Value of Pigmentation in Classifying Actinomycetes

Abstract

The genus Actinomyces is generally regarded as lying between the true bacteria and higher fungi, and contains a few parasitic species but many saprophytic forms. The latter occur mostly in the soil and many of them produce striking pigments. It is quite natural that efforts have been made to utilize these pigments in the identification of species; but the present unsatisfactory nature of the classification of this group suggests that-striking though these pigments are-they have not proved of great diagnostic value. The first attempt to use pigmentation in classifying the organisms resulted in the recognition of two groups which were at that time considered species and were named by Gasperini Actinomyces albus and A. chromogenus respectively. The former was supposed to produce no pigmentation and the latter to cause a browning of the medium in which it was grown. The early work on which this classification was based was done with the use of media containing peptone or gelatin. It has since been shown that if the soil Actinomycetes are grown on synthetic media this particular brown pigment is never produced, but instead much brighter colors occur and species can be obtained showing nearly all the primary colors of the rainbow. On such media as