Acinetobacter

Acinetobacter is a genus of bacteria, well known in soil, 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.

Laboratory diagnosis

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. It sometimes appears 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.

Treatment

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.

There have also been reports of success with amikacin, rifampin, minocycline and tigecycline. Further treatment requires synergistic combinations, the selection of which is a work in progress.