140 BIOLOGY AND TECHNIQUE 



THE INFLUENCE OF DYE STUFFS UPON BACTERIAL GROWTH, 

 AND AS ADDITIONS TO SELECTIVE MEDIA 



In describing the selective media for typhoid baciUi we have seen 

 that malachite green and crystal violet have been found to exert a 

 certain amount of selective action upon the typhoid and colon groups. 

 The selective influence of various dyes has been recently again studied 

 by Churchman. Churchman ^ found that the addition of gentian 

 violet in dilutions of 1 : 100,000, to media, inhibited some bacteria, while 

 others grew luxuriantly in its presence. Extremely interesting, both 

 practically and theoretically, is his observation that upon such gentian 

 violet media bacteria fall into two groups. Those which grow on 

 gentian violet correspond in a general way to the Gram-negative bacteria; 

 those which fail to develop on these media correspond roughly with the 

 Gram-positive species. One strain of the enteritidis group could not 

 be cultivated on gentian violet, and this was found to differ from the 

 others also in its agglutination tests. 



Signorelli ^ claims that dahha is useful in differentiating true cholera 

 strains from similar spirilla. The true cholera strains grew with colored 

 colonies, while others remain colorless, in his experiments. 



Krumwiede and Pratt ^ were unable recently to confirm the claims 

 of Signorelli. However they fully confirm the findings of Churchman 

 both as to the selective action of gentian violet and in regard to the 

 classification of bacteria into two groups corresponding to their reaction 

 to the Gram stain. They state that among Gram-negative bacteria a 

 strain is occasionally found which will not grow on the gentian violet 

 media, differing in this respect from other members of the same species. 

 They find also that the reaction is quantitative. 



The streptococcus-pneumococcus group, according to their investi- 

 gations, differs from other bacteria in being able to grow in the presence 

 of quantities of violet which inhibit other Gram-positive species. Dys- 

 entery bacilli show variations. Other dyes which they investigated 

 showed no specific inhibitory properties which could be utilized for 

 classification. 



' Churchman, Jour. Exp. Med., 16, 1912; also Churchman and Michael, ibid. 

 ■' Signcrrelli, Centralbl. f . Bakt., Orig. 66, 1912. 



'Krumwiede and Pratt, Centralbl. f. Bakt., Orig. 68, 1913; and Proc. N. Y. 

 Path. Soc, xiii, 1913. 



