DEHYDRATED CULTURE MEDIA 153 



about 6 per cent of the population. A complete discussion of Bacto-Coagulase 

 Plasma is given on page 330. 



To rehydrate the medium, suspend 149 grams of Bacto-Staphylococcus 

 Medium No. 110 in 1000 ml. 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.). When cool enough to handle, 

 but hotter than the usual pouring temperatures, disperse the precipitate by gentle 

 agitation, avoiding air bubbles and pour into plates. If plates are not used when 

 poured, keep in refrigerator in sealed cans. For field work the medium may be 

 boiled for 5 minutes without further sterilization and poured into the plates, 

 preferably while still hot. The final reaction of the medium will be pH 7.0. 



One pound of Bacto-Staphylococcus Medium No. 110 will make 3 liters of 

 medium. 



^ Zentr. Bakt. I Abt. Orig., 149:122:1942. ^ J. Bact., 51:405:1946. 



2 J. Bact., 50:201:1945. 8 Am. J. Vet. Res., 8:275:1947. 



3 Am. J. Vet. Res., 8:173:1947- ^^ J- Bact., 55:793:1948- 



* Proc. See. Exp. Biol. Med., 33:185:1935. ^ J. Milk and Food Tech., 13:226:1950. 



5 Food Research, 2:349:1937- ^ J- Bact., 53:367:1947-. 



^ J. Bact., 51:409:1946. ^ Personal Communication. 



'Trans. N. Y. Academy Sciences, 9:52:1946. ^^ J. Bact., 63:147:1952. 



BACTO 



CHAPMAN STONE MEDIUM (B313) 



DEHYDRATED 



Bacto- Yeast Extract 2.5 g. 



Bacto-Tryptone 10 g. 



Bacto-Gelatin 30 g. 



£?-Mannitol, Difco 10 g. 



Sodium Chloride 55 g. 



Ammonium Sulfate 75 g. 



Dipotassium Phosphate 5 g. 



Bacto-Agar 15 g. 



Bacto-Chapman Stone Medium is a selective medium for the isolation of 

 staphylococci, prepared according to the formula described by Chapman.^ This 

 medium is similar to Bacto-Staphylococcus Medium No. 110 except that am- 

 monium sulfate is included in the medium and the amount of sodium chloride 

 reduced to 5.5 per cent. Flooding the plate with ammonium sulfate solution is 

 therefore unnecessary for the determination of Stone's method for the liquefac- 

 tion of gelatin. 



Sodium chloride is used as the selective agent in this medium. A complete 

 discussion of the use of high concentrations of this salt and details for the isola- 

 tion of staphylococci are given on page 151 under Bacto-Staphylococcus Medium 

 No. 110. In the examination of specimens, they are streaked on the surface of 

 the medium and incubated 48 hours at 30° G. Any yellow or orange colonies, 

 surrounded by a clear zone, which also ferment mannitol and are coagulase posi- 

 tive, are likely to be those of food poisoning or pathogenic staphylococci. White 

 or nonpigmented colonies, even though there may be a decided clear zone, are not 

 significant. 



Colonies showing any pigment production are picked from the surface of the 

 medium and emulsified in 0.1-0.2 ml. of Brain Heart Infusion or Tryptose Phos- 

 phate Broth for the performance of the coagulase test. A drop of brom cresol 

 purple indicator is added to several areas from which typical pigmented colonies 

 were removed. Any change in color of the indicator compared with that of the 

 uninoculated medium is indicative of the fermentation of mannitol. To determine 



