Effect of a quaternary ammonium germicide on electrophoretic mobility of Escherichia coli in various salt solutions.

Quaternary ammonium compounds, effective as sanitizing agents for food plant equipment under certain conditions, are not well suited as sanitizers for water of high mineral content. Mueller and Seeley (1951) have demonstrated under controlled conditions that various metallic cations can decrease the germicidal action of a quaternary in solution. Knowledge of how such interference takes place could aid in overcoming this limitation. It might also permit the use of metallic cations as inhibitors in germicidal tests that require complete inactivation of the germicide after a given time. The purpose of this study was to find an explanation for the interference of metallic cations with the germicidal properties of quaternary ammonium compounds. The hypothesis that the metallic cation could inactivate the quaternary by association to form some type of chemical complex was investigated in preliminary experiments. Results obtained indicated that such a chemical complex was not formed. This result was expected in the light of the molecular structure of the quaternary. An explanation of the interference of metallic cations with quaternaries could be that metallic cations are attracted more readily than quaternaries to the electronegative surfaces of bacteria. These metallic cations, smaller and more mobile than quaternaries, should be preferentially adsorbed at the bacterial surface. Their presence would decrease the over-all electronegativity of the surface, thus lessening the electrostatic attraction between quaternary and surface. The technic of microelectrophoresis was used to explore this possibility. Electrophoresis is the directed movement of a particle under an applied potential. The velocity of movement, under controlled external conditions, is directly proportional to the electrical charge on the particle. Thus, measuring electrophoretic mobilities of bacteria when external conditions, such as the suspending medium, are varied would'indicate the effect of these conditions on the surface charge of the bacteria. A series of experiments was drawn up to observe the electrophoretic mobility of bacteria in the