40 DIFCOMANUAU 



non-inhibitive selective agent for members of the coliform group. Optimum 

 results were obtained by the addition of 1:10,000 sodium lauryl sulfate to the 

 buffered Tryptose Lactose Broth. In their comparative study in the checking of 

 various types of water it was shown that the Lauryl Sulfate Tryptose Broth 

 (Bacto-Lauryl Tryptose Broth) gave a higher colon index than did the confirm- 

 atory "Standard Methods" media, and that gas production in the Lauryl Tryp- 

 tose Broth served not only as a presumptive test, but was also confirmatory of 

 the presence of the coliform group for routine testing of water. 



In a study of the coliform bacteria from chlorinated waters Levine^ compared 

 Lactose Broth and Lauryl Tryptose Broth. The latter medium gave fewer false 

 positive presumptive tests than did Lactose Broth and suppressed the spore form- 

 ing aerogenic bacteria. However, organisms showing a delayed fermentation of 

 lactose were not eliminated by Lauryl Tryptose Broth. 



Bacto-Lauryl Tryptose Broth was studied by 17 collaborating laboratories 

 situated throughout the United States and Canada. The results of this compara- 

 tive survey are reported by McCrady^. The study comprised the use of different 

 types of water and embraced different methods of treatment of samples. The re- 

 sults showed that the substitution of Lauryl Tryptose Broth for "Standard Meth- 

 ods" Lactose Broth would result in a reduction in the number of primary gas 

 positives to be confirmed, and an increase in the number of positive coliforms. It 

 was recommended that further study be made by different laboratories with par- 

 ticular reference to use of the medium in the examination of finished waters. 



Perry and Hajna'' in a comparative study of E G Medium and Lauryl Tryp- 

 tose Broth reported both media to be highly sensitive and specific for coliform 

 bacteria from water, shellfish and sewage. A positive presumptive test with either 

 medium was more dependable than the usual "confirmed" or "completed" test. 



The Ninth Edition of "Standard Methods for the Examination of Water and 

 Sewage" permits the substitution of Lauryl Tryptose Broth for Lactose Broth in 

 the standard tests for members of the coliform group in the examination of all 

 waters except final filtered, treated and filter-treated waters: "It may be sub- 

 stituted for lactose broth also in the examination of final filtered, treated and 

 filtered-treated waters provided the laboratory worker has amply demonstrated 

 by correlation of positive completed tests (isolations of coliform organisms) 

 secured through the use of lauryl sulfate tryptose broth with those secured 

 through the use of lactose broth, in the examination of such waters, that the 

 substitution results in no reduction from the density of coliform organisms indi- 

 cated by the standard procedure using lactose broth"^. 



Bacto-Lauryl Tryptose Broth duplicates the formula described by Mallmann 

 and Darby^ and specified in "Standard Methods for the Examination of Water 

 and Sewage," Ninth Edition^. It may be prepared in single strength when ex- 

 amining 1 ml. or less of water as an inoculum. For inocula of 10 ml. consult the 

 table given below. 



Concentration of Dehydrated Medium Required 

 to Maintain the Proper Concentration of Ingredients 



Bacto-Lauryl 

 Amt. Medium Vol. Medium Tryptose Broth 



Inoculum in Tube and Inoculum used per 1000 ml. 



1 ml. or less 10 ml. 10 ml. 35.6 g. 



10 ml. 20 ml. 30 ml. 53.4 g. 



10 ml. 30 ml. 40 ml. 47.3 g. 



