MODES OF ACTION OF ANTIBIOTICS 



103 



radation product, forms a substitute for 

 streptomycin. (4) A group similar in proper- 

 ties to the first, but showing restricted 

 growth on appropriate mixtures of catenuhn 

 and streptidine or streptobiosamine; it pro- 

 duced frequent mutants which belonged to 

 the second class. Other substances related to 

 streptomycin or neomycin were either inac- 

 tive (streptamine, streptiu'ea, methylneo- 

 biosaminide) or inhibitor}^ (neomycin B and 

 C, kanamycin, streptidine) to all the classes 

 of streptomycin-dependent mutants. Strep- 

 tomycin and catenulin, when present alone 

 in concentrations of 5 to 100 yug per ml, gave 

 good growth of the second and third classes 

 of dependent mutants. A mixture of the two 

 antibiotics, however, in any proportion so 

 long as the concentrations surpassed 2 /ug per 

 ml, prevented growth of the organisms. The 

 dependent cells grown in the presence of one 

 antibiotic behaved as sensitive cells in 

 respect to the other, indicating diverse 

 mechanisms of growth-promoting action for 

 streptomycin and catenulin. Xeamine ex- 

 hibited similar nutritional incompatibility 

 with various streptomycins. 



Hashimoto (1955) obtained a partially 

 streptomycin-dependent strain from the 



parent strain of pneumococcus I by succes- 

 sive cultivation in media containing increas- 

 ing amounts of streptomycin. This strain 

 gave the same amount of bacterial growth on 

 media containing no streptomycin and on 

 media with 1 mg per ml of streptomycin, 

 but the growth was faster in the latter. 

 Crude deoxynucleic acid prepared from the 

 partially streptomycin-dependent strain 

 could bring about transformation of the 

 streptomycin-indifferent strain in similar 

 ratio. The deoxynucleic acid was believed 

 to have a factor that controlled the depend- 

 ence on 50 to 100 /xg of streptomycin and 

 that was imparted to the streptomycin- 

 sensitive strains. 



Streptomycin-dependent cultures also 

 show back mutations. Yegian and Budd 

 (1951) obtained from such strains of Myco- 

 hacteriirm ranae either parent sensitive cul- 

 tures or streptomycin-resistant variants, 

 with no discernible change in colony mor- 

 phology. 



Thind (1958) reported that extracts of 

 certain streptomycin-sensitive cultures of E. 

 coll produce a substance which can replace 

 streptomycin in supporting the growth of 

 streptomycin-dependent organisms. 



