92 



NATURE, FORMATION, AND ACTIVITIES 



mous size and assuming most peculiar forms ; 

 spore formation is repressed; delayed non- 

 spore-forming variants are produced with a 

 modified type of growth on nutrient media. 

 The cells of bacteria subject to the action of 

 streptothricin are greatly enlarged as a re- 

 sult of incomplete fission. 



Action of Specific Antibiotics 



Streptomycin 

 The mode of action of streptomycin upon 

 bacteria has received much consideration. 



Some of the observations appear to be 

 unrelated. Macheboeuf (1948) reported inhi- 

 bition by the antibiotics of dephosphoryla- 

 tion of mononucleotides and depolymeriza- 

 tion of nucleic acids. Wight and Burk (1951) 

 reported inhibition of oxygen consumption 

 of resting cells of E. coli on various substrates 

 and an inhibitory effect of dihydrostrepto- 

 mycin upon pyruvate fermentation by E. 

 coli (Fig. 4). On the other hand, stimulation 

 by streptomycin of oxygen consumption of 

 E. coli with some of the same substrates has 



200 



TIME-HOURS 



Figure 4. Effect of streptomycin on the oxygen consumption involving oxalacetic acid and pyruvic 

 acid. (Reproduced from Wight, K. and Burk, D. Antibiotics & Chemotherapy 1: 380-38G, 1951.) 



