32 DIFCOMANUAL 



BACTO 



NUTRIENT GELATIN (Bll) 



DEHYDRATED 



Bacto-Beef Extract 3 g. 



Bacto-Peptone 5 g. 



Bacto-Gelatin 120 g. 



Bacto-Nutrient Gelatin is recommended for the 20°C. plate count of water 

 according to "Standard Methods for the Examination of Water and Sewage"^ 

 of the American Public Health Association and the American Water Works Asso- 

 ciation. It is also recommended for the determination of gelatin liquefaction in 

 the identification of anaerobes and other microorganisms. 



Gelatin was one of the first solidification agents used in the science of bac- 

 teriology, enabling the direct plate count to be used rather than the dilution 

 method for determination of bacterial populations, and for the isolation of pure 

 cultures. However, there are certain limitations to the use of gelatin in plating 

 and isolation procedures, as incubation must be carried out at approximately 

 20° C., a temperature lower than the optimum for many organisms. Further, 

 many organisms have the ability to attack and liquefy the gelatin. Although 

 Nutrient Gelatin is still used in the plate count of water with incubation at 

 19-2 1°C., plating procedures now most generally utilize media containing agar 

 as a solidifying agent. The chief use of Nutrient Gelatin is for the detection of 

 proteolysis (the elaboration of gelatinolytic enzymes) as evidenced by the lique- 

 faction of gelatin. 



Bacto-Nutrient Gelatin is prepared according to the formula specified in 

 "Standard Methods" and since 1925 our label has carried a statement to that 

 effect. Plates are incubated at 19-21 °C. for 48 hours and the colonies counted. 

 In determining gelatin liquefaction of pure cultures in this medium, tubes are 

 incubated for at least five days at 19-21°C. If the optimum temperature for the 

 organism in question is above 20°C., incubate at the desired temperature and 

 after incubation cool the tubes to 20 °C., to determine if the gelatin has been 

 liquefied. 



To rehydrate the medium, suspend 128 grams of Bacto-Nutrient Gelatin in 

 1000 ml. of cold distilled water and warm to about 50° C. 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-Nutrient Gelatin will make 3.5 liters of medium, 



1 Standard Methods for the Examination of Water and Sewage, gth Edition: 186:1946. 



BACTO 



NUTRIENT AGAR ( B 1 ) 



DEHYDRATED 



Bacto-Beef Extract 3 g. 



Bacto-Peptone 5 g. 



Bacto-Agar 15 g. 



Bacto-Nutrient Agar is recommended for the examination of water according 

 to "Standard Methods for the Examination of Water and Sewage"^ of the Ameri- 

 can Public Health Association and the American Water Works Association. It is 

 also recommended as a general culture medium for the cultivation of the majority 

 of the less fastidious microorganisms, as well as a base to which a variety of 

 materials are added to give selective, differential, or enriched media. 



