A new research publicated the last week in Scientific Reports in Nature showed that when bacteria are exposed to a solution of silver, can absorbe the silver particles and die, after this dead-bacteria can kill a viable culture of the same bacterium.
The silver was used since 1893 as antimicrobial for Karl Wilhelm Von Nageli showed the silver's properties as the capacity for permeability of the membrane and once inside the cell, altering its enzymatic system, inhibiting its metabolism and energy production and modifying its genetic material, losing the ability to grow and replication, for this has been employed in the elimination of pathogenic microorganisms.
But the zombie effect has been recognized to now. This mechanism was show with Pseudomonas aeruginosa (viable bacterial population of ca. 108 CFU/ml) wich was killed when was added nitrate silver solution to different concentrations (1, 2, 5, 15 and 20 ppm) then, this tubes were centrifugated and filtrated and the supernatat was mixed with viable culture of the same bacteria (108 CFU/ml) for 6 hours, then were counted the viable cells.
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| P. aureginosa before to treatment with silver (Wakshlak et al., 2015). |
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| P. aeruginosa after to treatment with silver; the white granules represent silver deposition which account for the ‘‘zombies’’ biocidal action (Wakshlak et al., 2015). |
This is due to the dead-bacteria serve as reservoir of silver and the metallic cations are released which are lethal for the live bacteria, the explanation of this phenomenon is given by the principle of Le-Chatelier wich says that if in a equilibrium system is modificated some factor (pressure, temperature, concentration, ..) the system evolves in the direction that tends to oppose this modification. It is said that the equilibrium is shifted to the right (if increases products concentration and decreases the reactive to the initial equilibrium), or left (if increases the reactants concentration and the product concentration decrease).
In this experiment the principle was demonstrated when the silver cations were transferred to dead-bacteria and the viable bacteria because they acted as new unoccupied adsorption sites for silver, and the equilibrium of silver between the reservoir and the liquid, is shifted.
This investigation proposed a new biocidal agent for microbial infection when the silver concentration adequate is added. Although exist diverse factors involved that can be reviewed in future researches.
If you want to know more: Antibacterial activity of silver-killed bacteria: the "zombies" effect
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