DEHYDRATED CULTURE MEDIA 75 



Bacto-Skim Milk may be used in media for the detection of proteolyzers, and 

 as an ingredient in the preparation of media for the cultivation of such organisms 

 as Mycobacterium tuberculosis and Corynebacterium diphtheria. A solution of 

 Bacto-Skim Milk containing litmus is a widely used medium for determining 

 acid production in milk and also the ability to peptonize or coagulate milk in 

 the identification of microorganisms. Skim Milk is used to detect the so-called 

 "stormy fermentation" of Clostridium perfringens. 



Nungester and Ellingson^ have suggested the addition of 0.1 per cent agar and 

 iron, either in the form of filings or freshly pickled strips, to adjust the oxygen 

 tension of the medium and permit more rapid development of organisms in the 

 "stormy fermentation" test. 



To rehydrate Bacto-Skim Milk to obtain the equivalent of fresh skim milk, 

 dissolve 100 grams in 1000 ml. of cold distilled water. Distribute in tubes and 

 sterilize in the autoclave for 15 minutes at 15 pounds pressure (121°G.). Over- 

 heating during sterilization results in the carmelization of the milk sugar. This is 

 to be avoided since the resulting discoloration may give an atypical appearance 

 of the sterile medium and may be further reflected in the appearance of growing 

 cultures. The final reaction will be pH 6.4. 



One pound of Bacto-Skim Milk will make 4.5 liters of skim milk. 



^ Standard Methods for the Examination ' Personal Communication, 



of Dairy Products, 9th Edition: 93: 1948. 



BACTO 



PEPTONIZED MILK (B35) 



DEHYDRATED 



Bacto-Peptonized Milk is used alone or as an ingredient in media for isolatioa 

 and cultivation of the Lactobacilli and organisms encountered in the bacterio- 

 logical examination of milk and dairy products. 



As early as 1894 Kayser^ used Peptonized Milk in his studies on lactic fermen- 

 tation. Orla-Jensen^ found Peptonized Milk to be exceptionally satisfactory in 

 the cultivation of lactic acid forming organisms. Bacto-peptonized Milk was 

 developed in our laboratories to provide a simple medium with readily available 

 nitrogen for the cultivation of organisms of the Lactobacillus group. It contains 

 the degradation products of the proteins, albumins, and globulins of milk, and 

 therefore its nitrogen is more readily available for bacterial assimilation than 

 the native proteins of milk. Rapid and luxuriant growth of Lactobacilli is readily 

 obtained in solutions of Bacto-Peptonized Milk. For carrying stock cultures of 

 lactic organisms, it is recommended that 0.1 per cent of Bacto-Agar be added 

 to the medium. Kulp and White^ used Bacto-Peptonized Milk with excellent 

 results in their Tomato Juice Agar for Lactobacillus acidophilus. Devereux* 

 employed Bacto-Peptonized Milk in his modification of the Cooledge Medium 

 for testing the quality of milk. Weiss and Rettger^ used Bacto-Peptonized Milk 

 in their tomato juice media for L. bifidus. 



To rehydrate the medium, dissolve 15 grams of Bacto-Peptonized Milk in 

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

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

 medium will be pH 6.5. 



One pound of Bacto-Peptonized Milk will make 30.2 liters of medium. 



^Ann. inst. Pasteur, 8:737:1894. * Am. J. Pub. Health, 22:1291:1932. 



aCentr. Bakt., H Abt., 4:96:1898. b j. fiact., 28:501:1934. 



8 Science, 76:17:1932. 



