88 DIFCOMANUAL 



If Blood Agar is to be prepared immediately, the sterile medium is cooled at 

 once to 45-50° C. and while still liquid 5 per cent sterile defibrinated blood is 

 added aseptically with thorough mixing, avoiding incorporation of air bubbles, 

 and distributing in sterile tubes or plates as desired. Blood Agar for study of 

 cultural characteristics of colonies should be incubated to insure sterility before 

 use. 



Since most microorganisms prefer a fresh medium with a moist surface, it is 

 recommended that the Heart Infusion Agar be prepared as required, or melted 

 and re-solidified just prior to use. Blood Agar from this medium should be pre- 

 pared as required. 



One pound of Bacto-Heart Infusion Agar will make 11.3 liters of medium. 



1 Methods and Standards for the Production ^ J. Infectiom Diseases, 23:169:1918. 



of Certified Alilk, 28:1933-1954. 



BACTO 



BLOOD AGAR BASE (B45) 



DEHYDRATED 



Beef Heart, Infusion from, 500 g. 



Bacto-Tryptose 10 g. 



Sodium Chloride 5 g. 



Bacto-Agar 15 g. 



Bacto-Blood Agar Base is recommended as a base to which blood may be 

 added for use in the isolation and cultivation of many fastidious pathogenic 

 microorganisms. The slightly acid reaction of this medium is conducive to the 

 preservation of red blood cells. Without the addition of blood, this medium can 

 be recommended as a slightly acid agar medium for general laboratory work. 

 Many microorganisms produce earlier and more abundant growth on Blood 

 Agar with a slightly alkaline reaction, and therefore the use of this same medium 

 at pH 7.4, Bacto-Heart Infusion Agar as discussed immediately above or Bacto- 

 Tryptose Blood Agar Base discussed on page 115, is preferred. 



Colonies of bacteria upon a Meat Infusion Blood Agar usually grow luxuri- 

 antly, and the hemolytic types exhibit clear distinct degrees of hemolysis. Nor- 

 ton^ has recommended the use of such a medium with a reaction of pH 6.8 as 

 being distinctly advantageous in culturing the pneumococcus and streptococcus 

 groups. This slightly acid reaction seems to permit the development of clearer 

 zones of hemolysis than does an alkaline reaction. Bacto-Blood Agar Base is a 

 medium containing the extractives from fresh beef heart with Bacto-Tryptose. 

 This medium, which contains no added carbohydrate, is especially recom- 

 mended for use in the preparation of Blood Agar to study the hemolytic char- 

 acteristics of colonies. It is also recommended for isolation of organisms directly 

 from the blood. Bacto-Blood Agar base is mentioned in "Diagnostic Procedures 

 and Reagents"^ as an excellent basal medium for plate cultures for the pneu- 

 mococci. The use of 1 ml. of venipuncture blood in a sterile petri dish to which 

 is added the sterile cooled medium is recommended. The blood culture method 

 of Castaneda, as described in detail on page 113 under Tryptose Agar may be 

 used with this medium. 



Tarshis and Frisch^ investigated the addition of bank blood to various media 

 for the cultivation of tubercle bacilli in pure culture and directly from sputa 

 under routine diagnostic conditions. Three standard tuberculosis media were 

 used in the comparative study. They recommended the addition of 25 per cent 

 bank blood to Bacto-Blood Agar Base or Bacto-Bordet Gengou Agar Base with 1 

 per cent glycerol added since media of this type grew tubercle bacilli from small 



