22 



THE ACTINOMYCETES, Vol. II 



Work (1957) have shown that these genera 

 can be differentiated by the configuration of 

 the diaminopimelic acid present in whole cell 

 hydrolysates; streptomycete cell Avails con- 

 tain the L-isomer, whereas nocardiae cell 

 walls contain the DL-isomer. Cummins and 

 Harris (1958) reported that the presence or 

 absence of arabinose in the hydrolysates of 

 the intact organisms can also be used to 

 identify them; nocardiae cell walls contain 

 arabinose, whereas streptomycete cell walls 

 do not. The sensitivity of most Stnptomyces 

 species, but not of nocardiae, to the action of 

 lysozyme on their cell wall preparations, 

 studied by Sohler, Romano, and Nickerson 

 (Volume I, p. 159), provides further criteria 

 for distinguishing between members of these 

 two genera. Studies of infrared absorption as 

 a taxonomic criterion (Riddle et al., 1956) 

 has also been suggested.* 



In view of the overlapping between certain 

 forms placed for convenience in either one 

 genus <)]• the other, the separation of atypical 

 strains of Nocardia or Streptomyces by mor- 

 phology or fermentation tests alone may be 

 difficult, as pointed out by Gordon and 

 Mihm (1957). 



The genus Nocardia has been described in 

 the last edition of Bergey's Manual as 

 follows: 



"Slender filaments or rods, frequently 

 swollen and occasionally branched, forming 

 a mycelium which, after reaching a certain 

 size, assumes the appearance of bacterium- 

 like growths. Shorter rods and coccoid forms 

 are found in older cultures. Conidia not 

 formed. Stain readily, occasionally showing a 

 sligh.1 degree of acid-fastness. Xonmotile.t 



* Personal communication from Dr. X. M. 

 McClung. 



t The existence of motility among the nocardias 

 was considered by Jensen (1953) as indisputable, 

 and this really is not surprising in view of the 

 numerous observations on motility in the closely 

 related coryneform bacteria. The species in the 

 order Actinomycetales cannot any longer be re- 

 garded a,< constantly nonmotile (Fig. 14). 



Xo endospores. Aerobic. Gram-positive. The 

 colonies are similar in gross appearance to 

 those of the genus Mycobacterium. Paraffin. 

 phenol and m-cresol are frequently utilized 

 as a source of energy. 



"In their early stages of growth on culture 

 media (liquid or solid), the structure of 

 nocardias is similar to that of actinomycetes 

 in that they form a typical mycelium; hy- 

 phae branch abundantly, the branching 

 being true. The diameters of the hyphae vary 

 between 0.5 and 1 /x, usually 0.7 to 0.8 jx, 

 according to the species. The mycelium is 

 not septate. However, the further develop- 

 ment of nocardias differs sharply from that 

 of actinomycetes; the filaments soon form 

 transverse walls and the whole mycelium 

 breaks up into regularly cylindrical short 

 cells, then into coccoid cells. On fresh culture 

 media, the coccoid cells germinate into my- 

 celia. The whole cycle in the development of 

 nocardias continues for 2 to 7 days. Most 

 frequently the coccoid cells are formed on 

 the third to fifth day, but in certain species 

 they can be found on the second day. 



"The multiplication of nocardias proceeds 

 by lission and budding; occasionally they 

 form special spores. Budding occurs often. 

 The buds are formed on the lateral surface 

 of the cells; when they have reached a cer- 

 tain size, they fall off and develop into rod- 

 shaped cells or filaments. The spores are 

 formed by the breaking up of the cell plasm 

 into separate portions usually forming 3 to 

 5 spores; every portion becomes rounded, 

 covered with a membrane and is t ransformed 

 into a spore; the membrane of the mother 

 cell dissolves and disappears. The spores 

 germinate in the same way as those of ac- 

 tinomyces. They form germ tubes which 

 develop into a mycelium (Fig. 7). 



"The colonies of nocardias often have a 

 paste-like or mealy consistency and can 

 easily be taken up with a platinum loop; they 

 spread on glass and occasionally render the 

 broth turbid. The surface colonies are 



