DEHYDRATED CULTURE MEDIA 133 



BACTO 



DESOXYCHOLATE AGAR 



DEHYDRATED 



A complete discussion of Bacto-Desoxycholate Agar as used for the isolation of 

 members of the Shigella and Salmonella groups is given on page 63. 



BACTO 



E.M.B. AGAR (B76) 



DEHYDRATED 



Bacto-Peptone 10 g 



Bacto-Lactose 5 g 



Saccharose, Difco 5 g 



Dipotassium Phosphate 2 g 



Bacto-Agar 13.5 g 



Bacto-Eosin Y 0.4 g 



Bacto-Methylene Blue 0.065 g 



Bacto-E.M.B. Agar, a differential plating medium, is recommended for the 

 detection and isolation of the Gram-negative intestinal pathogenic bacteria. 



The original Eosin Methylene Blue Agar was devised by Holt-Harris and 

 Teague.^ These workers employed a combination of eosin and methylene blue as 

 an indicator which gave a sharp and distinct differential between colonies of 

 lactose fermenting organisms and those which did not ferment lactose. These 

 authors included saccharose in their medium since certain members of the coli- 

 form group ferment this carbohydrate more readily than lactose. Colonies of the 

 coli-aerogenes group were either black or possessed dark centers with transparent 

 colorless peripheries, while those of typhoid and other organisms which did not 

 ferment lactose or saccharose remained uncolored. The Eosin Methylene Blue 

 Agar of Holt-Harris and Teague possessed definite advantages over the Fuchsin 

 Sulfite Agar of Endo, in that it was more sensitive, more accurate, more stable 

 and gave an earlier differentiation. 



Two years after Holt-Harris and Teague had introduced their new medium, 

 Levine- described an Eosin Methylene Blue Agar for the purpose of differentiat- 

 ing the fecal and non-fecal types of the colon-aerogenes group. Levine's medium, 

 as discussed on page 35, also differentiated the typhoid and other lactose non- 

 fermenters from the coliform organisms. 



Bacto-E.M.B. Agar is a combination of the Levine and the Holt-Harris and 

 Teague formulae. It contains Bacto-Peptone and phosphate as recommended by 

 Levine, and retains the two carbohydrates lactose and saccharose, as suggested by 

 Holt-Harris and Teague. The ratio of the two indicator dyes has been worked out 

 to give the best differentiation and minimum toxicity. This medium has all the 

 advantages of the original media referred to above. 



It is recommended that for the detection of the more fastidious Shigella and 

 Salmonella organisms, Bacto-MacConkey Agar, the selective Bacto-S S Agar and 

 Bacto-Bismuth Sulfite Agar, as discussed on pages 131, 134 and 139, be run in 

 conjunction with Bacto-E.M.B. Agar. 



To rehydrate the medium, suspend 36 grams of Bacto-E.M.B. Agar in 1000 ml. 

 of cold distilled water and heat to boiling to dissolve the medium completely. 

 Distribute in tubes or flasks and sterilize in the autoclave for 15 minutes at 15 

 pounds pressure (121°C.). Bacto-E.M.B, Agar inoculated the same day as re- 

 hydrated may be used without autoclave sterilization. Under these conditions 



