212 DIFCO MANUAL 



MEDIA FOR THE ASSAY 

 OF VITAMINS AND AMINO ACIDS 



The Difco dehydrated media described in this section are prepared especially 

 for use in the microbiological assay of vitamins and amino acids. Two types of 

 media are employed for this purpose, one for carrying the culture in stock or 

 preparing the inoculum, the other for assay. The latter type of media contain all 

 the factors necessary for growth of the test organism except one essential 

 ingredient. 



Each medium for assay purposes is free from the essential growth requirement 

 factor for which the medium is recommended. When this factor is added, in 

 specified increasing concentrations, the growth response of the particular test 

 organism is measured either acidimetrically or turbidimetrically. In the per- 

 formance of the various tests the basal medium is prepared and is generally 

 tubed in 5 ml. amounts. To one series of tubes are added graded quantities of 

 the known essential ingredient. To the second similar series are added varying 

 amounts of the material under investigation. Included in each series of tubes is 

 one containing only distilled water and the basal medium. This tube acts as a 

 blank control. The tubes of each series are then made up to 10 ml. with distilled 

 water. 



Great care to avoid contamination of media or glassware must be taken in 

 microbiological assay procedures. Extremely small amounts of foreign material 

 may be sufficient to give erroneous results. Scrupulously clean glassware free from 

 detergents and other chemicals must be used. For example, in the assay of 

 Vitamin B12, as small a quantity as 0.01 millimicrogram will give rise to a 

 definite growth response. The importance of clean glassware in the assay of this 

 vitamin was stressed by the U. S. Pharmacopeia Vitamin Bjg Study Panel, since 

 they stated that glassware for this purpose required special handling, and as 

 many as twelve rinses appeared to be necessary for satisfactory results. 



For the successful execution of these procedures all conditions of the assay 

 must be adhered to meticulously. In the description of each medium points of 

 prime importance for successful assays have been stressed. 



BACTO 



MICRO ASSAY CULTURE AGAR (B319) 



DEHYDRATED 



Bacto-Yeast Extract 20 g. 



Proteose Peptone No. 3, Difco 5 g. 



Bacto-Dextrose 10 g. 



Monopotassium Phosphate 2 g. 



Sorbitan Monooleate Complex 0.1 g. 



Bacto-Agar 10 g. 



Bacto-Micro Assay Culture Agar is recommended for carrying stock cultures of 

 Lactobacilli and other test organisms used for microbiological assay. This medium 

 is also recommended for the general cultivation of Lactobacilli and many other 

 microorganisms. 



In the microbiological assay of vitamins and other essential nutriments, the 



