SUMMARY: The taxonomic position of organisms belonging to the rickettsiae and psittacosis-lymphogranuloma groups is controversial. Although, like viruses, all pathogenic forms of these organisms are obligate intracellular parasites, in other respects they resemble bacteria. Since a cell wall, deriving its rigidity from mucopeptide, which contains the amino sugar muramic acid as a key constituent, has so far only been found in bacteria and the closely related blue-green algae, the presence of muramic acid in an organism may be used as a taxonomic criterion. The mucopeptides of bacterial cell walls are also often sensitive to lysozyme, so that dissolution by this enzyme serves as an indication of the presence of mucopeptide. Organisms of the rickettsiae and psittacosis-lymphogranuloma groups have been examined for the presence of muramic acid. Critical chemical tests have shown that this substance is present in organisms of both groups. Cell walls of were dissolved by lysozyme. In the light of these and other results the taxonomic position of these groups of organisms is discussed.


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