IMPORTANT PATHOGENIC BACTERIA 1 15 



(3) A few drops of a solution of o. i g. potassium or 

 sodium nitrite in 1,000 c.c. water. Rose color then 

 indicates the presence of indol only. 



The appearance of indol red depends on the pres- 

 ence of NO3. This is liberated by sulphuric acid 

 from nitrites, if these are produced by the organism. 

 If nitrites are not produced, a small amount of a nitrite 

 solution is added, which then furnishes the necessary 

 material for production of NO2. 



Perform these tests with all the organisms of the 

 intestinal group, and make control tests in sterile Dun- 

 ham's solution or sugar-free broth. 



4. Special study. — Make a capsule stain of B. 

 aerogenes from 24-hour-old milk cultures. (For 

 method see p. 109.) 



The study of B. coli is of special importance in con- 

 nection with bacteriological analysis of water (see 

 Part IV). The presence of this organism in large 

 numbers indicates sewage contamination, and conse- 

 quently bacteria such as B. typhosus and B. dysen- 

 teriae may be present. 



EXERCISE 2. STUDY OF SUBGROUP II 

 THE HOG-CHOLERA, B. ENTERITIDIS, OR INTERMEDIATE GROUP 



Inoculate agar slants from laboratory cultures of B. 

 suipestifer, B. enteritidis (Gartner's bacillus), and 

 B. paratyphosus. 



References — 



B. cholerae suis: 

 Moore, The Pathology of Infectious Diseases of Animals. 

 McFarland, Textbook of Bacteriology. 

 B. paratyphosus: 

 Buxton, Jour. Med. Res., igo2, 7, p. 201. 



