DEHYDRATED CULTURE MEDIA 125 



to many highly enriched media with complicated formulae and methods of 

 preparation. 



Bacto-Dextrose Starch Agar prepared in half strength is an excellent medium 

 for maintaining stock cultures of the gonococcus. In tubes of this medium the 

 gonococcus generally remains viable for 6-8 weeks at 37°G. This medium cannot 

 be recommended to carry stock cultures of organisms capable of attacking 

 starch; some streptococci, for example, produce sufficient acid from the starch 

 in the medium to make it unsatisfactory for this purpose. Bacto-Stock Culture 

 Agar or Bacto-Cooked Meat Medium as discussed on page 98 and 85, is recom- 

 mended for the maintenance of starch hydrolyzing organisms. 



To rehydrate the medium suspend 65 grams of Bacto-Dextrose Starch Agar in 

 1000 ml. of cold distilled water, and heat to boiling to dissolve the medium com- 

 pletely. Distribute in tubes or flasks and sterilize in the autoclave for 15 minutes 

 at 15 pounds pressure (121°C.). For carrying stock cultures the medium is 

 prepared in the same manner, except that only 32.5 grams of Bacto-Dextrose 

 Starch Agar are used in 1000 ml. of cold distilled water. The medium normally 

 contains a flocculent precipitate which in no way detracts from the value of the 

 medium. Final reaction of the medium will be pH 7.3. 



Since best results are obtained with a solid medium having a moist surface, 

 Dextrose Starch Agar should be used the same day it is prepared, or if not used 

 at once, the medium should be melted and allowed to re-solidify just prior to 

 inoculation. It is recommended that sterile rubber stoppers be substituted for 

 the cotton plugs as soon as the slants have cooled. Screw-cap tubes also yield 

 satisfactory results. Cultures of gonococci on plates should be incubated in an 

 atmosphere saturated with moisture as indicated above. 



One pound of Bacto-Dextrose Starch Agar will make 7 liters of medium or 14 

 liters of half-strength medium. 

 lAm. J. Med. Tech., 14:214:1948. 



BACTO 



DEXTROSE AGAR (B67) 



DEHYDRATED 



Bacto-Beef Extract 3 g. 



Bacto-Tryptose 10 g. 



Bacto-Dextrose 10 g. 



Sodium Chloride 5 g. 



Bacto-Agar 15 g. 



Bacto-Dextrose Agar is recommended as a solid medium for cultivation of a 

 large variety of organisms and is especially adapted to the preparation of a 

 Dextrose Blood Agar. In deep tubes, or with removal of oxygen, it will support 

 good growth of anaerobes. 



Dextrose (<i-glucose) is a readily available source of energy, utilized by a large 

 number of microorganisms. This fact makes Dextrose Agar excellently suited for 

 the production of early and abundant growth, shortening lag periods of old 

 cultures and the initiation of growth of bacteria capable of utilizing dextrose. 

 Bacto-Dextrose Agar contains 1.0 per cent dextrose with a combination of other 

 ingredients that make an excellent Dextrose Agar capable of supporting growth 

 of all the more common bacteria and, in addition, such organisms as strepto- 

 cocci, pneumococci and meningococci. Norton^ recommended an agar medium 

 containing 0.5 to 1.0 per cent dextrose and about 5 per cent defibrinated blood 

 as being valuable for the isolation of organisms from pus, as well as being an 



