ISOLATION, IDliN rU'lCAIloN, ( l i;i"I\ A TloN , AND I'ln :S1 ;H\ A'llON 



Zi) 



break up into small particles and are in()i(> 

 resistant to shakiii.i;; than are \-eu;etat i\-e iVaii;- 

 nients. W'i^etat i\'e niyceliuin may llnis be 

 (listin.uuisluHl from spores 1)V the manner in 

 which the xiahle count \ai'ies with time ot 

 shakinii;. Althou<!;h it was not possible to es- 

 timate the numhiMs of spoi-(\s and of \-ej;-eta- 

 tix'e particles in mixed suspension, cei'tain 

 pre(lominatin,u" forms could he identilied. 



Selective (".iillure .Methcxls 



'I'he select i\{> culture methods for the iso- 

 lation of actinomvcetes are based on the use 

 of media that contain specific nutricMits fa- 

 x'orable tor select i\'e de\(>lopment of the or- 

 j^anisms. Such media may contain nutrients 

 favorable to actinomvcetes, because of tluMr 

 specific metabolism, such as paraffin utiliza- 

 tion, steroid oxidation, or keratin decompo- 

 sition. On the other hand, substances are 

 added to the medium which may discourage 

 the growth of fungi and bacteria. With the 

 growing appreciation of the l)iochemical po- 

 tentialities of various actinomycetes, espe- 

 cially as regards formation of antibiotics, vi- 

 tamins, and enzjanes, the development of 

 special media for the enumeration and iso- 

 lation of particular organisms has great pos- 

 sibilities. 



'^I'he incorporation of antibiotics and other 

 antimicrobial substances in such media offers 

 some very interesting potentialities. On the 

 one hand, certain antibiotics may be used 

 to repress l)acteria or fungi and allow only 

 particular actinomycetes to develop. On the 

 other hand, antibiotics may be employed for 

 the selection of ^•igorous strains of organisms 

 capable of producing these antibiotics. 



For the purpose of suppressing fungi, 

 C'orke and Chase suggested the use, in plat- 

 ing media for actinomycetes, of cyclohe.xi- 

 mide (40 Mg/'iil of medium added just prior 

 to the pouring of the plates). The presence^ 

 of the antibiotic not only results in the I'e- 

 l)ression of the fungi, but also gi\'es nnich 

 laigei' numbers of actinomycetes. This pro- 



Fua HK 1(). Typicul zonation in the aerial my- 

 feliuin 1)1' a st reptomyce.s colony (Reproduced 

 from: Lie.ske, R. Morphologic vnd Biologie der 

 Strahlenpilze. Verlag von Gebriider Borntraeger, 

 Loil)zig, 1921, ]). 168). 



T.\BLE 3 



EjD'cct of shaking upon suspensions of substrate 

 actinomycete mycelium (Skinner) 



* Vegetative culture diluted in saline; mean of 

 three replicate plates reported. 



cedure was found to be superior to the use 

 of sodium propionate, mentioned previously 

 (Crook ct al.). The incorporation of nitro- 

 furazone or other antibacterial agents will 

 also favor the development of actinomycetes 

 on tlie plate, as shown by Yoshioka. Unfor- 

 tunately, no antibiotic or other antimicrobial 

 substance has yet been found that would 

 inhibit selecti\-ely the separate genera of 

 actinomycetes. 



The addition of antibiotics to media for 

 the purpose of enriching specific antibiotic 



