150 DIFGO MANUAL 



amined microscopically to determine the presence of organism having Corynebac- 

 terial characteristics. Mueller and Miller state that the morphology of the various 

 types of C. diphtheriae on the tellurite medium is entirely uniform. They further 

 suggest that the diphtheria organisms developing on this medium must be tested 

 for virulence or toxin production. 



About 20 ml. of the final medium are poured into plates. The surface of the 

 medium must be dry prior to inoculation; this is accomplished by allowing the 

 medium to cool and solidify with covers removed. The surface of the plate is 

 then streaked with the swab. A more selective medium for the initial cultivation 

 of Corynebacteria is described on page 147, prepared with Bacto-Dextrose Pro- 

 teose No. 3 Agar, enriched with Bacto-Tellurite Blood Solution. 



To rehydrate the medium, suspend 45 grams Bacto-Mueller Tellurite Base in 

 1000 ml. of cold distilled water. Heat to boiling to dissolve the medium com- 

 pletely. Sterilize in the autoclave for 10 minutes at 10 pounds pressure (116°G). 

 Cool to 50°C. and add 25 ml. Bacto-Mueller Tellurite Serum. Mix thoroughly 

 avoiding formation of air bubbles and distribute by pouring 20 ml. quantities in 

 sterile 95 mm. plates. Final reaction of the medium will be pH 7.6. 



One pound of Bacto-Mueller Tellurite Base will make 10.2 liters final medium. 



1 J. Bact., 51:743:1946. 



BACTO 



MANNITOL SALT AGAR (B30) 



DEHYDRATED 



Bacto-Beef Extract 1 g. 



Proteose Peptone No. 3, Difco . . 10 g. 



Sodium Chloride 75 g. 



<f-Mannitol, Difco 10 g. 



Bacto-Agar 15 g. 



Bacto-Phenol Red 0.025 g. 



Bacto-Mannltol Salt Agar is a selective medium for the isolation of pathogenic 

 staphylococci. It is prepared according to the formula suggested by Chapman.^ 

 Growth of most bacteria other than staphylococci is inhibited on this medium. 



Koch^ reported that on solid media staphylococci were not inhibited by a con- 

 centration of 7.5 per cent sodium chloride. Chapman^ confirmed this observation 

 and noted that the addition of 7.5 per cent sodium chloride to Bacto-Phenol Red 

 Mannitol Agar gave a medium on which staphylococci that coagulated rabbit 

 plasma grew luxuriantly, producing colonies with yellow zones. Nonpathogenic 

 staphylococci on the contrary produced small colonies surrounded by red or 

 purple zones. Other bacteria were generally inhibited, making possible the use of 

 a heavy inoculation without danger of overgrowth. Chapman recommended 

 incubation for 36 hours at 37°C. In a study of the resistance of chronic 

 staphylococcal bovine mastitis to massive penicillin therapy McCuUoch^ stated 

 that the staphylococci responsible for the mastitis grew well and formed acid in 

 Phenol Red Mannitol Agar to which 7.0 per cent sodium chloride had been 

 added. Velilla, Faber and Pelczar* used Bacto-Mannitol Salt Agar for the isola- 

 tion of coagulase producing staphylococci from milk in bovine mastitis. They 

 recommended the use of both Bacto-Mannitol Salt Agar and Bacto-Staphylo- 

 coccus Medium No. 110, to insure maximum recovery of these organisms. 



To rehydrate the medium suspend 111 grams Bacto-Mannitol Salt Agar in 

 1000 ml. cold distilled water, and heat to boiling to dissolve the medium com- 

 pletely. Distribute in tubes or flasks and sterilize in the autoclave for 15 minutes 



