News in Science

Zombie bacteria may help heal wounds

Silver bullets Bacteria killed with silver can destroy living bacterial strains through a novel mechanism dubbed 'the zombie effect', a new study has found.

In the study, strains of Pseudomonas aeruginosa were killed with silver nitrate solution, a common antibacterial agent.

The bacterial cadavers were isolated, cleaned through and exposed to fresh, live Pseudomonas strains.

Exposure to nitrate solution didn't simply kill the bacteria, it actually turned them into long-lasting, silver-releasing 'zombie' bacterial killers.

"If an antibacterial agent remains chemically active after the killing action, then this is not the end of the story, but only the beginning of it", says the study's lead author Dr David Avnir of the Hebrew University of Jerusalem, in Israel.

"In principle, if not washed away, the same amount of agent can kill generation after generation," says Avnir.

The study, published in the journal Scientific Reports , is the first to report this novel antibacterial mechanism and has potential implications in the way wounds are treated, says Avnir.

"[The new mechanism] offers an explanation to the observation that in many cases the activity of antibacterial agents is prolonged, much beyond what one would expect from the administered dose."

He says the findings may lead to reduced doses of antibacterial medicines and reduce the toxicity effects in a range of applications that use metallic and non-biodegradable antibacterial agents such as the treatment of wounds and cleaning of circulated water.

Silver lining

A key aspect of antimicrobial agents concerns their long-term effectiveness, which is crucial in preventing bacterial re-colonisation.

In this sense, a major focus of recent research has been the development of an effective and long-term delivery system of antibacterial agents.

Some metals like copper and silver have been extensively studied for the antibacterial properties properties of their cations. The slow release of these positively charged atoms have been used to successfully prevent contamination of wounds, biomedical devices and textiles.

Avnir and his team set out to answer the long-standing question of what happens to silver after it kills the bacteria.

"From that question, and using some basic rules of chemistry, it became obvious to us that the silver which is contained in the dead bacteria, must be available to be released from the dead bacteria, and kill a new population of viable bacteria; it worked … beyond our expectations," he says.

Now Avnir seeks to apply his findings to other antibacterial agents and microorganisms.

"We intend to test how many cycles can a single dose can kill by forming generations of zombies," he says.

Related: Save silver for where it's needed