The electrical conductivity of bacteria, and the rate of sterilisation of bacteria by electric currents

Abstract

Electrical currents, both alternating and direct, retard the growth of bacteria in liquids through which they are passed, and under certain conditions cause complete sterilisation. The cell-contents are coagulated by the heat generated, or by electrolytic effects within or without the cell. There is the further possibility that protoplasm may be disintegrated by the mechanical action of an alternating current upon molecular charges, similar in effect to that of rapid vibration, which is known to check the growth of, and even to kill, bacteria. Whether the retardation of growth is regarded as the result of changes in the cell or liquid, the effect is largely controlled by the relation between their electrical conductivities. When these are the same the current flows as if the cell were not present, otherwise the current-density in the bacteria is greater or less than that in the liquid, according as their conductivity is respectively the greater or less. In order, therefore, to control effectively the bactericidal action of electrical currents in a liquid, the relative conductivities of the liquid and the contained bacteria should be known. A full summary of the industrial applications of electrical currents in organic processes is contained in Lafar’s ‘Technisches Handbuch der Mykologie.’ In most of the cases referred to the currents were weak and the voltage gradients in the liquid low. The special feature of the present work is that the voltage and current were taken to their highest limit, under the condition that the temperature did not exceed 30° C., with the testing cell cooled by immersion in running water. The ‘Comptes Rendus’ of April, 1896, contained a short account of observations by S. Lortet on the orientation of bacteria in water through which an alternating current was passed. It was stated that only living bacteria orientated, an observation which, if it had been confirmed, would have had bearing on the relation between electricity and life. This is, however, not the case, for bacteria which have been boiled for several hours orientate more freely than before. Lortet’s observations would be at once explained if his emulsion had been sterilised by the addition of an ionising liquid, such as perchloride of mercury, the conductivity of which is greater than that of the germs. The fact is that dead or living bacteria orientate equally well.

Bacterial Flagellum versus Carbon Nanotube: A Review Article on the Potential of Bacterial Flagellum as a Sustainable and Green Substance for the Synthesis of Nanotubes

“…(Cylindrical and hollow) hexagonal lattice helicity Nanotubes: ropes, tubes arranged in triangular lattice with lattice parameters of a ≈ 1.7 nm and tube-tube distance ≈ 0.314 nm (for DWCNTs and MWCNTs) [25,82] Elastic Modulus 1010 N/m 2~1 TPa~800 GPa~0.3-1 TPa [82,93] Tensile strength 3.5 pN/µm 2 (Pa) 50-500 GPa~30 GPa 10-50 GPa [82,94,95] Electrical Conductivity 35-350 ohms/cm 3 (bacteria) 10 6 to 10 7 S/m [96,97]…”

The present status of the pasteurization of milk /

“…Thornton (57), who studied this question in England, came to the conclusion that the killing of bacteria must be regarded as due largely to thermal rather than to electrical changes, but thought his results indicated some electrical action on the molecular structure of the bacteria. Beattie (9,10), also working in England on the same problem, came to the conclusion that heat was not the principal factor in killing bacteria by electricity, but found that to obtain satisfactory results the temperature should not be below 145°F.…”