PRODUCTION OF ANTIBIOTICS 



35 



clinical medicine must tak(> into considera- 

 tion the phenomena of absorption and 

 distribution in different body fluids (I^rics- 

 son, 19(i0). 



Increasing Commercial Yields 



For the chemical characterization of an 

 antibiotic, broths of low titer of activity 

 may be satisfactory. Howe\'er, for its com- 

 mercial production, broths of the highest 

 possible titers are desired. Yields can be in- 

 ci'eased by two general approaches, which 

 are usually utilized together. One can either 

 (1) improve the strain forming the antibiotic 

 by selection of more and more active mu- 

 tants, or (2) improve the media and cultural 

 conditions used for the growth of the anti- 

 biotic-producing organism. 



Strain Selection 



The ability of different strains of the same 

 organism to form different concentrations of 

 the same antibiotic is illustrated in Table 1 1. 



At least four distinct procedures are 

 utilized for obtaining more active strains 

 capable of producing higher concentrations 

 of a particular antibiotic: 



1. Selections from a natural population 

 of a culture and evaluation of antibiotic 

 potency of different strains of the particular 

 culture. 



2. Selection of strains from a given culture 

 grown on a medium enriched with the anti- 

 l)iotic produced l)y the particular culture. 



;'). Preliminary treatment of a culture 

 with ultraviolet and other radiations. 



4. Treatment of a culture with various 

 chemicals, such as ethylene amine, nitrogen 

 mustard, or colchicine. 



Natural selection is accomplished by plat- 

 ing out actmomycetes so as to get a large 

 number of isolated colonies, each one origi- 

 nating, if possible, from a single spore or 

 from small segments of mycelium. The level 

 of antibiotic production of these substrains 



Table 11 

 Antibiotic potency of different strains of S. fradiae, 

 (/roup I (Waksman et al., 1958) 

 Medium: N-Z-amine-glucose. Potency ex- 

 pressed in neomycin units per ml of broth. 



can be tested in a numbei' of ways. The sul)- 

 strains can be tested directly in lic[uid or in 

 solid media. In this case replication methods 

 are often used as a time-sa^'ing device, but 

 in final analysis an increase in antil^iotic 

 formation in lic[uid media is the aim. 



Actinomycetes, as a rule, are sensitive to 

 strictly antibacterial antibiotics and resist- 

 ant to strictly antifungal antil)iotics. These 

 properties can be utilized to isolate strains of 

 actinomycetes which pi-oduce antibacterial 

 antibiotics of a given type. Active strains 

 will be more resistant to the action of the 

 antibacterial antibiotics they produce than 

 will other actinomycetes, and the more 

 antibiotic a given strain will accumulate, the 

 more resistant the sti'ain will be. That this 

 phenomenon is not universal, however, is 

 evident from the fact that strains of Strepto- 

 myces rimosus forming oxytetracycline ai-e 

 resistant to streptomycin. 



Waksman et al. (194()) first suggested the 

 use of a streptomycin-enriched medium for 

 the selection of streptomycin-producing 

 cultures. Although the inactive variants were 

 thus eliminated, more active cultures were 

 not obtained. This method was later utilized 

 by AIcDani(4 and Hodges (1950) with con- 

 siderable success and resulted in the produc- 



