INGREDIENTS OF CULTURE MEDIA 269 



/.TRYPTOPHANE, DIFGO (B188) 



Tryptophane is an amino acid, essential for the growth of many micro- 

 organisms. Tryptophane is utilized by bacteria in the elaboration of indole and 

 has, therefore, been employed in media devised for testing for indole production. 



Since tryptophane is destroyed by acid hydrolysis, synthetic media employing 

 acid hydrolysates or chemically pure amino acid mixtures as sources of nitrogen, 

 require the addition of tryptophane for the growth of most bacteria. 



/-TYROSINE, DIFGO (B189) 



Tyrosine is an amino acid which has been used occasionally in the preparation 

 of culture media. 



EXTRACTS 



BAGTO-BEEF EXTRAGT (B126) 



Infusions of meat were first generally employed together with peptone as 

 nutriments in culture media. Later it was found that for many routine procedures 

 beef extract gave fully as good results and had the decided advantages of greater 

 ease of preparation, greater uniformity and economy. A medium composed of 

 beef extract, peptone and agar has been one of the most generally used media 

 in bacteriological procedures. 



Bacto-Beef Extract is prepared and standardized for use in microbiological 

 culture media, where it is generally used to replace infusions of meat. It is 

 standard in its composition and reaction, and does not require adjustment of 

 reaction or filtration. For many years beef extract media have been recom- 

 mended as standard for use in the routine bacteriological examination of water, 

 milk and other materials where it is important to have media of uniform 

 composition. 



Bacto-Beef Extract may be relied upon for biochemical studies, particularly 

 fermentation reactions because of its freedom from fermentable substances which 

 would interfere with the accuracy of such determinations. 



In culture media, Bacto-Beef Extract is usually employed in concentrations 

 of 0.3 per cent as in the standard media recommended for water and for milk 

 analysis.^'2 Concentrations may vary slightly according to the requirements of 

 individual formula, but do not often exceed 0.5 per cent. In 0.3 per cent con- 

 centration Bacto-Beef Extract forms brilliantly clear solutions, rich in the nutri- 

 ments required for bacterial metabolism. After autoclave sterilization this solution 

 has a reaction of pH 6.8. 



In the fields of special research Bacto-Beef Extract has been employed in 

 media by a number of investigators. Bedell and Lewis^ used it in their medium 

 for the study of the non-sporulating anaerobes of the intestinal tract, and Tittsler 

 and Sandholzer* employed it in carbohydrate broths for studying the cultural 

 characteristics of the Escherichia-Aerobacter intermediates. Hutner^ used a 

 medium containing Bacto-Beef Extract as a stock broth in his study of the 

 nutritional needs of the streptococci. Kent^ also employed Bacto-Beef Extract 



