84 DIFCOMANUAL 



Kracke and Teasley^ made an exhaustive study of the methods of blood cul- 

 turing and described a new medium which yielded relatively higher percentages 

 of positive cultures than other methods commonly employed. In their medium 

 the finely divided particles of brain and heart tissue aid in fixing the comple- 

 ment and in removing immune bodies from the blood specimen. The sodium 

 citrate prevents the blood from clotting and also aids in fixing the complement. 

 They used their medium in 50 ml. quantities in flasks and added 10 to 15 ml. 

 of blood specimen. Cultures were incubated for 18 hours at 37°C., and if nega- 

 tive at that time, reincubated for 3 weeks, with frequent observations for growth, 

 before being considered negative. 



Since the publication of their paper, Dr. Kracke has made a revision of the 

 formula (personal communication) resulting in a medium which would give 

 more satisfactory results. Bacto-Kracke Blood Culture Medium is prepared ac- 

 cording to this revision. 



Feder^ gave in detail a new and simplified technique for blood culturing. He 

 recommended the use of Bacto-Kracke Blood Culture Medium. 



Bacto-Kracke Blood Culture Medium when properly prepared, contains about 

 50 per cent solid meat particles. The supernatant liquid is frequently quite 

 turbid due to the presence of some of this very finely divided tissue. In blood 

 culture w^ork it may be necessary to prepare smears or make a transfer to an- 

 other medium in order to determine the presence of organisms. Bacto-Brain 

 Heart Infusion with PAB and Agar as discussed on page 79, can be recom- 

 mended as a clear liquid medium for blood culture work. 



To rehydrate the medium, suspend 3.75 grams of Bacto-Kracke Blood Culture 

 Medium in 50 ml. of distilled water. The suspension, with frequent agitation, is 

 allowed to stand for at least 15 minutes or until all the particles are thoroughy 

 wetted. It is essential that this step be adhered to closely, since the final medium 

 will not be sterile unless all the meat particles are thoroughly wetted before 

 heating. Maintain an even suspension of the meat particles if distributed in 

 tubes. The medium is then sterilized in the autoclave for 15 minutes at 15 pounds 

 pressure (121°C.). 



Special precautions must be taken to prevent too quick a decrease in pressure 

 at the end of the sterilization period, since a too rapid cooling of the autoclave 

 produces a vigorous boiling of the medium which results in excessive turbidity 

 of the supernatant liquid and may even occasionally blow the medium and plugs 

 from the flasks. The final reaction of the medium will be pH 7.4. 



For best results, this medium should be freshly prepared, or if not used the 

 same day as sterilized, heat in boiling water or flowing steam for a few min- 

 utes and cool quickly without agitation, just prior to inoculation. 



One pound of Bacto-Kracke Blood Culture Medium will make 6 liters of 

 medium. 



ij. Lab. Clin. Med., 16:169:1930. 2 J. Lab. Clin, Med., 22:846:1937. 



BACTO 



EGG MEAT MEDIUM (B42) 



DEHYDRATED 



Beef Muscle 454 g. 



Egg White from 6 eggs 



Calcium Carbonate 5 g. 



Bacto-Egg Meat Medium is a liquid medium containing particles of meat, egg 

 white and calcium carbonate in suspension. It is recommended for the deter- 



