Antibacterial activity of silver-killed bacteria: the "zombies" effect

Racheli Ben-Knaz Wakshlak, Rami Pedahzur, David Avnir, Racheli Ben-Knaz Wakshlak, Rami Pedahzur, David Avnir

Abstract

We report a previously unrecognized mechanism for the prolonged action of biocidal agents, which we denote as the zombies effect: biocidally-killed bacteria are capable of killing living bacteria. The concept is demonstrated by first killing Pseudomonas aeruginosa PAO1 with silver nitrate and then challenging, with the dead bacteria, a viable culture of the same bacterium: Efficient antibacterial activity of the killed bacteria is observed. A mechanism is suggested in terms of the action of the dead bacteria as a reservoir of silver, which, due to Le-Chatelier's principle, is re-targeted to the living bacteria. Langmuirian behavior, as well as deviations from it, support the proposed mechanism.

Conflict of interest statement

The authors declare no competing financial interests.

Figures

Figure 1. Overview of the zombies effect…
Figure 1. Overview of the zombies effect experiment.
Figure created by R.B.-K.W.
Figure 2
Figure 2
Shown is the bactericidal effect of silver-treated P. aeruginosa cells towards fresh viable cells at increasing silver nitrate concentrations, after 6 h of exposure. Green: The antibacterial activities of the supernatant solutions of the initial kill. (Error range: ~10% of the log reduction values). Red: The antibacterial activity of killed bacteria.
Figure 3
Figure 3
TEM (bright background) and STEM (dark background) of P. aeruginosa before (a and d) and after (b, c and e) treatment with silver; the black (b) and white (e) granules represent silver deposition which account for the zombies biocidal action.
Figure 4
Figure 4
(a) Ag+ adsorption isotherm onto P. aeruginosa cells and its fit to Langmuir's equation. (b) The results of the more accurate Fireman-Shoresh et al analysis of the dependence of the adsorption equilibrium constant, K′, on coverage.

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