Chapter II — 37 — Important Types 



Litmus milk: Cream-colored ring; coagulated with rapid peptonization, be- 

 coming alkaline. 



Potato: Yellowish, wrinkled. 



Nitrites produced from nitrates. 



Proteolytic action in milk and gelatin. 



The pigment formed is not soluble. 



Starch is hydrolyzed. 



Aerobic. 



Optimum temperature 37°C. The optimum temperature for certain physio- 

 logical reactions is much lower; for example, 25° to 28° for streptomycin produc- 

 tion. 



Habitat: Peat, soils, river flats, and dust. Numerous strains of this organism 

 have been isolated from habitats which range from the throat of a chicken to that 

 of rich garden soils and cultivated peats. 



S. griseus represents a most variable group of organisms. This is 

 brought out quite emphatically in an examination of the ability of dif- 

 ferent strains within this species for their ability to produce antibiotic 

 substances. These have been classified into 4 groups. 



1. Those strains which produce streptomycin, the amount of antibiotic pro- 

 duced varying greatly with the individual strains under different conditions of 

 culture; they are sensitive to actinophage. 



2. Those strains which produce only or predominantly grisein or grisein-like 

 substances; they are resistant to actinophage. 



3. Those strains which produce other antibiotics, which are active against 

 gram-positive bacteria only, and the exact nature of which is still unknown. 



4. Those strains which produce no antibiotic at all. 



Another very important characteristic of S. griseus strains is their 

 ability to produce mutants. So far, 2 mutants have been isolated from 

 the streptomycin-producing cultures: (a). A colorless mutant, producing 

 no aerial mvcelium, not producing any streptomycin and sensitive to this 

 antibiotic as brought out in Table 4. (Z?). A pigmented mutant, pro- 

 ducing pink to vinaceous colored vegetative growth, but forming the 



Table 4: Streptomycin production and streptotnycin sensitivity of different strains of S. griseus 

 and their variants (395) : — 



Production of Streptomycin 

 Strain or variant Origin streptomycin* sensitivity** 



• Units of streptomycin in 12-day cultures. 

 •* Units of streptomycin required to inhibit growth of particular strain or variant in 1 ml of medii 



