'Zombie' bacteria found able to kill other bacteria

May 4, 2015 by Bob Yirka, Phys.org report

Overview of the zombies effect experiment. Credit: Scientific Reports 5, Article number: 9555 doi:10.1038/srep09555
(Phys.org)—A trio of researchers with the Hebrew University of Jerusalem has found that bacteria that die as a result of silver poisoning can serve as a means to continue to kill other bacteria in the same environment. In their paper published in the journal Scientific Reports, the team describes how examination of dead bacteria revealed the silver that remained trapped inside of them and how it later caused the death of other bacteria.

People have been using to kill for thousands of years, but only in a direct way. In this latest effort, the researchers found that because poke holes in bacterial membranes and make their way inside, those that die serve as a sort of bank, holding onto silver reserves. But as time passes and the dead bacteria decay, the silver inside of them escapes into the environment around them, and if that environment has other bacteria in it, they are killed as well.

The team found this out by placing bacteria specimens in a solution containing bits of silver, then after the bacteria died, they pulled them from the solution and examined them under an electron microscope—they were able to see the bits of silver speckling the insides of an individual bacterium. Next, they put some dead individuals into a clean solution seeded with fresh bacteria and found that silver inside of it was released into the solution killing 99.99 percent of the bacteria—the team calls it the zombie effect. After their discovery they initiated several tests to determine the killing power of the solution polluted with the dead bacteria—they found that an initial low concentration was not enough to kill all of a third batch of bacteria, which indicated that the bacteria that had been killed by the remains of the first batch of bacteria, had soaked up by the silver—it was only after they decayed that the third batch was killed—thus it appears that the killing ability of the could conceivably carry on indefinitely as those that die, slowly release the silver inside them.

As the team explains, the bacteria are like sponges, soaking up silver, then releasing it after they die, causing it to be soaked up by other bacteria, and on and on. This, means, the researchers suggest, that methods of using silver as an antibacterial agent, might benefit from modification, allowing for an increase in longevity.

Explore further: Antimicrobials: Silver (and copper) bullets to kill bacteria

More information: Antibacterial activity of silver-killed bacteria: the "zombies" effect, Scientific Reports 5, Article number: 9555 DOI: 10.1038/srep09555

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.

Related Stories

Antimicrobials: Silver (and copper) bullets to kill bacteria

November 9, 2009

Dana Filoti of the University of New Hampshire will present thin films of silver and copper she has developed that can kill bacteria and may one day help to cut down on hospital infections. The antimicrobial properties of ...

Silver shines as antibacterial for medical implants

March 24, 2015

There have been growing concerns in the global health care system about the eradication of pathogens in hospitals and other patient-care environments. Overuse of antibiotics and antimicrobial agents has contributed to the ...

Spinning up antibacterial silver on glass

June 27, 2013

The antibacterial effects of silver are well established. Now, researchers at Yonsei University in Seoul, Republic of Korea, have developed a technique to coat glass with a layer of silver ions that can prevent growth of ...

Recommended for you

Coffee-based colloids for direct solar absorption

March 22, 2019

Solar energy is one of the most promising resources to help reduce fossil fuel consumption and mitigate greenhouse gas emissions to power a sustainable future. Devices presently in use to convert solar energy into thermal ...

NASA instruments image fireball over Bering Sea

March 22, 2019

On Dec. 18, 2018, a large "fireball—the term used for exceptionally bright meteors that are visible over a wide area—exploded about 16 miles (26 kilometers) above the Bering Sea. The explosion unleashed an estimated 173 ...


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.