Acinetobacter baumannii

Acinetobacter baumannii
Scientific classification
Domain:	Bacteria
Phylum:	Pseudomonadota
Class:	Gammaproteobacteria
Order:	Pseudomonadales
Family:	Moraxellaceae
Genus:	Acinetobacter
Species:	A. baumannii
Binomial name
Acinetobacter baumannii Bouvet and Grimont 1986[1]

Acinetobacter baumannii is a typically short, almost round, rod-shaped (coccobacillus) Gram-negative bacterium. It is named after the bacteriologist Paul Baumann.^[2] 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.^[3] Although occasionally it has been found in environmental soil and water samples,^[4] its natural habitat is still not known.^{[citation needed]}

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.^[5] 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.^[6]

A. baumannii is part of the ACB complex (A. baumannii, A. calcoaceticus, and Acinetobacter genomic species 13TU). It is difficult to determine the specific species of members of the ACB complex and they comprise the most clinically relevant members of the genus.^[7][8] A. baumannii has also been identified as an ESKAPE pathogen (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter species), a group of pathogens with a high rate of antibiotic resistance that are responsible for the majority of nosocomial infections.^[9]

Colloquially, A. baumannii is referred to as "Iraqibacter" due to its seemingly sudden emergence in military treatment facilities during the Iraq War.^[10] It has continued to be an issue for veterans and soldiers who served in Iraq and Afghanistan. Multidrug-resistant A. baumannii has spread to civilian hospitals in part due to the transport of infected soldiers through multiple medical facilities.^[5] During the COVID-19 pandemic, coinfection with A. baumannii secondary to SARS-CoV-2 infections has been reported multiple times in medical publications.^[11]