DEHYDRATED CULTURE MEDIA 159 



permitted the highest number of specific isolations of S. pullorum and S. galli- 

 narum. These favored selective media suppressed the growth of coliform organ- 

 isms. Following enrichment of the specimens in Selenite Broth streaking on 

 Bismuth Sulfite Agar gave the largest number of positive isolations, followed by 

 S S Agar and then MacConkey Agar. Selenite Broth yielded a higher number of 

 successful isolations on follow-up media than did Tetrathionate Broth. The 

 highest percentage of organisms were isolated from the ovary, followed by gall 

 bladder, peritoneum, oviduct, intestines and pericardial sac in the order listed. 



For the examination of fecal specimens Selenite Broth is inoculated by adding 

 1-2 ml. of fecal suspension to tubes of 10-15 ml. of medium. After thorough 

 mixing, the tubes are incubated at 37°C. for 18-24 hours. For the examination 

 of infected tissues 1-2 grams of material are mascerated in 10-15 ml. Selenite 

 Broth by means of a sterile pipette or stirring rod before incubation. For exam- 

 ination of urine the Selenite Broth should be prepared in double strength and 

 tubed in 5-7.5 ml. amounts. This broth is inoculated with an equal volume of 

 urine sample and is incubated as described above. After incubation a loopful of 

 the enriched culture is streaked on one plate of Bismuth Sulfite Agar and a 

 similar amount is streaked on one plate of S S Agar. These plates are incubated 

 at 37 °C. and are examined after 18-24 hours. The Bismuth Sulfite Agar plate 

 should be incubated for 48 hours before being discarded as negative. 



To rehydrate the medium, suspend 23 grams Bacto-Selenite Broth in 1000 ml. 

 of distilled water and heat to boiling. Distribute in sterile culture tubes to give a 

 depth of medium of at least 2 inches. Avoid excessive heating. Do not sterilize in 

 the autoclave. The final reaction of the medium will be pH 7.0. 



One pound of Bacto-Selenite Broth will make 19 liters of medium. 



1 Am. J. Hyg., 24:423:1936. * Public Health Reports, 63:1075:1950. 



2 Diagnostic Procedures and Reagents, 3rd Edi- ^ Proc. 22nd Ann. Mtg. N. E. Conf. Lab. Work- 

 tion:25:i950. ers Pullorum Disease Control, Burlington, Vt., 



8 Centr. Bakt. I Abt. Orig., 77:487:1916. 1950. 



Differential Tube Media 



Differential tube media afford the bacteriologist a simple and effective cultural 

 means of identifying pure cultures of bacteria. Both solid media and liquid media 

 have been devised for this purpose. Many of the solid differential tube media 

 contain one or more fermentable carbohydrates and a suitable indicator for the 

 detection of acid or alkali production; some contain substances rich in sulfur 

 and an indicator to detect hydrogen sulfide formation; still others contain a 

 combination of both. The solid tube media containing fermentable carbohydrates 

 permit the study of both aerobic and anaerobic dissimilation processes by the 

 bacteria under study. Screw capped tubes are not satisfactory for solid differen- 

 tial media as pointed out by Marcus and Greaves^ unless the caps be placed on 

 the tubes loosely, or replaced by cotton plugs. The changes produced in the 

 media by an organism or group are characteristic, thus differentiating it from 

 other strains or groups. Differential semisolid media are used to demonstrate 

 motility and certain biochemical characteristics of microorganisms. Liquid differ- 

 ential tube media, in general, are employed in studying the fermentation reac- 

 tions of pure cultures of bacteria, or their ability to utilize certain nutriments. 



1 J. Lab. Clin. Med., 36:134:1950. 



