The differentiation of Aerobacter aerogenes and Aerobacter cloacae.

Many attempts, based on biochemical properties, have been made to differentiate strains of the tribe Eschericheae-a biochemically heterogeneous collection of the Enterobacteriaceae-into genera. In the sixth edition of Bergey's Manual (Breed et al., 1948), these strains, if of animal origin, are classified into three genera: Escherichia, Aerobacter, and Klebsiella. The genus Aerobacter is subdivided into two species, Aerobacter aerogenes and Aerobacter cloacae. More recently Kauffmann (1951) has claimed that the Friedlander (Klebsiella), Aerobacter, and Aerogenes "types" belong to one common group, which should be termed Klebsiella, as according to the rules of nomenclature this name has priority over the other two terms. In this article, using biochemical and morphological criteria, the relationship between A. aerogenes and A. cloacae will be discussed. It is generally accepted that according to their action on gelatin, Aerobacter strains may be divided into nonliquefying A. aerogenes and gelatin liquefying A. cloacae. The latter are claimed to be the only Eschericheae strains which liquefy gelatin. Working with a few strains, Kligler (1914) found that A. aerogenes attacked glycerol whereas A. cloacae did not. Johnson and Levine (1917) stated that A. aerogenes differs from A. cloacae in that it forms gas from glycerol, is nonumotile, and rarely liquefies gelatin. Inositol was first used for the differentiation of Eschericheae strains by MacConkey (1905). Mackie (1921) observed absolute positive correlation between capsule formation, fermentation of inositol, and absence of motility, and Hay (1932) noted that the feature most characteristic of the mucosus capsulatus group (Ylebsiella), apart from capsulation, was its ability to ferment inositol, but that this was shared also by A.