The Genera Aeromonas and Plesiomonas
Traditionally the genera Aeromonas and Plesiomonas have been considered together. Three international workshops (International Workshop, 1986 , 1988 , 1990 ) have considered many different aspects of these two genera. In addition, the two genera are usual
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The Genera Aeromonas and Plesiomonas J. J. FARMER III, M. J. ARDUINO AND F. W. HICKMAN-BRENNER
Traditionally the genera Aeromonas and Plesiomonas have been considered together. Three international workshops (International Workshop, 1986, 1988, 1990) have considered many different aspects of these two genera. In addition, the two genera are usually included in the same chapter or review (von Graevenitz, 1985). Only recently, however, has the relationship of the two genera been studied with methods that measure evolutionary distance. Although Aeromonas and Plesiomonas are not closely related, we have taken the traditional approach and considered them together in this chapter. However, we have separated most of our discussion because their differences seem more important than their similarities.
The Genus Aeromonas The genus Aeromonas has been known to microbiologists for many years. Most of the early literature was about diseases of frogs, fish, and other animals. Aeromonas is now recognized as an important opportunistic pathogen of humans; however, there is a controversy on the role of Aeromonas as a cause of human diarrhea. Through 1989, there were 1,436 literature citations for Aeromonas in the Medline computer data base and 2,589 citations in BIOSIS, so the reader interested in a particular aspect can use a computer literature search as a starting point.
History, Nomenclature, and Classification of Aeromonas The nomenclature and classification of the genus Aeromonas has been in a state of flux since these organisms were first described in the early 1890s and it is often difficult to know which Aeromonas species (in today’s usage) a particular article in the literature deals with. We have divided the history of Aeromonas into three different time periods. In the period 1890–1936, many different names were proposed for the Aeromonas strains isolated from a wide variety of sources and disThis chapter was taken unchanged from the second edition.
eases. In the period 1936–1979, the genus Aeromonas as we know it today was established, and many of the described species were studied and compared using techniques that measure phenotypic similarities and differences, but not evolutionary distance. Since 1979, techniques that measure evolutionary distance have been used to compare the species and to determine their relationship to other bacteria. These techniques have yielded some surprising results that form the basis of a more logical classification for the genus Aeromonas.
Aeromonas from 1890 to 1936 The first description of an organism that is now known to be an authentic Aeromonas species perhaps was that of Bacillus hydrophilus fuscus by Sanarelli (1891). Sanarelli (1891) was studying immunity to the anthrax bacillus in frogs, but many of his animals developed a septicemia that was not caused by the anthrax bacillus. Sanarelli isolated the causative bacterium and named it B. hydrophilus fuscus. Other Aeromonas-like organisms were also described during this period
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