24 



NATURE, FORMATION, AND ACTIVITIES 



gi'uiii-positive bacteria and mycobacteria 

 are inhibited by a larger percentage of 

 actinomycetes than are gram-negative bac- 

 teria. Fungi are also inhibited b}^ a large 

 number of actinomycetes. ^lany inhibitors 

 of phages can be detected in the culture 

 filtrates of actinomycetes, but their anti- 

 phage action does not show correlation with 

 true antiviral action. As has already been 

 mentioned, no useful anti\'iral antibiotic has 

 yet been discovered. 



Routien and Finlay (1952) screened 

 thousands of soil samples obtained from 

 widely scattered geographical areas. Certain 

 organisms producing streptomycin, strepto- 

 thricin, chloramphenicol, actinomycin, and 

 xanthomycin-like antil)iotics were extremely 

 common; in fact, they were of worldwide 

 distribution. Tetracycline-producing cul- 

 tures were isolated only a few times. One 

 antibiotic was obtained from only one 

 culture isolated from one particular soil. 

 Certain antibiotics were produced by or- 

 ganisms common in soils in certain localized 

 areas. Other antibiotics came from soils 

 collected within a restricted area. I'mezawa 

 et al. (1949), using the technique of Waks- 

 man and Schatz (194()) of adding a particu- 

 lar antibiotic (chloramphenicol) to the 

 medium before plating out soil samples, were 

 able to demonstrate the presence of a rather 

 large number of chloramphenicol-producing 

 strains, thus suggesting a wide distribution 

 of these organisms. 



Janot d al. (1954) isolated 7941 cultures 

 of Streptomyces; 351 of these produced anti- 

 biotics. Streptothricin-protlucers were most 

 common, followed by streptomycin-, then 

 tetracycline-producers. Various cultures ca- 

 pable of forming framycetin (neomycin) were 

 also fovmd, followed by a group of non- 

 identified antibiotics. 



Hirabayashi (1959) examined oKi cul- 

 tures of streptomycetes for antiamebic ac- 

 tivities. Nine of the cultures were found to 

 have direct antiamebic effects. An acti\'e 



substance was isolated from one culture of 

 Streptomyces and was named protomycin. It 

 had no antibacterial activities. Protomycin 

 showed inhibitory activity upon the growth 

 of Endamoeba histolytica at a concentration 

 of 25 /xg per ml after 24 hours of incubation 

 and at a concentration of 1 .(> ng per ml after 

 48 hours of incubation. Woodruff' and 

 AIcDaniel (1958) emphasized that, on the 

 a\'erage, 25 per cent of cultures of strepto- 

 mycetes isolated were able to produce some 

 kind of an antibiotic. About 90 per cent of 

 all the antil)iotic-producing cultures were 

 found to form streptothricin or closely re- 

 lated compounds. At least half of the re- 

 mainder produced streptomycin. Of the 

 others, one third formed tetracyclines, and 

 most of the rest could be identified with one 

 of the hundreds of antibiotics which have 

 been descril)ed from species of Streptomyces. 

 In a study of 10,000 cultures isolated, about 

 2,500 showed antibiotic activity. All but 250 

 gaA'e streptothricin-like antibiotics; about 

 125 formed streptomycin; 40 produced 

 tetracyclines; and 55 yielded other pre- 

 viously described antibiotics. Only 30 

 cultures seemed to form new antibiotics. 



The above calculations are based upon the 

 examination of antibacterial antibiotics. 

 Had a similar study included antifungal 

 agents as well, especially the polyene type 

 of compounds, the latter would have been 

 found to play an important part in the 

 distribution of antibiotic-producing prop- 

 erties among actinomycetes. Vanek and co- 

 workers (1958) found that 16.3 per cent of 

 739 freshly isolated strains of actinomycetes 

 produced polyenes. Heptaenes were the 

 most commonly produced polyenes, as re- 

 ported in 1956 by Pledger and Leche\-alier. 



Plotho (1947) tried to correlate pigment 

 production with antibiotic activity. A 

 collection of 291 cultures were classified into 

 four groups on the basis of pigments pro- 

 duced either in the mycelium or in the 

 m(Hlium. Of 61 cultures (21 per cent) show- 



