DEHYDRATED CULTURE MEDIA 



59 



prevent the medium from settling out and burning on the bottom of the flask. 

 In the preparation of large quantities of medium (500 ml. or more) about three- 

 fourths of the water may be heated to boiling. The dehydrated medium is evenly 

 suspended in the remaining unheated distilled water, and this suspension is 

 promptly added to the boiling distilled water. The medium should be boiled for 

 several minutes to effect complete solution. 



Not all samples of fresh skim milk are satisfactory for the preparation of the 

 medium. For that reason we recommend the addition of 10 ml. of a 10 per cent 

 solution of Bacto-Skim Milk per liter of Tryptone Glucose Extract Agar after 

 the medium is in complete solution. 



The use of Pyrex or other hard glass containers is recommended for steriliza- 

 tion. 



Do not overheat medium in the autoclave. Care should be taken that the 

 autoclave reaches 15 pounds pressure (121°C.) promptly and be maintained 

 there for 15 minutes after which the steam supply is cut off and the autoclave 

 allowed to come to atmospheric pressure without unnecessary delay. Not more 

 than thirty to forty minutes for the complete operation should be required. The 

 medium should not be allowed to cool or solidify in the autoclave, but should be 

 removed promptly after sterilization. 



Do not hold melted agar at 45 °G. for over 30 minutes. Tryptone Glucose 

 Extract Milk Agar will flocculate if held at 43 to 45 °G. for longer than 30 min- 

 utes. This flocculation can be dispersed by re-heating the medium. The fioccula- 

 tion will not develop if the medium is held at 48 to 50°G. 



If it is not practical to follow the above directions in detail, and a troublesome 

 precipitate persists, the complete medium may be prepared by the addition of 

 sterile skim milk to sterile liquid Tryptone Glucose Extract Agar under aseptic 

 conditions, just prior to pouring plates. 



One pound of Bacto-Tryptone Glucose Extract Agar will make 18.9 liters of 

 medium. 



1 Standau-d Methods for the Examination 



of Dairy Products, gth Edition: 93: 1948. 

 3 Methods and Standards for the Production 



of Certified Milk. 21:1950. 

 8 Standard Methods for the Examination 



of Water and Sewage, gth Edition: 191 : 1946. 

 * Tech. BuU. 228. N. Y. State Agr. 



Exp. Sta., 1935. 

 6 Am. J. Pub. Healtk, 28:148:1938. 

 « Proc. 36th Cong. Intern. Assoc. Ice 



Cream Manufacturers, 2:132:1936. 

 'J, Dairy Science, 20:445:1937. 



8 Tech. BuU. 147, N. Y. State Agr. 



Exp. Sta., 1928. 

 8 Standard Methods of Milk Analysis, 



6th Edition: 60: 1934. 

 ^ Standard Methods for the Examination 



of Dairy Products, gth Edition: 343: 1948. 

 ^ J. Dairy Science, 18:647:1935. 

 "Am. J. Pub. Health, 28:1447:1938. 

 ^ Ninth Annual Year Book (ig38-39) p. 79, 



Suppl., Am. J. Pub. Health, 29:No. 2:1939. 

 i*Am. J. Pub. Health, 29:821:1939. 



BACTO 



BRILLIANT GREEN BILE 2% 



DEHYDRATED 



A complete discussion of this medium as used in the presumptive test for coli- 

 form organisms in milk and other dairy products is given under Bacto-Brilliant 

 Green Bile 2%, page 37. This medium has also been referred to as Brilliant 

 Green Lactose Peptone Bile, and similar variations. 



