The Genus Enterobacter
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The Genus Enterobacter FRANCINE GRIMONT AND PATRICK A.D. GRIMONT
Introduction The genus Enterobacter was first proposed by Hormaeche and Edwards (1960a). However, the history of some species now placed in the genus Enterobacter can be traced, albeit with some confusion, to the end of the 19th century. “Bacillus lactis aerogenes” was isolated by Escherich (1885) from milk and renamed “Bacillus aerogenes” by Kruse (1896) and “Aerobacter aerogenes” by Beijerinck (1900). Until 1955, differentiation of this organism from Friedländer’s bacillus (now called Klebsiella pneumoniae) was not clear, and most authors considered “B. lactis aerogenes” or “Aerobacter aerogenes” to be either nonmotile or to contain both motile and nonmotile strains (Grimbert and Legros, 1900; Edwards and Fife, 1955). This led Edwards and Fife (1955) to state that “A. aerogenes” strains were in fact Klebsiella strains. “Bacterium cloacae” was described by Jordan (1890) and transferred to a new genus “Cloaca” as “Cloaca cloacae” by Castellani and Chalmers (1920). In the first edition of Bergey’s Manual (Bergey et al., 1923), this species was transferred to the genus “Aerobacter” as “A. cloacae.” Since “Aerobacter aerogenes” was at that time indistinguishable from Klebsiella pneumoniae, Edwards and Fife (1955) proposed that the species “A. aerogenes” not be used, although disappearance of the type species (“A. aerogenes”) implied disappearance of the genus (“Aerobacter”). Because of this, two solutions were suggested for “A. cloacae”: 1) the reintroduction of the genus “Cloaca” with the species “Cloaca cloacae” (reference is not an exact match Kauffman, 1954); and 2) the redefinition of the genus “Aerobacter” with “A. cloacae” as type species (Edwards and Fife, 1955). However, this latter proposal did not conform to the rules of nomenclature. A significant step forward occurred when Møller (1955) devised some simple methods for testing amino acid decarboxylases. Since the “Cloaca” group was arginine-positive it could
This chapter was taken unchanged from the second edition.
now easily be distinguished from the Klebsiella group, which was arginine-negative. This led to the finding of motile strains of the “Cloaca” group, which were arginine-negative and produced gas from inositol and glycerol (Hormaeche and Munilla, 1957). These strains were called “Cloaca B” (arginine-positive strains forming the “Cloaca A group”). Then, after reexamination of many cultures using the decarboxylase test, Hormaeche and Edwards (1958) redefined the genus “Aerobacter” to include two species, “A. aerogenes” (“Cloaca B”) and “A. cloacae” (“Cloaca A”), with the type species reaffirmed as “A. aerogenes.” Grimes and Hennerty (1931) described a group of strongly proteolytic strains they named “Aerobacter liquefaciens.” However, this name was illegitimate since the same name had been used by Beijerinck (1900) for bacteria which could have been aeromonads, so that Grimes (1961) renamed his group as “Aerobacter lipolyticus.” Eventually, however
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