PRODUCTION OF ANTIBIOTICS 



33 



Protluclion of DifTerent Antibiotics by 

 the Same Organism 



Not only may the antibiotic produced by 

 an organism vary in chemical composition, 

 but its very nature may differ (Trussel ct al., 

 1947). This can easily be demonstrated by 

 the fact that freciuently the same organism 

 may produce both antibacterial and anti- 

 t'lmgal antibiotics. Thus, S. griseus was 

 found to produce streptomycin, candicidin, 

 and cycloheximide; S. Jradiac produces 

 neomycin and fradicin; S. rimosus forms 

 oxy tetracycline and rimocidin. Frecjuently, 

 different strains of the same organism pro- 

 duce different antibiotics. This is true, for 

 example, of different strains of S. lavcndidac, 

 which produce several forms of strepto- 

 thricin and also a \'ariety of such compounds 

 as ehrlichin and polyenes. Often a change in 

 composition of medium and in conditions of 

 growth results in a change in the nature of 

 the antibiotics produced by the same organ- 

 ism. Certain organisms are capable of form- 

 ing in the same medium as many as three 

 different antibiotics (Despois et al., lOotJ). 

 S. alhirHiculi, for example, produces euro- 

 cidin, enteromycin, and cai'bomycin (Osato 

 etal, 1955). 



Production of Antibiotics in Li<{uid and 

 Solid Media 



As was shown in Chapter 3, the fact that 

 an actinomycete has antagonistic properties 

 sometimes may not be discovered until after 

 it has been grown both on solid media and 

 in licjuid media. For instance, the culture 

 may form zones of inhiliition agahist test 

 organisms on solid media, but may refuse 

 stubbornly to produce antibiotics in li(iuid 

 media. This may l)e due to differences be- 

 tween the cultural conditions of some actino- 

 mycetes on the two different types of media. 

 In certain cases, for example, this phenome- 

 non can be explained by the formation of 

 ammonia by the actinomycete. It can easily 

 be demonstrated that some actinomycetes 



can produce a volatile substance which is 

 toxic to fungi. Inhilntion of the fungi can be 

 noted not only on the layer of agar on which 

 the organism is growing, but also on a layer 

 that is on top of it and separated by an air 

 space. The pH of this upper layer of agar 

 increases during the growth of the actino- 

 mycete on the layer below, and fungi seeded 

 on this upper layer will not grow, whereas 

 some bacteria will. Substitution of a dilute 

 solution of ammonia for the growing actino- 

 mycete produces a similar inhibitory effect 

 on fimgi. These experiments do not rule out 

 the possibility that actinomycetes form 

 \'olatile antibiotics different from ammonia, 

 but the production of this compound can 

 probably explain certain discrepancies be- 

 tween inhibitory effects observed when 

 actinomycetes are grown on solid and in 

 li(iui(l media. 



In general, once an antagonistic actino- 

 mycete has been selected in a screening 

 pi'ogram, the antibiotic or antibiotics pro- 

 duced tjy this organism must l)e obtained in 

 large enough (juantities to permit their 

 exti'action, purification, characterization, 

 and if necessary, the study of their toxicity, 

 pharmacology, and activity in vivo. This is 

 accomplished by growing the antagonist in 

 liciuid cultures which are incubated on shak- 

 ing machines or in fermentors of various 

 volumes. 



The motion applied to flasks by shaking 

 machines is either circular (rotary shakers) 

 or linear (reciprocal shakers). The purpose 

 of the shaking is to furnish the culture with 

 the aeration necessary for maximal growth 

 and the formation of antiV)iotics. The mo- 

 tion may also play a role in keeping the 

 organism well dispersed in the liciuid me- 

 dium, permitting good contact between the 

 cell surfaces and the nutrients. 



Assay Methods 



Since antibiotics are chemical substances 

 capable of inhibiting the growth of micro- 



