DEHYDRATED CULTURE MEDIA 45 



lize in the autoclave for 15 minutes at 15 pounds pressure (121°C.). The final 

 reaction of the medium will be pH 6.8. 



When the medium is to be used in 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-Eijkman Lactose Medium will make 15.9 liters of 

 medium. 



1 Standard Methods for the Examination * Food Research, 4:381:1939. 



of Water and Sewage, 9th Edition: 226: 1946. ^ Personal Communication, 1939. 



2 Centr. Bakt., II. Abt., 37:742:1904. « Standard Methods for the Examination 



3 J. Bact., 26:419:1933. of Water and Sewage, gth Edition: 232: 1946. 



BACTO 



E G MEDIUM (B314) 



DEHYDRATED 



Bacto-Tryptose 20 g. 



Bacto-Lactose 5 g. 



Bacto-Bile Salts No. 3 1.5 g. 



Dipotassium Phosphate 4 g. 



Monopotassium Phosphate 1.5 g. 



Sodium Chloride 5 g. 



Bacto-E C Medium conforms to the formula given by Hajna and Perry^ for the 

 medium described for the detection of coliform bacteria at 37°G. and of Escher- 

 ichia coli at 45.5°C. It can be used either as a primary medium for the growth of 

 E. coli or as a satisfactory secondary medium for E. coli confirmation. This selec- 

 tive broth may be used in parallel planting with Lactose Broth in the control of 

 water filtration plant operation as described in Appendix I of "Standard Methods 

 for the Examination of Water and Sewage."^ 



In an effort to improve further the methods for the detection of members of 

 the coliform group and E. coli Hajna and Perry^ developed E C Medium. This 

 medium consisted of a buffered Lactose Broth to which was added 0.15 per cent 

 of Bacto-Bile Salts No. 3. Growth of spore formers and fecal streptococci was 

 inhibited by the bile salts while growth of coli was enhanced by its presence. The 

 medium can be used at 37 °C. for the detection of coliform organisms or at 

 45.5 °C. for the isolation of E. coli. In a further evaluation study of the E G 

 Medium and Lauryl Tryptose Broth, Perry and Hajna^ reported the results ob- 

 tained from eleven different laboratories examining a variety of waters, milk, 

 and shellfish. The results indicated that these media were highly specific for 

 coliform bacteria. A presumptive test reading with the E G Medium or Lauryl 

 Tryptose Broth seemed more dependable than the usual "confirmed" or "com- 

 pleted" test for coliform bacteria. 



To rehydrate the medium, dissolve 37 grams Bacto-E G Medium in 1000 ml. 

 of distilled water. Sterilize in the autoclave for 15 minutes at 15 pounds pressure 

 (121°G.). Final reaction of the medium will be pH 6.9. 



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-E G Medium will make 12.2 liters of medium. 



lAm. J. Pub. Heahh, 33:550: i943- 3 Am. J. Pub. Health, 34:735:i944. 



* Standard Methods for the Examination 

 of Water and Sewage, 9th Edition: 226: 1946. 



