158 DIFCO MANUAL 



tubes, exercising care to obtain an even distribution of the insoluble material. 

 Do not heat after the iodine has been added. The complete medium containing 

 iodine should be used the day it is prepared, the base medium without the iodine 

 can be stored indefinitely after sterilization. 



One pound of Bacto-Tetrathionate Broth Base will make 9.8 liters of base 

 medium. 



1 Standard Methods for the Examination of ^Zeit. Hyg., 117:26:1935-36. 



Dairy Products, gth Edition: 165:1948. « Zentr. Bakt., I Abt., Orig., 133:458:1935. 



3 Diagnostic Procedures and Reagents, 3rd Edi- "^ J. Path. Bact., 42:455:1936. 



tion: 212: 1950. 8 Brit. Med. J., 1:606:1940. 



3 Compt. rend. soc. biol., 89:434:1923. ^ Comp. rend. soc. biol., 118:1675:1935. 



*Zentr. Bakt., I Abt., Orig., 113:148:1930-31. ^o J. Milk and Food Tech., 13:226:1950. 



BACTO 



SELENITE BROTH (B275) 



DEHYDRATED 



Bacto-Tryptone 5 g. 



Bacto-Lactose 4 g. 



Disodium Phosphate 10 g. 



Sodium Selenite 4 g. 



Bacto-Selenite Broth is recommended as an enrichment medium in the 

 isolation of Salmonella typhosa and other members of the Salmonella group 

 from feces, urine and infected tissues. The formula of this medium is essentially 

 the same as that of Selenite F Broth described by Leifson.^ Selenite Broth, for 

 the enrichment of enteric pathogens, is described in "Diagnostic Procedures and. 

 Reagents."^ 



Handel and Theodorascu according to Guth^ observed that Escherichia coli 

 was much more susceptible to the toxicity of sodium selenite than was S. typhosa. 

 Guth^ confirmed the observations of these authors and employed sodium selenite 

 SIS a selective agent in an agar medium and in an enrichment broth for the 

 isolation of S. typhosa from feces. Leifson^ extended Guth's observations and 

 developed a Selenite Agar and a Selenite Broth for use in the isolation of typhoid 

 and paratyphoid bacilli from feces and urine and found the broth enrichment 

 to offer the greater promise. 



Leifson showed that the Selenite Broth was not sufficiently toxic to inhibit 

 fecal coli and enterococci completely. However, the colon bacilli were reduced 

 in numbers during the first 8-12 hours and thereafter increased rapidly. The 

 typhoid bacilli on the other hand multiplied fairly rapidly from the start. Proteus 

 and pyocyaneus were not inhibited. Dysentery and alcaligenes were inhibited. 

 In the Selenite Broth the growth behavior of coli and typhoid in the presence of 

 feces or urine was similar to that of pure cultures. 



Leifson observed that the selenite medium functioned most efficiently under 

 reduced oxygen tension. To provide optimal conditions, the broth was distributed 

 in tubes to give a depth of 2 inches or more. Using the enrichment under optimal 

 conditions Leifson was able to isolate many more typhoid and paratyphoid 

 organisms than by direct plating without primary enrichment. 



In a survey of methods used for the collection and preservation of stool speci- 

 mens for the isolation and identification of Salmonella, Shigella and intestinal 

 protozoa, Felsenfeld* reported an increasing number of laboratories using the 

 Selenite Broth as an enrichment. In a study of methods to be used as a standard 

 for the bacterial examination of pullorum reactors, Jungherr, Hall and Pomeroy^ 

 in a committee report showed that in a comparative study of media and enrich- 

 ments, from October, 1946 to February, 1950, Bismuth Sulfite Agar and S S Agar 



