Chapter I _]7_ Taxonomy 



A detailed discussion of the various species that have so far been 

 described among the actinomycetes, based upon the classification of the 

 organisms into four genera is presented in the latest edition of Bergey's 

 Manual (34). Additional species not included in this Manual are 

 found in Krassilnikov's guide (236). The various principles upon 

 which the recognition of individual species are based are outlined here. 

 A description of the type species within each genus is also presented. 



Identification of Actinomycetes:— To identify certain individual 

 species of actinomycetes, it is sufficient to give recognition to some of 

 their characteristic properties. These are based upon the occurrence 

 of these organisms in their natural substrates, upon their morphology, 

 upon their cultural characteristics, and upon their biochemical proper- 

 ties. 



Ecology as a basis of classification.— Although various attempts have 

 been made to classify actinomycetes into several groups on the basis 

 of their natural habitats, no broad system for generalization can ever be 

 developed on this basis alone. It is true that the anaerobic forms, de- 

 scribed here under the genus Actinomyces are largely animal pathogens, 

 and that some of the Nocardia species are also pathogenic. It is also 

 true that the Streptomyces group is characteristic of soils and that the 

 Micro-inonosfora types are found in high-temperature composts, as well 

 as in river and lake waters and bottoms. This alone is hardly sufficient 

 for a separation of the organisms on the basis of their natural occurrence. 

 Such a division would be arbitrary and only approximately true. 



It has been suggested (250), for example, that the disease-producing 

 actinomycetes be classified on the basis of the specific type of disease; 

 namely, 1. anaerobes, of the Wolf-Israejl type, that attack the abdo- 

 men; 2. aerobes that cause actinomycosis of the lungs, including sapro- 

 phytes occurring in the dust; 3. forms causing swellings in the infectious 

 area, organisms said to be of the so-called Streptothrix type. 



Actinomycetes are universally present in water basins, in soils, in 

 milk, in or upon other foodstuffs, and in dust. Many attempts have 

 been made to divide these groups upon the basis of their specific habitats. 

 The soil forms, for example, have been separated into plant pathogens 

 and saprophytes; the food-inhabiting types, into odoriferous and non- 

 odoriferous types. These separations, like those based on natural oc- 

 currence, were quite arbitrary. The cosmopolitan nature of many 

 actinomycetes is well established, since species found in one part of 

 the world, are soon discovered also in other parts. Species found in 

 soils may also be found in peats or on foodstuffs. Thus ecology can 

 hardly be considered as a major basis for the classification of actinomy- 

 cetes. 



Morphology as a hasis for classification.— Ahhough morphological 

 characters are used for the separation of the broader groups of actinomy- 

 cetes, the families and genera, they can also be utilized for the subdivi- 



