The Gram Reaction and the Electric Charge of Bacteria

A number of investigators, particularly Winslow and his asso-ciates, have shown that bacteria carry a negative electric charge. The charge and consequently the rate of migration under the influence of an electric current can be modified by changes in pH. Stearns and Stearns (1924; 1925) have attempted to explain the Gram reaction of bacteria as related to or determined by the isoelectric point and the pH. Winslow and Upton (1926) failed to see any relation between the electric charge and the Gram reaction. The experiments described here were made to determine whether there exists any relation of this sort. EXPERIMENTAL A Gram-positive yeast and a Gram-negative bacillus, Escher-ichia communior, were used as the test organisms. These were grown on potato extract agar for 24 hours, scraped off with a loop and transferred directly to the desired pH solution. After shak-ing for 15 minutes to break up the clumps the suspension was centrifuged and the supernatant fluid poured off.-ivlore of the suspension fluid was added, shaking was continued for five min-utes and the pH adjusted to the desired point. The suspension fluid was made of distilled water adjusted to the approximate pH. After the organisms were suspended in it the pH was adjusted with the aid of the hydrogen electrode. The organisms were made up in suspensions ranging in pH from 1.0 to 14.0. The cell used for measuring the migration of the organisms was a modification of the apparatus described by Northrop (1922).