Acinetobacter baumannii

Acinetobacter baumannii is a typically short, almost round, rod-shaped (coccobacillus) 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 (nosocomial) infection. While other species of the genus Acinetobacter are often found in soil samples (leading to the common misconception that A. baumannii is a soil organism, too), 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.

Bacteria of this genus lack flagella but exhibit twitching or swarming motility, likely mediated by type IV pili. Motility in A. baumannii may also be due to the excretion of exopolysaccharide, creating a film of high-molecular-weight sugar chains behind the bacterium to move forward. Clinical microbiologists typically differentiate members of the genus Acinetobacter from other Moraxellaceae by performing an oxidase test, as Acinetobacter spp. are the only members of the Moraxellaceae to lack cytochrome c oxidases. A. baumannii is strictly aerobic, meaning it needs oxygen to grow. Although studies have shown that A. Baumannii is able to survive in varying levels of oxygen, including no oxygen, by entering a dormant state.