Antibacterial Activity of Silver-killed Bacteria: the “Zombies” Effect
Most researchers agree that silver kills bacteria in a three-fold manner, i.e., catalytic oxidation, cell wall disruption and penetration leading to disabling of the bacterium’s respiration and energy transfer systems, and prevention of replication by attaching to the DNA of the pathogen. What happens afterwards is what researchers did not know until now.
In this clinical study from researchers at the Hebrew University of Jerusalem, published in the journal Scientific Reports in April 2015, it was discovered that the pathogens killed by silver then go on to kill other pathogens in the same colony. This is because as they die, they absorb more silver, like a sponge. This absorbed silver is then able to leach into the remainder of the bacterial colony, killing even more bacteria. In essence, the dead bacteria become “zombies,” spreading death throughout the rest of the colony thanks to their close proximity. In the preface to the study, the researchers state, “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.” In other words, when dead bacteria that were killed by silver are exposed to living bacteria, the living bacteria are in turn killed.
