The effect of neomycin and streptomycin on the electrical polarisability of aqueous suspensions of Escherichia coli.
Aqueous suspensions of bacteria scatter light strongly. In addition, the bacteria exhibit strong induced dipole moments in an electric field. In this note we report how, by measuring the intensity of the scattered light, the electric polarisability (alpha) of Escherichia coli could be monitored as small quantities of antibiotics were added to the suspensions. The effect of the presence of quite small quantities of antibiotic on the electrical polarisability, which gave rise to the induced dipole, was dramatic. From the hypothesis that alpha had its origins in the bacteria-solvent interface, a theory is presented which adequately accounts for both alpha and its changes in the presence of these antibiotics. The study is taken to suggest that the antibiotic molecules were adsorbed on to the bacterial surface thereby reducing the surface charge. This in turn reduces the number of counterions and the apparent induced dipole moment. Because the electric-field scattering method is both quick and sensitive to changes in alpha, it may prove a valuable method for the study of antibiotic action on  cell and microorganism surfaces.
D004926:Escherichia coli / Q000187:drug effects / Q000502:physiology*; D008027:Light; D008433:Mathematics; D009355:Neomycin / Q000494:pharmacology*; D011048:Polarography; D012542:Scattering, Radiation; D013307:Streptomycin / Q000494:pharmacology*
D009355:Neomycin; D013307:Streptomycin