MOKI'IIOI.OCN. ( ^TOLOC^'. AM) I,ll'i: ('V("M:s 



87 



A stroptomycos may lose, hy luiiiarKni or 

 l)y natural variation, the properly of toim- 

 inji; aerial niyccliiini; it may thus apjx'ai' to 

 li'row as a typical nocardia. This was found 

 1o hold true, foi' example, of the strepto- 

 luyciu-produciuji strain of N. (irisciis. When 

 this occurs, it is accompanied by a change 

 in the pliysiology of the organism, hut not 

 in the morphologictd properties of the \-ege- 

 tative growth. Freciuently such a cultui'e 

 may revert to its original form and i)r()duce 

 typical a(M-ial mycelium. 



To retain the property of proper sporula- 

 tion, cultures are usually maintained in soil. 

 A good soil with a fair supply of organic 

 matter, neutral or slightly alkaline in reac- 

 tion, with a moisture content of about GO 

 p(>r cent of the water-holding capacity so as 

 to favor proper aeration is inoculated with a 

 spore suspension or with substrate mycelium. 

 The flask is incubated at optimum tempera- 

 ture vmtil good growth is obtained. The flask 

 is then thoroughly shaken and further incu- 

 bated. After growth has reached a maxi- 

 nuun, the soil is allowed to desiccate. When 

 the culture is then transferred from the soil 

 to a synthetic agar medium, good sporula- 

 tion is obtained. Excess organic nitrogenous 

 nutrients, especially phospholipids, favor 

 substrate growth at the expense of the aerial 

 mycelium, as shown by Erikson (1947). 



Morphological Characteristics of Some 

 of the Important Genera of Actino- 

 mycetes 



Actinumijces 



The anaerobic pathogenic organisms l)e- 

 longing to the genus Actinomyces are gram- 

 positive, nonacid-fast, producing a branch- 

 ing vegetative mycelium. Xonsporing aerial 

 hyphae are occasionally formed in the firm- 

 textured .4. israeli. A. hovis, however, pro- 

 duces soft, smooth colonies, without aerial 

 mycelium. The vegetative mycelium divides 

 into diphtheroid rods (Erikson, 104!)). Club 



formations in tissues of the host, which at- 

 tracted so much attention among earlier 

 workers and which were also found (Wright 

 Naeshnid) in sennn or ascitic fluid media, 

 are now recognized to be mechanisms of 

 I'esistance of the host against invasion. 



According to Erikson (1953), the com- 

 bined demands of anaerobiosis, para.sitism, 

 and complex luitritive re(|uirements ap- 

 parently leave little scope for mycelial varia- 

 tion among the members of the genus Ac- 

 linomt/ces. These organisms exhibit a pattern 

 of (hn-elopnuMit similar to that of the no- 

 cardias, and the chief type of variation re- 

 ported is that of "smooth" and "rough" 

 colonies. The former is associated with 

 readily fragmented growths producing tur- 

 bidity in li(iuid cultures; the latter with co- 

 herent, filamentous, well-branched growths 

 leaving the liciuid substrate clear in the 

 manner characteristic of actinomycetes in 

 general. The changes described are from the 

 typical, rough, breadcrumb colony to the 

 soft smooth one, not the reverse (Triuss and 

 Politowa, H«l; Lentze, 1938; Ludwig and 

 Sullivan, 1952). 



According to Morris, .4. bovis passes 

 through a complete life cycle, consisting of 

 two clearly defined generations. The germi- 

 nation of the spores takes place bj- budding. 

 The mycelium, if formed, is less stable than 

 in the case of streptomyces. Branching is 

 impermanent in the haploid phase, but is 

 permanent in the diploid phase. The mech- 

 anism for the formation of the initial cell in 

 the genus Aciinomijccs is less specialized 

 than in the genus Streptomyces. A haploid 

 generation gives rise to a diploid generation 

 by conjugation of. two specialized haploid 

 cells. The diploid generation produces a 

 haploid spore by reduction division. The 

 club shape of the newly germinated diploid 

 form and the altered shape of the haploid 

 phase cells represent the pleomorphic forms 

 described by various investigators in cer- 



