DEHYDRATED CULTURE MEDIA 189 



tions of some of these carbohydrates, each ampul containing 10 ml. of a 10 per 

 cent solution, or 1 gram of the carbohydrate (see page 292). 



BACTO 



PHENOL RED CARBOHYDRATE AGARS 



DEHYDRATED 



Complete fermentation media, prepared with Bacto-Phenol Red Agar Base 

 and 1 per cent of the more frequently used carbohydrates, are also available. The 

 dehydrated media included in this group are: 



BACTO-PHENOL RED DEXTROSE AGAR (B99) 

 BACTO-PHENOL RED LACTOSE AGAR (BlOO) 

 BACTO-PHENOL RED MANNITOL AGAR (B103) 

 BACTO-PHENOL RED SACCHAROSE AGAR (BlOl) 

 BACTO-PHENOL RED MALTOSE AGAR (B102) 



To rehydrate the media, suspend 41 grams of the Bacto-Phenol Red Carbo- 

 hydrate Agar in 1000 ml. cold distilled water and heat to boiling to dissolve the 

 media completely. The complete media are sterilized, as described above, using 

 the minimum amount of heat necessary, for not more than 15 minutes at 15 

 pounds pressure (121°C.). The final reaction of these media will be pH 7.4. 



One pound of each complete Bacto-Phenol Red Carbohydrate Agar will make 

 12.6 liters of medium. 



BACTO 



PURPLE BROTH BASE (B227) 



DEHYDRATED 



Bacto-Beef Extract 1 g. 



Proteose Peptone No. 3, Difco . . 10 g. 



Sodium Chloride 5 g. 



Bacto-Brom Cresol Purple 0.015 g. 



Bacto-Purple Broth Base is recommended for the preparation of carbohydrate 

 broths used in fermentation studies for the cultural identification of pure cultures 

 of microorganisms, particularly members of the enteric group. We have prepared 

 Bacto-Purple Broth Base, containing the indicator brom cresol purple, and 

 adjusted to a final reaction of pH 6.8, for the convenience of bacteriologists desir- 

 ing carbohydrate differential broths of slightly acid reaction and containing a 

 sensitive sulfonephthalein indicator capable of demonstrating minute change in 

 reaction. It is free from fermentable carbohydrates which could give erroneous 

 results. 



The concentration of carbohydrate generally employed for testing the fer- 

 mentation reactions of bacteria is 0.5 or 1.0 per cent. Some investigators prefer 

 to use 1.0 per cent rather than 0.5 per cent to insure against reversion of the 

 reaction due to depletion of the carbohydrate by some microorganisms. Tubes of 

 Purple Lactose Broth and Purple Saccharose Broth should be tightly stoppered 

 during the incubation period for fermentation studies of the enteric group, to 

 avoid reversion of reaction. 



To rehydrate the medium, dissolve 16 grams of Bacto-Purple Broth Base in 

 1000 ml. of distilled water. To this solution the selected carbohydrate is added in 

 the desired quantity and when solution is complete the medium is distributed in 

 fermentation tubes. Sterilize by autoclaving for not more than 15 minutes at 15 



