DEHYDRATED CULTURE MEDIA 207 



potent penicillin preparations can be assayed with fewer dilutions than in the 

 serial dilution technique. 



More recently the Food and Drug Administration^ recommended modifica- 

 tions of this medium for use in the cylinder plate method. Bacto-Penassay Base 

 Agar and Bacto-Penassay Seed Agar used in this procedure are discussed on 

 pages 204 and 205. 



Plates are prepared the day previous to the actual testing of penicillin samples 

 by adding 22 ml. of Yeast Beef Agar to petri dishes (100 x 20 mm.) which then 

 stand at room temperature for 24 hours before being overlaid with 3 ml. of Yeast 

 Beef Agar previously inoculated with the test organism, Micrococcus pyogenes 

 var. aureus (P209). 



To rehydrate the medium, suspend 26.5 grams of Bacto-Yeast Beef 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 6.6. 



One pound of Bacto-Yeast Beef Agar will make 17.5 liters of medium. 



1 J. Bact., 47:199:1944. Assay for Antibiotic Drugs, Federal Security 



2 Lancet, 2:177:1941. Agency, Food and Drug Adininistration. 

 * The Compilation of Tests and Methods of 



BACTO 



MYCIN ASSAY BROTH (B295) 



DEHYDRATED 



Bacto-Beef Extract 5 g. 



Bacto-Peptone 10 g. 



Sodium Chloride 2.5 g. 



Bacto-Mycin Assay Broth duplicates the formula of the medium recommended 

 by Price, Nielsen and Welch^ for their serial dilution method of assay of strepto- 

 mycin in body fluids. 



The authors found that the turbidimetric method in use for assaying strepto- 

 mycin in aqueous or buffered solution gave erroneous results when used for 

 testing body fluids because of the stimulating properties of these fluids for the 

 test organism. Also, that the equipment and material required for the agar 

 cylinder plate method may not be readily available to the small laboratory. For 

 these reasons a study was made to determine which organism would lend itself 

 to use in a simple serial dilution procedure for determining streptomycin in body 

 fluids. They found that Bacillus circulans was the most sensitive to streptomycin 

 and gave reproducible results. 



Essentially, the test consists in preparing various dilutions of the fluid under 

 test in sterile Bacto-Mycin Assay Broth. A streptomycin of known potency is used 

 as a standard and is serially diluted in a similar manner. The tubes are inoculated 

 with the test organism and incubated at 37°C. over night. The concentration of 

 streptomycin in the unknown is determined by comparing the end point in the 

 unknown with that in the standard. 



To rehydrate the medium, dissolve 17.5 grams of Bacto-Mycin Assay Broth in 

 1000 ml. cold distilled water. Distribute in tubes and sterilize in the autoclave 

 for 15 minutes at 15 pounds pressure (121°G.). The final reaction of the medium 

 will be pH 7.9. 



One pound of Bacto-Mycin Assay Broth will make 25.9 liters of medium. 



1 Science, 1 03 : 56 : 1 946. 



