208 DIFCO MANUAL 



BACTO 



STREPTOMYCIN ASSAY AGAR (B277) 



DEHYDRATED 



Bacto-Beef Extract 1.5 g. 



Bacto- Yeast Extract 3 g. 



Bacto-Peptone 6 g. 



Bacto- Agar 15 g. 



Bacto-Streptomycin Assay Agar was originally developed with the coopera- 

 tion of Dr. Phillip S. Skell, University of Illinois, for the assay of streptothrycin. 

 Later, this medium was found to give excellent results for the streptomycin 

 assay, using the cylinder plate technique with Bacillus subtilis (ATCC ?$^6633) 

 as the test organism. The use of this medium assures well-defined zones of inhibi- 

 tion of growth of the test organism. 



Plates are prepared the same day samples are to be tested by adding 21 ml. 

 of Bacto-Streptomycin Assay Agar to petri dishes (100 x 20 mm.). After this base 

 layer has solidified, it is overlaid with 4 ml. of Streptomycin Assay Agar previ- 

 ously inoculated with spores of the test organism. 



To rehydrate the medium, suspend 25.5 grams Bacto-Streptomycin Assay Agar 

 in 1000 ml. cold distilled water and heat to boiling to dissolve the medium com- 

 pletely. Distribute in 500 ml. quantities in one-liter Erlenmeyer flasks. Sterilize in 

 the autoclave for 15 minutes at 15 pounds pressure (121°C.). The final reaction 

 of the medium will be pH 8.0. 



One pound of Bacto-Streptomycin Assay Agar will make 17.7 liters of medium. 



BACTO 



MYCIN ASSAY AGAR (B281) 



DEHYDRATED 



Bacto-Beef Extract 3 g. 



Bacto-Peptone 5 g, 



Bacto- Agar 15 g. 



Bacto-Mycin Assay Agar duplicates the formula of the medium specified by 

 the Food and Drug Administration^ for assay of streptomycin by the cylinder 

 plate method. The use of this medium assures well defined zones of inhibition of 

 the test organism. 



The general principles used for the assay of penicillin have proved practical 

 for the assay of streptomycin. However, different antibiotics require different test 

 organisms and a slight change in the composition of the medium employed. The 

 Food and Drug Administration has specified that the medium used in the assay 

 of streptomycin should have an alkaline reaction and that the test organism be 

 Bacillus subtilis (ATCC ?^6633). 



Plates are prepared the same day samples are to be tested by adding 21 ml. of 

 Mycin Assay Agar to petri dishes (100 x 20 mm.). After this base layer has solid- 

 ified it is overlaid with 4 ml. of Mycin Assay Agar previously inoculated with 

 spores of the test organism. 



To rehydrate the medium, suspend 23 grams of Bacto-Mycin Assay Agar in 

 1000 ml. cold distilled water and heat to boiling to dissolve the medium com- 

 pletely. Distribute in 500 ml. quantities in one-liter Erlenmeyer flasks. Sterilize in 



