BioEd Online

Little-known predatory bacteria can suck out the innards of bugs that cause lethal lung infections, microbiologists have shown, raising the hope that they might one day provide an alternative to conventional antibiotics.

Only a handful of researchers study bugs that prey on their neighbouring bacteria in soil and water. But a growing body of evidence shows that we might exploit these microscopic hunters to our advantage.

One type of predatory bug, called Micavibrio, feeds on other bacteria by latching onto them and siphoning out their contents. The bacterium was isolated over two decades ago, but has been largely ignored by scientists, partly because it is difficult to grow.

Horror film

Daniel Kadouri of Dartmouth Medical School in Hanover, New Hampshire and his colleagues have now found that Micavibrio can destroy sheets of Pseudomonas aeruginosa, a bug that can threaten the lives of patients with HIV, cancer and cystic fibrosis. These bacteria are difficult to attack because they form antibiotic-resistant sheets in the lungs called biofilms.

Kadouri found that Micavibrio can cut a population of P. aeruginosa biofilms tenfold, and that it killed 104 out of 120 strains isolated from patients. He presented the results at the American Society of Microbiology meeting in Orlando. "I think they do have therapeutic potential," Kadouri says.

But the bugs are a long way from the clinic, researchers say. We would need to be sure that the aggressive bacteria do not upset the balance of helpful bugs in the body, and that they do not provoke a dangerous immune response.

Mixed company

Research with another type of predatory bacterium called Bdellovibrio has shown some of the potential complications of using these bugs on patients.

Bdellovibrio bacteriovorus burrows into its bacterial prey and devours it from within. Between four and six new Bdellovibrio burst from the carcass, ready to attack new prey.

"They are fearsome predators," says Liz Sockett at the University of Nottingham, UK - but, she adds, "they are fab."

Researchers knew that Bdellovibrio can consume pathogenic bugs such as Escherichia coli and Salmonella. To see how they might perform in a real human wound, which teems with many types of bacterium, Sockett and her colleagues threw Bdellovibrio into a mixed population of E. coli and the common soil bacterium Bacillus subtilis.

Slowed slaughter

They found that the predator's slaughter of E. coli was slowed down. That's because the B. subtilis digested the dead E. coli and released compounds that fuelled new E. coli growth.

The experiments suggest that, should Bdellovibrio ever be used, doctors would need to adjust the dose to take other bugs into account, Sockett says.

Since Bdellovibrio was discovered in 1962, researchers have come to think that a host of unidentified predatory bacteria swarms around us. They hope that such bugs could be applied to wounds to consume infectious bacteria, or to keep medical devices or agricultural irrigation systems clean. Most researchers have found that bacteria do not become resistant to Bdellovibrio, perhaps because it attacks many different proteins on its prey rather than just one.

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