The communal activity of bacteria

Abstract

It has been shown above that, while B. coli like—most of the gram negative organisms—is apparently uninfluenced in growth by gentian violet, a careful study of thick suspension will demonstrate the presence of many individuals which are susceptible to the dye.

The isolation of a strain of B. coli entirely fast to gentian violet—that is to say, containing no individuals susceptible to the bacteriostatic effects of the dye—has made it possible to study quantitatively the reaction between this bacteriostatic agent and bacteria, without encountering the disturbing factor usually met in such studies and caused by the variability of the susceptibility of the individual organisms to the chemical substance under examination. This strain of B. coli had been isolated from a single colony growing on gentian violet agar and had been kept growing on gentian violet agar by frequent transplants over a period of several weeks. Every individual had therefore proven its ability to grow in the presence of the dye by actually having done so.

Working with such a culture it is found that, though large inoculations of gentian violet media produce as heavy growths as in plain media and that the dye therefore seems to have no inhibitory effect, single cell transplantations (by the method of Barbour) never grow. Nor does growth occur if small groups (under 30) are transplanted. This would indicate that bacteria do not, as is commonly supposed, act as isolated individuals; they possess the power, in numbers, of accomplishing effects which, alone, they are incapable of. The nature of this community of action it is at present impossible even to guess at.