INDOL PRODUCTION BY BACTERIA 



JOHN F. NORTON and MARY V. SAWYER 

 From the Department of Hygiene and Bacteriology, The University of Chicago 



Received for publication January 11, 1921 



The formation of indol in certain culture media has long been 

 considered an important differential characteristic for the iden- 

 ification of bacteria. Special interest in the test has been recently- 

 aroused in connection with investigations on respiratory diseases 

 because Pfeiffer's bacillus appears to be practically the only- 

 mouth organism producing indol (Jordan, 1919, Malone, 1920) ; in 

 consequence of which Malone has suggested that the test be used 

 as an index of the presence of this organism without actually iso- 

 lating it. Rivers (1920) has made a similar suggestion for 

 diagnosis of influenzal meningitis. For this paper we have 

 attempted to collect from the literature the more recent informa- 

 tion, both positive and negative, concerning indol production by 

 bacteria. On account of the uncertainty- of indol tests much of 

 the older work is unreliable. This information has been supple- 

 mented by tests on over 180 strains of bacteria, most of which are 

 being carried as stock cultures in this laboratory and have been 

 collected from a great variety of sources. Incidentally we 

 have made a comprehensive comparison of three recommended 

 media and also determined the effect of the incubation period 

 on indol production. 



MEDIA 



Indol is a disintegration product of proteins containing the 

 tryptophane group. The ideal medium would therefore be one 

 to which pure trytophane had been added but on account of the 

 difficulty of obtaining the material it is impractical, although 

 Zipfel (1913) used such a medium. Dunham's pepton is the 

 easiest medium to prepare and has been most frequently used. 



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