34 DIFCOMANUAL 



two different media need not be carried in stock. In "Standard Methods for the 

 Examination of Water and Sewage," Ninth Edition, 1946, page 191, it is stated that 

 experimental data indicate Bacto-Tryptone Glucose Extract Agar and Bacto- 

 Nutrient Agar give practically the same counts with water samples, and that 

 colonies are larger and more easily counted when the former medium is used. 



BACTO 



ENDO AGAR (B6) 



DEHYDRATED 



Bacto-Peptone 10 g. 



Bacto-Lactose 10 g. 



Dipotassium Phosphate 3.5 g. 



Bacto-Agar 15 g. 



Sodium Sulfite 2.5 g. 



Bacto-Basic Fuchsin 0.4 g. 



Bacto-Endo Agar is recommended for the confirmation of the presumptive 

 test for members of the coliform group in the bacteriological examination of 

 water, milk, and other dairy products, according to "Standard Methods for the 

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

 tion of Dairy Products."^ 



Endo^ originally described a medium using a fuchsin sulfite indicator to differ- 

 entiate lactose fermenting and lactose non-fermenting organisms of the intestinal 

 tract. Upon plates of this medium, in which the fuchsin has been decolorized by 

 sodium sulfite, typhoid and other lactose non-fermenting organisms appear as 

 clear, colorless, glistening drops against the faint pink background of the medium. 

 Coliform organisms fermenting lactose become red and color the surrounding 

 medium. The typical reactions of this medium are not caused by acid production 

 but by the intermediate product acetaldehyde, which is fixed by the sodium sul- 

 fite as was shown by Margolena and Hansen* and Neuberg and Nord.^ 



Endo's original formula has been subjected to many modifications, due largely 

 to variations in the available dyes and sulfites and to new uses of the medium 

 advocated by individual investigators. The result has been a multiplicity of varia- 

 tions of the formula. Harris^ investigated the problem of Endo Agar, studying 

 various ingredients, reaction, and available dyes. He reported that by using 

 Levine's modification'^ several sources of error were eliminated and that Bacto- 

 Peptone as recommended by Levine gave satisfactory results. In this modification 

 Dr. Harris found that a basic fuchsin composed of almost equal parts of rosanilin 

 and pararosanilin gave color reactions which were exceedingly sensitive and con- 

 sistent. Bacto-Endo Agar was developed in cooperation with Dr. Harris, conform- 

 ing to the Levine modification with the dye combination proposed by Harris. 



Endo Agar was originally developed for the isolation of typhoid bacilli. Since 

 that time more satisfactory media have been developed for this problem and 

 Endo Agar has proved of most value in the bacteriological examination of water. 

 Endo Agar and Levine Eosin Methylene Blue Agar are the two solid media 

 specified in the Ninth Edition of "Standard Methods for the Examination of 

 Water and Sewage" for the confirmation of the presence of coliform organisms 

 in Lactose Broth tubes giving a positive presumptive test. The formula used in 

 the preparation of Bacto-Endo Agar is identical with Formula II of "Standard 

 Methods for the Examination of Water and Sewage,"^ and since 1932 our label 

 has carried a statement to this effect. For the isolation of members of the Sal- 

 monella and Shigella group see Bacto-Bismuth Sulfite Agar, page 139; Bacto- 

 S S Agar, page 134; Bacto-MacConkey Agar, page 131; Bacto-Tetrathionate 



