142 DIFGO MANUAL 



in still larger numbers, typical blackening does not occur and the appearance is 

 that of a negative plate. 



Ordinarily typhoid will develop well isolated colonies showing typical round 

 jet black colonies with or without sheen, from either the 5 ml. or 1 drop inocula- 

 tion of cotton-filtered fecal suspension using the poured plate method. However, 

 the typhoid organisms developing from the specimens containing large numbers 

 of typhoid may be so numerous that the blackening cannot occur typically and 

 the plate may appear dotted black or greenish gray. From such heavily seeded 

 specimens the direct smear on Bismuth Sulfite Agar from feces should demon- 

 strate typhoid, while the poured plate should give positive results from specimens 

 containing lesser numbers of typhoid. 



Description of Colonies Other Than Typhoid 



S. schottmuelleri [Paratyphoid B) and S. enteritidis grow luxuriantly upon 

 Bacto-Bismuth Sulfite Agar forming black surface and subsurface colonies slightly 

 more moist, but otherwise similar to those produced by S. typhosa. 



S. paratyphi [Paratyphoid A), S. typhimurium, S. choleraesuis and Proteus 

 morganii develop upon Bacto-Bismuth Sulfite Agar, yielding fiat or only slightly 

 raised green colonies. 



Generally, the members of the dysentery group other than Flexner and Sonne 

 are inhibited. The Flexner and Sonne strains that do develop upon this medium 

 produce brownish raised colonies with depressed centers and exhibit a crater-like 

 appearance. 



Coli is usually completely inhibited. Occasionally a strain will be encountered 

 that will develop small black, brown or greenish glistening surface colonies. This 

 color is confined entirely to the colony itself and shows no metallic sheen. Like- 

 wise a few strains of aerogenes may develop on this medium forming raised, 

 mucoid colonies. These may exhibit a silvery sheen, appreciably lighter in color 

 than that produced by typhoid. Subsurface colonies of the coliform group, when 

 they develop, are green or brown in color, generally lenticular in shape, and not 

 at all to be confused with the typical round black typhoid subsurface colony. 

 There are some members of the coliform group capable of producing hydrogen 

 sulfide that may develop on the medium, giving colonies similar in appearance 

 to typhoid. These may readily be differentiated in that they produce gas from 

 lactose in differential media — Bacto-Russell Double Sugar Agar, Bacto-Kligler 

 Iron Agar or Bacto-Triple Sugar Iron Agar, for example. The hydrolysis of urea 

 as demonstrated on Bacto-Urea Broth or Bacto-Urea Agar, as discussed on pages 

 170 and 171, may be used to identify proteus or paracolon organisms. 



The isolation and purification of S. typhosa for agglutination or fermentation 

 studies may be readily accomplished by picking characteristic black colonies from 

 smeared or poured plates of Bismuth Sulfite Agar, and subculturing them upon 

 Bacto-MacConkey Agar. The purified colonies thus obtained may then be picked 

 to differential tube media such as Bacto-Russell Double Sugar Agar, Bacto- 

 Kligler Iron Agar, Bacto-Triple Sugar Iron Agar or other satisfactory differential 

 media for partial identification. Agglutination tests may be made from the fresh 

 growth on the differential tube media or from the growth on Nutrient Agar slants 

 inoculated from the differential media. The growth on the differential tube media 

 may also be used for inoculating carbohydrate media for fermentation studies. It 

 is a common practice among many bacteriologists to pick colonies typical of 

 S. typhosa directly from Bismuth Sulfite Agar onto the differential tube media. 

 This may be permissible if the colonies are discrete and well isolated, but it must 

 be remembered that although coliform bacteria are inhibited they are not de- 

 stroyed by the medium. 



