Further Observations on the Differential Inhibition of Coliform Bacilli and Rough Variants of Intestinal Pathogens

Summary: The pattern of differential inhibition of Gram-negative bacilli of intestinal origin depends not only upon a synergy of bile salts and electrolytes of the Hofmeister series but also upon aerobiosis and the nature of the surface upon which they are grown (Brodie, 1948). Identical patterns of inhibition are obtained if shallow-layer fluid cultures are employed. The media under discussion possess lethal qualities which appear to be modified by a process akin to adsorption and the results obtained with solid media to depend in part upon the physical nature of the gel.

Electron microscope studies suggest that bile salts alter the permeability of the cell-wall, facilitating the entry of electrolytes. The resultant swelling or disruption of cells exposed to bile-salt + electrolyte mixtures and subsequently to distilled water is a measure of their electrolyte content. The ease with which organisms can be inhibited in the media seems to be directly related to their altered cell-wall permeability. The observations direct attention to physiological differences between rough and smooth variants of a single culture. They indicate that one factor upon which such differences depend is the greater permeability of the rough variant to electrolyte in the presence of bile salts.