. Although occasionally it has been found in environmental soil and water samples, its natural habitat is still not known.[citation needed]