SUBSTITUTION OF BROM-THYMOL-BLUE FOR LITMUS 

 IN ROUTINE LABORATORY WORK 



H. R. BAlsER 



Contribution No. 44 from the Department of Bacteriology, Kansas State 

 Agricultural College 



Received for publication December 10, 1921 



One of the common methods for the qualitative determination 

 of acid or alkali production by bacteria is to inoculate nutrient 

 extract broth containing various carbohydrates with Utmus as 

 an indicator. 



Litmus possesses the disadvantage of being reduced by many 

 organisms to a colorless compound, thus rendering it useless as an 

 indicator. Clark and Lubs (1917) mention that the sulphon- 

 phthalin indicators are much more resistant to bacterial action 

 than indicators like methyl red or litmus. They suggest, be- 

 cause of certain preliminary tests, that indicators like brom- 

 thymol-blue and brom-cresol-purple might be used to advantage 

 in replacing other indicators which are now used in making indi- 

 cator media. 



With this suggestion in mind, an experiment was undertaken 

 to find a method of preparing media to determine qualitatively 

 acid or alkaU production by bacteria, which would be easy to 

 prepare, and more sensitive than litmus; and one in which the 

 reaction could be quickly determined at any time during the 

 . incubation period. 



In this experiment, sugar free broth was used, which was pre- 

 pared as follows : 



One pound of ground lean meat was digested for two hours with 

 1 liter of distilled water. After cooking, the broth was filtered 

 through absorbent cotton into a flask and steriMzed in the auto- 

 clave at 18 pounds pressure for twenty minutes. When cold the 

 broth was inoculated with a culture of Bad. saccharolyte (Rivas) 



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