COLON-TYPHOID BACTERIA 99 



of the zone depending upon the moisture content of the medium, the 

 degree of diffusion of the active substance, its concentration, and the 

 resistance of the test bacteria. When either of the two pathogens was 

 inoculated into liquid media and the antagonist was introduced simul- 

 taneously or within 24 hours, the latter had a decided bactericidal effect. 



No less extensive is the literature on the antagonistic action of the 

 fluorescent group of bacteria, first established by Garre (315) in 1887 

 and later by others. Its bacteriostatic spectrum is illustrated in Table 

 14. The active substance is thermostable, dialyzes through a membrane, 

 passes through Seitz and Berkfeld filters and is said to be soluble in 

 chloroform (418, 566). Aerobic culture conditions are favorable to its 

 accumulation. Members of this chromogenic group of bacteria were also 

 found to be able to bring about the lysis of infusoria (134). 



S. marcescens exerts antagonistic effects against a number of bacteria, 

 including diphtheria, gonococci, anthrax, and CI. chauvoeiy as well as 

 fungi causing insect diseases (624). The formation of antibiotic sub- 

 stances by this organism has been demonstrated by various investi- 

 gators. These substances are active not only in vitro but also in vivo. 

 Their formation was believed not to be associated with the production 

 of the pigment by the organism. Hettche (420), however, asserted that 

 the bactericidal action of Serratia is closely related to pigment produc- 

 tion. The pigment was extracted with alcohol and was found capable of 

 dissolving dead gram-positive bacteria but not gram-negative organ- 

 isms. Eisler and Jacobsohn (229) ascribed the antagonistic action of 

 Serratia not to the pigment but to certain water-soluble, thermostable 

 (70° C. for 30 minutes) lytic substances. 



THE COLON-TYPHOID BACTERIA 



Members of the colon-typhoid group are not typical soil inhabitants, 

 although they find their way continuously into the soil and into water 

 basins. Various organisms belonging to this group have been said to 

 possess antagonistic properties (440). Bienstock {ss) reported, in 

 1899, that proteolytic bacteria are repressed by the presence of E. coli 

 and A. aero genes. Tissier and Martelly (912) emphasized that this 

 phenomenon occurs only in the presence of sugar, the effect being due 



