186 DIFCO MANUAL 



ml. of cold distilled water and heat to boiling to dissolve the medium completely. 

 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 6.8. 

 One pound of Bacto-Nitrate Agar will make 21 liters of medium. 



BACTO 



PHENOL RED BROTH BASE (B92) 



DEHYDRATED 



Bacto-Beef Extract 1 g. 



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



Sodium Chloride 5 g. 



Bacto-Phenol Red 0.018 g. 



Bacto-Phenol Red Broth Base, and the complete carbohydrate* media de- 

 scribed below, are used in fermentation studies for the cultural identification of 

 pure cultures of microorganisms. The fermentative properties of bacteria are 

 valuable criteria in their identification, and may be determined by culturing the 

 organisms in a suitable medium containing the appropriate fermentable substance. 

 A satisfactory basic medium for determining the fermentation reactions of micro- 

 organisms must be capable of supporting growth of the organisms under study, 

 and free from fermentable carbohydrates which could give erroneous interpreta- 

 tions. It must be stable, uniform in composition, give distinct reactions and yield 

 accurate results. 



Bacto-Phenol Red Broth Base is an excellent substrate for streptococci, 

 pneumococci, meningococci and gonococci, as well as for other less fastidious 

 types. The cultural value of the medium can be greatly improved for some of the 

 more delicate strains by the addition of a small amount (0.1-0.2 per cent) of 

 Bacto-Agar. A medium containing this small quantity of agar may be used to 

 best advantage by heating it to the boiling point to drive out the dissolved air and 

 cooling it below 40° C, without excessive agitation, just previous to inoculation. 

 Such a procedure also makes the medium sufficiently oxygen-free for propagation 

 of the obligate anaerobes as well as microaerophiles. Bacto-Phenol Red Broth 

 Base with 0.5 per cent selected carbohydrate and 0.15 per cent agar is suggested 

 as a satisfactory medium for the fermentation determinations as given in Diag- 

 nostic Procedures and Reagents.^ Some bacteriologists, determining the fer- 

 mentation reactions of gonococci, may prefer to use 0.8 per cent Bacto-Agar and 

 add 5 per cent sterile fresh rabbit serum to the sterile Phenol Red Broth con- 

 taining the selected carbohydrate, as discussed under Bacto-Proteose No. 3 Agar, 

 page 116. 



For the determination of fermentative properties of members of the enteric 

 group of bacteria, Bacto-Purple Broth Media are recommended, as discussed on 

 page 190. These media have the same nutrients, but have a slightly more acid 

 reaction, and brom cresol purple is employed as an indicator. 



With the exception of the carbohydrate, which has been omitted, Bacto-Phenol 

 Red Broth Base is a complete basic medium prepared with phenol red as an 

 indicator of changes in reaction. This product makes it possible to prepare as 

 much or as little medium as is required, adding to different portions any ferment- 

 able substance in any concentration desired. The concentration of carbohydrate 

 generally employed for testing the fermentation 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 carbo- 



*The term carbohydrate, as used here, includes carbohydrates, polyhydric alcohols, glucosides and 

 other fermentable carbon compounds. 



