PREPARATION OF MEDIA ii„-13 



extract, and 1% peptone) add 45 ml. of 1% aqueous ferric citrate containing 11% of 

 1% aqueous brilliant green, also 200 ml. of bismuth sulfite mi.xture prepared as follows: 

 dissolve 6 g. bismuth ammonium citrate scales in 50. ml. boiling water, and 20 g. 

 anhydrous Na^SOj in 100 ml. boiling water, mi.x, bring to a boil, and dissolve 10 g. 

 anhydrous Na2HP04 in the mixture while boiling, cool and add 10 g. glucose dissolved 

 in 50 ml. boiling water, restore lost water. After mixing these two solutions with the 

 melted agar pour immediately into petri dishes; after 1-2 hr. at room temperature 

 these plates may be stored in a refrigerator, but must be used within 4 days. 

 Use: Enrichment of typhoid and paratyphoid groups. 



Tellurite agar. (Anderson, et al. 1931). Add l}^ to 2 lbs. minced meat to 1000 

 ml. tap water at 48° C; after an hour squeeze out juice through cloth, leave in refrigera- 

 tor overnight and filter through filter paper. To 1000 ml. filtrate add 20 g. peptone 

 and 5 g. NaCl and dissolve at 45° C. Adjust reaction to pH 7.6. Filter first through a 

 Seitz K clarifying film; then sterilize by filtration through a sterile Chamberland candle, 

 collecting in sterile flasks and tubes. Incubate a few tubes for a check on sterility 

 but store the rest in a refrigerator. For use, mix with equal parts of 5% sterile agar 

 in water. Add 7-10% freshly drawn defibrinated rabbits' blood and 0.04% potassium 

 tellurite. Heat at 75° C for 10-15 minutes before pouring into plates. 



Use: DifiFerentiation of diphtheria organism. 



Desoxycholaie agar. (Lief son, 1935). 



Water 1000 ml. 



Peptone 10 g. Ferric ammonium citrate 2 g. 



Agar 12-17 g. K^HPO 2 g. 



NaCl 5 g. Sodium desoxycholate 1 g. 



Lactose 10 g. Neutral red (1% aqu. sol.) 3 ml. 



Dissolve the peptone in the water, adjust to pH 7.3-7.5, boil briefly and filter through 

 paper. Add the agar and dissolve by autoclaving; add 6 ml. of N NaOH, then the other 

 ingredients in the order named, omitting the neutral red until after a final adjustment 

 of the reaction to 7.3 or 7.5 as desired. Sterilize by heating in flowing steam only long 

 enough (i.e. about 15 minutes) to kill vegetative cells. 

 Use: Isolation of colon organisms from milk. 



Desoxycholate-citrate agar. (Liefson, 1935). Mix 333 g. fresh, lean, ground pork 

 with 1000 ml. distilled water and allow to infuse for about an hour; add 3.3 ml. N HCl 

 and boil for about one minute; filter through paper and add 3.3 ml. N NaOH; boil for 

 one minute and filter through paper; bring volume up to 1000 ml. by adding distilled 

 water. Add 10 g. peptone and adjust reaction to about pH 7.5. Boil 2-3 minutes and 

 filter through paper; then add 20 g. agar and 5 ml. N NaOH; after at least 15 minutes 

 standing, melt agar by boiling or autoclaving. Add as rapidly as possible in the follow- 

 ing order: 10 g. lactose, 25 g. sodium citrate (NajCaHjOj-l-o^HjO), 3.5 mg. PbClj 

 (optional). Just before using, and while melted and held at a temperature of 80- 

 100° C, add 0.2% ferric ammonium citrate (green scales); adjust reaction to pH 74. 

 and add to each 100 ml. 0.2 ml. of 1% aqueous neutral red. (It is important that the 

 temperature of the medium at the time should be high enough to kill vegetative cells.) 

 Pour into plates without further sterilization. 



Use: Isolation of typhoid organism from milk. 



