"These bacteria are able to penetrate the double membrane of Gram-negative bacteria, enter into the prey and consume it from the inside out," says Mitchell. After sucking down a tasty meal, the BALOS use the energy boost to multiply. "A predator can produce anything from two to seven progeny from a single prey.
Scientists don't know enough about predatory bacteria to "program" the hungry suckers to target specific microbes. The best current technique, Mitchell explains, is to identify naturally occurring predators that have a "taste" for certain kinds of diseases. Once the predator bacteria are isolated in culture, researchers must feed them daily to keep them alive and reproducing. Then it's time to set them loose on disease pathogens.
Kadouri's rat experiments were the first ever to employ therapeutic predatory bacteria in living mammals. Before that it was just fish and chickens. The dream is to one day test these disease-hunting bacteria in humans. Earlier this year, both Mitchell and Kadouri proved in separate studies that BALOS pose no threat to healthy human cells in culture. Testing on real people is still years away.
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"One of the biggest obstacles to human trials, other than federal approval, is psychological," says Mitchell, "It's the whole idea of telling a patient, 'Hey, we're going to get rid of your pathogenic bacteria by feeding you bacteria.'"
Another big unknown is the long-term effect of these predatory bacteria inside the body. Will they establish themselves and become part of the body's microbial mix? And is that a bad thing or a good thing? Mitchell and his colleagues are chasing down these answers, thanks in part to grants from DARPA's Pathogen Predators program.
In the meantime, the global health community is on high alert. In September, the United Nations held its first-ever general assembly dedicated exclusively to antimicrobial resistance. Addressing the assembly, the World Health Organization's director general, Margaret Chan, warned that a lack of new treatment options could soon give rise to a terrifying post-antibiotic era.
"Doctors facing patients will have to say, 'I'm sorry - there's nothing I can do for you.'"