The Genus Acinetobacter
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The Genus Acinetobacter KEVIN TOWNER
Introduction Gram-negative nonfermentative bacteria belonging to the genus Acinetobacter have been classified previously under at least 15 different names (Bergogne-Bérézin and Towner, 1996), and it is only relatively recently that rational taxonomic proposals have emerged. Delineation of species is still the subject of ongoing research, and a rapid and reliable method of assigning new isolates to individual species is particularly needed. Notwithstanding the continuing taxonomic confusion, it is clear that acinetobacters are common, free-living saprophytes found in soil, water, sewage and foods. They are also ubiquitous organisms in the clinical environment, where they can be isolated as commensals from the skin of hospital staff and patients. They have increasingly been recognized as important nosocomial pathogens involved in outbreaks of hospital infection, particularly in high-dependency or intensive care units, where they rapidly develop resistance to even the most potent antimicrobials (Bergogne-Bérézin and Towner, 1996). Although the significant pathogenic role of Acinetobacter is largely confined to nosocomial infections, it is important to note that these organisms are ubiquitous in both the clinical and nonclinical environments. Their metabolic versatility means that they may play an important role in a variety of commercially important industrial processes, as well as in the biodegradation of a wide range of environmental pollutants. While much remains to be learned about the lifestyles of the different members of the genus, it is clear that some facets of their behavior are unique and others provide new insights into prokaryotic behavior in general. Members of the genus Acinetobacter have suffered a long history of extensive taxonomic change which has inhibited a proper appreciation and understanding of their significant biological properties and pathogenic importance. Although the delineation of species within the genus is still the subject of ongoing discussion and research, it appears that the current taxon-
omy should form a rational scientific foundation for the numerous important investigative studies required in the future.
Phylogeny Members of the genus Acinetobacter have historically been classified by various authors under a variety of different names (Bergogne-Bérézin and Towner, 1996) and consequently, much of the early literature concerning this group of organisms is difficult to interpret owing to confusion over phylogeny and the lack of a widely accepted classification scheme. The genus Acinetobacter, as originally proposed in 1954, included a heterogeneous collection of nonmotile Gramnegative saprophytes that could be distinguished from other similar bacteria by their lack of pigmentation. The Subcommittee on the Taxonomy of Moraxella and Allied Bacteria subsequently proposed in 1971 that the genus Acinetobacter should include only the oxidase-negative strains, and this division has been supported by the use of
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