34 CULTURE MEDIA 



FOR CONRADI-DRIGALSKI MEDIUM 



To ioo c.c. of lactose litmus agar add i c.c. of a solution of crystal violet (crystal 

 violet o.i gram, distilled water ioo c.c.). The medium is then ready to put into 

 plates. Colon colonies are pink. Typhoid and dysentery colonies, a bluish-gray. 



CONRADI'S BRILLIANT GREEN MEDIUM 



Take of Liebig's extract 20 grams (2%), peptone 10 grams (i%), agar 30 grams 

 (3%) and water to 1000 c.c. This amount of meat extract should give about the 

 proper acidity, +3. If not, the reaction should be adjusted to that point. Filter 

 through cotton, tube 150 c.c. amounts into 250 c.c. Erlenmeyer flasks and sterilize. 



Then add i c.c. of a i to 1000 aqueous solution of brilliant green (Hochst) and 

 i c.c. of a i% solution of picric acid to the flasks containing 150 c.c. of the melted 

 agar. Sterilization after adding the dyes precipitates them and is unnecessary. 

 Pour the finished medium into large Petri dishes and inoculate the surface with the 

 faeces. 



Brilliant green does not interfere with agglutination as does malachite green. 



This medium is considered by some authorities the one of choice in isolating 

 typhoid bacilli from fasces and urine. 



The surface of the poured plates of Endo, Conradi-Drigalski, and the brilliant 

 green media should be dried in the incubator before smearing with the fasces. For 

 routine work I prefer Endo's medium followed by Russell's double sugar agar. 



SELECTIVE MEDIA FOR CHOLERA 



Dieudonne's medium rests on the ability of cholera to grow when alkali is present 

 in such amounts as to inhibit the growth of other faecal bacteria. 



Take equal parts of defibrinated blood obtained at the slaughter house and 

 normal NaOH solution. Mix 30 parts of this alkaline blood mixture with 70 parts 

 of hot 3% nutrient agar. The poured plates should be left half open over night in 

 the incubator otherwise even cholera will not grow on the plates. 



Krumwiede has as a formula for his medium equal parts of whole egg and water, 

 to which 50% water egg mixture is added an equal amount of 12^% crystal sodium 

 carbonate solution. This alkaline egg mixture is steamed for twenty minutes. To 

 prepare add 30 parts of this alkaline egg mixture to 70 parts of meat extract free 

 3% agar. (No meat extract; only peptone and salt.) The cholera colony has a 

 hazy look, like a little wad of absorbent cotton sticking to the surface with a metallic 

 luster halo. 



Other selective media for cholera are those of Kabeshima in which a haemoglobin 

 extract is treated with alkalis and added to agar. 



The medium of Esch has been highly recommended. It is easy to make. Heat 

 500 grams chopped up beef with 250 c.c. normal NaOH solution in a pot and when 

 disintegrated filter through cloth and sterilize. About i part of this alkaline extract 

 is added to 2^ to 2 parts of agar. The plates must be dry. The transparency of 

 this medium is an advantage. 



