Acinetobacter is a genus of bacteria, well known in soil, not uncommon in the mouth, but increasingly as a human and animal pathogen, and displaying multidrug resistance. Acinetobacter baumanii is the most problematic organism, which increasingly appears in multidrug-resistant forms. Resistant forms have also been a problem in Iraq and Afghanistan, and in hospital-acquired infections, especially in military hospitals.
Morphologically, they are non-motile coccobacilli, appearing in pairs. These diplococci are normally Gram-negative, but occasionally stain as Gram-positive. While they are encapsulated, the false positive Gram stain is not due to the classical mucopolysaccharides in the cell wall, but an organism-specific tendency to retain crystal violet dye. One review states it can appear as a bacillus, resembling Hemophilus influenzae.
They are oxidase-negative, non-fermentative and aerobic, able to grow on a wide range of routine culture media. 
Non-resistant forms are susceptible to a fairly wide range of antibiotics. For the most common multidrug-resistant forms, non-penicillin, non-cephalosporin beta lactam antibiotics of the carbapenem group, imipenem and meropenem. Carbapenem-resistant forms are being seen, and there has been some success with the toxic antibiotics colistin and polymyxin B. Resistance has been reported with the latter two drugs.
Epidemiologists have been aware of them as a nosocomial threat since the late 1990s. U.S. military hospitals, in particular, have had problems with nosocomial transfer. Several have established wards for isolating Acinetobacter patients.
- Burke A Cunha (19 October 2009), "Acinetobacter", eMedicine
- Lisa Maragakis, Multidrug-Resistant (MDR) Acinetobacter, Hospital Epidemiology/Infection Control, Johns Hopkins Medicine
- Infection Control Guidelines for New York State - Nosocomial Acinetobacter Infection, New York State Department of Health, August 1999
- Husni RN et al (May 1999), "Risk Factors for an Outbreak of Multi-Drug-Resistant Acinetobacter Nosocomial Pneumonia Among Intubated Patients*", Chest