Infection, kill thyself

New wound dressings drive bacteria down a suicidal path

Scientists are turning harmful bacteria into agents of their own destruction. In an effort to create antibacterial wound dressings, a new material comes laden with microbial booby traps that are triggered by the activity of harmful bacteria, scientists report online April 20 in the Journal of the American Chemical Society.

BETTER BAND-AIDS Future wound dressings might contain tiny vesicles that break down when exposed to bacterial toxins, releasing an antibiotic that then kills the attacking microbes and helps keep the wound safe from infection. Zhou et al./JACS 2010

Bacterial infections are a serious problem for patients with burns and other wounds, says study coauthor Toby Jenkins of the University of Bath in England. While many wound dressings today contain silver to thwart microbial activity, the metal can hurt human cells that are trying to regrow. The silver may also cull out weaker bacteria, leaving the survivors even more of a threat than before.

Jenkins and his colleagues have set out to build a better dressing by peppering it with tiny capsulelike vesicles that look to bacteria exactly like cells prime for infection. But when the bacteria do attack, they release an antibacterial agent that kills them and any of their kind that happen to be nearby.

The researchers tested their strategy by inoculating pieces of fabric with two harmful bacteria — a species of Staphylococcus and a member of the Pseudomonas group, famed for glomming onto medical devices — as well as a harmless type of E. coli.

When they placed the fabric scraps in petri dishes along with bacteria, the harmless E. coli grew readily. But the toxin-releasing Staph and Pseudomonas barely grew at all. This suggests that the harmful bacteria did in fact release toxins or enzymes that busted open the vesicles, unleashing the antibiotic inside and sealing their own fate. The E. coli flourished because they left the vesicles intact, the researchers suspect.

“This is a nice approach and they’ve shown in principle that it works,” says biomedical engineer Christopher Batich of the University of Florida in Gainesville. However, he cautions that the simple system has many hurdles to overcome before it will be useful in a hospital setting. For example, bacteria can’t be tidily arranged into “good” and “bad” groups where one is toxin-producing and the other is not. “You’d have to work with real bacteria and real wounds to see if it makes a difference,” Batich says.

For now, the team is trying to make vesicles that last longer than the current span of minutes to hours. And while the researchers tried their system with bacteria-killing sodium azide, in practice the vesicles would be filled with different antibiotics depending on the patient’s wound.

“I think it’s a lovely idea,” says microbiologist Simon Silver of the University of Illinois at Chicago, who was not involved with the work. But he wonders whether the technique would make much difference if bacteria were buried deep in a wound. “It’s too early to say if it will be more fruitful,” Silver says.

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