42 DIFCOMANUAL 



mended that it be used as a confirmatory medium. Bacto-Fuchsin Lactose Broth 

 is prepared according to the formula specified in "Standard Methods for the 

 Examination of Water and Sewage"^ and since 1936 our label has carried a 

 statement to that effect. 



To rehydrate the medium, dissolve 13 grams of Bacto-Fuchsin Lactose Broth in 

 1000 ml. of distilled water. The medium is distributed in fermentation tubes and 

 sterilized by autoclaving for 15 minutes at 15 pounds pressure (121°G.). The 

 final reaction of the medium will be pH 6.8. 



For water filtration plant control work, where the inoculum is greater than 1 

 ml., particular care must be taken to preserve the correct concentration of the 

 ingredients after dilution with the sample. For example, if 10 ml. of water are 

 to be added to 10 ml. of medium, the medium should be prepared in double 

 strength. 



One pound of Bacto-Fuchsin Lactose Broth will make 34.8 liters of medium. 



1 Standard Methods for the Examination ^ Am. J. Pub. Health, 27:1243:1937. 



of Water and Sewaee, gth Edition: 226:1946. * Standard Methods for the Examination 



*J. Am. Water Works Assoc, 24:413:1932. of Water and Sewage, 8th Edition: 204:1936. 



BACTO 



M.B.-B.G.P. MEDIUM (B21) 



DEHYDRATED 



Bacto-Beef Extract 5 g. 



Bacto-Peptone 7.8 g. 



Bacto-Lactose 4.7 g. 



Dipotassium Phosphate 1.7 g. 



Monopotassium Phosphate 0.3 g. 



Bacto-Erythrosin (L-D) 0.0064 g. 



Bacto-Methylene Blue (L-D) . . . 0.064 g. 



Bacto-Brom Cresol Purple 0.01 g. 



Bacto-M.B.-B.G.P. Medium has been suggested for the detection of coliform 

 bacteria in water supplies and is included in Appendix I of "Standard Methods 

 for the Examination of Water and Sewage"^ for use in parallel planting with 

 Lactose Broth in the control of water filtration plant operations. It is prepared 

 according to a modification of the original formula of Dominick and Lauter^ 

 and varies slightly from the formula in "Standard Methods for the Examination 

 of Water and Sewage."^ 



Dominick and Lauter^ devised the M.B.-B.C.P. Medium so as to decrease 

 the length of time required for determining the presence of coliform bacteria in 

 water. Their medium is essentially a buffered Lactose Broth to which a com- 

 bination of dyes has been added. The test depends upon reduction of methylene 

 blue by coliform organisms so that when the dye has been reduced the acid 

 (yellow) color of the brom cresol purple is brought to view. The dyes employed 

 inhibit lactose fermenting organisms w^hich are not members of the coliform 

 group. A positive test is generally assured within 24 hours incubation and a heavy 

 contamination will yield a positive test within 12 hours. The incubation of tubes 

 for 48 hours is recommended when they are not definitely positive after 24 hours. 

 The production of gas without the characteristic color change or, conversely, a 

 color change without gas production is regarded as a negative test. In the positive 

 test there must be gas accompanied by a typical color reaction. Bartram and 

 Black* found Bacto-M.B.-B.G.P. Medium to be the most productive of the 

 selective media used in their study of strains of Escherichia, Aerobacter, and inter- 

 mediates which had been recently isolated from raw milk. 



To rehydrate the medium, dissolve 19.6 grams of Bacto-M.B.-B.G.P. Medium 



