146 DIFCO MANUAL 



BACTO 



PURPLE LACTOSE AGAR (B82) 



DEHYDRATED 



Bacto-Beef Extract 3 g. 



Bacto-Peptone 5 g. 



Bacto-Lactose 10 g, 



Bacto-Agar 10 g. 



Bacto-Brom Cresol Purple 0.025 g. 



Bacto-Purple Lactose Agar like Litmus Lactose Agar has been used in water 

 bacteriology and in other examinations for the detection of members of the coli- 

 form group. This medium may also be used for the determination of the fer- 

 mentation of lactose with the production of acid and gas. 



The disadvantages resulting from the use of litmus in culture media are well 

 known. Litmus has been replaced quite generally by the more stable and sensitive 

 sulfonephthalein indicators which are more sensitive to slight changes in hydro- 

 gen ion concentration. 



Bacto-Purple Lactose Agar duplicates the formula of Bacto-Litmus Lactose 

 Agar except that brom cresol purple has been substituted for the litmus in order 

 to provide a more satisfactory differential between colonies of the lactose fer- 

 menting bacteria and those which do not attack lactose. The color change of 

 this indicator is from blue-purple (alkaline) to yellow (acid). The medium is 

 used for the same purposes and in the same manner as Litmus Lactose Agar. 

 Inoculated plates should be observed frequently after the first 18-24 hours in- 

 cubation to avoid confusing results due to diffusion of the acid through the 

 medium. 



Bacto-Violet Red Bile Agar as discussed on page 61 is recommended for use 

 in making coliform counts of water, milk, dairy and other food products. Bacto- 

 Brilliant Green Bile Agar as discussed on page 52 is a most satisfactory medium 

 for coimts of the coliform bacteria in water. 



To rehydrate the medium, suspend 29 grams of Bacto-Purple Lactose Agar in 

 1000 ml. of 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 

 at 15 pounds pressure ( 121°C.). The final reaction of the medium will be pH 6.8. 



One pound of Bacto-Purple Lactose Agar will make 15.6 liters of medium. 



BACTO 



CONRADI DRIGALSKI AGAR (B83) 



DEHYDRATED 



Bacto-Peptone 10 g 



Bacto-Isoelectric Casein 10 g 



Bacto-Lactose 10 g, 



Sodium Chloride 5 g 



Bacto-Agar 15 g 



Bacto-Brom Cresol Purple 0.03 g. 



Bacto-Crystal Violet 0.004 g 



Bacto-Conradi Drigalski Agar has been rather extensively employed in the past 

 for the isolation of typhoid and other intestinal pathogens from fecal specimens. 

 Media described subsequent to Conradi Drigalski Agar have proved more satis- 

 factory, and are now recommended for this purpose. For the present we will 

 continue to carry Bacto-Conradi Drigalski Agar for those laboratories where it 



