Quantitative relationships of specific adsorption of colicins

The decrease in the number of sensitive bacteria in the presence of an excess of colicin is proportionate to their initial concentration; the proportion of surviving cells is not entirely constant, but is to some extent directly correlated to the initial cell concentration. The percentage of surviving cells is in inverse proportion to the colicin titre. The amount of nonadsorbed colicin is directly proportionate to the initial colicin titre. In the presence of an excessive number of sensitive bacteria in the suspension, the free colicin titre is much more lowered than in the suspension of resistant bacteria, the decrease being directly correlated to the number of bacteria in the suspension. Resistant—and even heterologous— bacteria can also adsorb large amounts of colicin nonspecifically, however. The experiments provide evidence in support of the concept of the lethal unit of colicin the course of adsorption of which is apparently different from that of phage.