Silver, platinum, gold, stainless-steel, and copper electrodes were used with low currents (0.02 to 20'gA/mm2) to explore their electrochemical effects on the growth of four bacterial species. In the higher current ranges, all electrodes inhibited growth at both poles, usually in conjunction with electrolytic breakdown of the medium and severe corrosion of the metal. Silver, however, was extremely bacteriostatic, even at the lowest current, when used as the anode. Quantitative studies showed that most of this inhibition takes place in a few hours and is not accompanied by changes in pH. Electrochemically injected silver from the anode is probably the instrumental agent, being effective in conc,entrations of about 5 lAg/ml. This is the equivalent concentration of silver sulfadiazine that has been shown to give complete inhibition of bacteria, but without the sulfonamide moiety.The inhibition of bacterial multiplication by use of electric currents and metal electrodes has been reported (3,5,6,8). Whether alternating or direct currents were used, most authors agree that electrochemical products at the electrodes and/or metal ions are instrumental in this effect. In most cases, however, the currents were high enough to produce severe changes in the medium, especially near the electrodes.The present study was undertaken to explore the effects of relatively weak direct currents (and their electrochemical products) on agar plate bacterial cultures of Staphylococcus aureus, Escherichia coli, Proteus vulgaris, and Pseudomonas aeruginosa. Attention is paid to: (i) the electrode metal, (ii) the surface current density at the electrode, and (iii) the spatial character and polarity of the effects. We also report the results of more detailed measurements of viable organisms in the region of silver electrodes in liquid broth cultures as a function of time, current, and polarity.In a preliminary study (1) on S. aureus, it was found that currents of the order of 10-8 A/mm2 with silver electrodes can give rise to significant local inhibition. Much higher currents were required for platinum, gold, and stainless steel, usually in association with the breakdown of the electrolyte, to achieve similar effects. MATERIALS AND METHODSQualitative studies. Culture plates (45 mm) were prepared by mixing 0.5 ml of broth medium (GIBCO 1-t-1859) containing exponential-phase bacteria (optical density of 0.17 to 0.23 at 500 nm) with 3 ml of nutrient agar (GIBCO 1-t-1904) at 48 C. Identical electrode pairs (20 by 0.2 to 0.4 mm) were included in the plates and emerged through the sides. Pure silver (99.99%), platinum (99.9%), gold (99.99%), surgical stainless-steel (no. 316L), or copper (99.99%) wires were used. Battery-operated, constant-current generators (modifications of Vitron LIDC generators kindly supplied by Jack TerBeek of the Ritter Co., Rochester, N.Y.) were applied to the electrodes (except controls) after solidification of the agar and throughout incubation (37 C, 24 h). Current levels were 0.4, 4.0, 40, and 400 uA. In some cases the ...

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