MoHriioT.ocs', ( '^ 'l'()l,(»(;^ , and Lii'-h; ('\t'les 



89 



FiGTRE 45. Helatioii.ships of the genus Nocardia to other genera of actinomycetes (Redrawn from: 

 Umbreit, W. W. and McCo.y, E]. Symp. on hydrobiologi/, p. 108, 1941). 



mycelium. Aerial hyphae may he formed, 

 but they are usually indistinguishable from 

 the substrate mycelium. The nonseptated 

 hyphae of both the substrate and aerial 

 mj^celium break up into short rods and 

 cocci, by the "segmentation" process, giving 

 rise to oidia-like spores. These germinate, 

 forming a true mycelium. Nocardias are 

 either acid-fast or nonacid-fast. Some no- 

 cardias are characterized by marked pleo- 

 morphism (Karwacki). The angular type of 

 growth described for some of the actino- 

 mycetes is also a property of some nocardias. 

 Erikson (1949) examined 300 strains of 

 nocardias, some freshl}^ isolated and some 

 ol)tained from culture collections. On im- 

 mediate isolation, only 9 per cent were 

 parti}' acid-fast, but on subseciuent culti\a- 

 tion on media rich in organic matter, such as 

 milk or nutrient broth, this percentage in- 



creased to 31. These nocardia cultures ranged 

 from soft mycobacterial tj^pe growth, with 

 transient \'egetative mycelium and very 

 sparse aerial mycelium, to the harder strep- 

 tomyces-like forms. No evidence was ob- 

 tained of any resting spores or chlamydo- 

 spores in the vegetative mycelium. The lack 

 of aerial spores, as well, led to the conclu- 

 sion that the nocardias should be regarded as 

 asporogenous. The phenomena of "cystites" 

 of Jensen (1932) and "involution forms" of 

 0rsko\' were l)eli(>\-ed to be vegetative in ori- 

 gin. 



0rsk()v dixided the nocardias into two 

 groups: Ila, with aerial mycelium, and lib, 

 without aerial mycelium. The first is asso- 

 ciated with a more stable, well-branched 

 vegetative mycelium approaching in struc- 

 ture that of the strcptomyces. The second 

 produces soft, mycobacterial, unstable my- 



