In the war against "super bugs" like MRSA, scientists are finding that the way to defeat them and any other bacteria may be by disrupting their communication. As this ScienCentral News video explains, decoding the language of bacteria might lead to powerful new antibiotics.
Bacteria Chatter
In Bonnie Bassler's lab at Princeton University, researchers use bioluminescence to reveal when bacteria are talking to each other and what they're saying. It's only recently that scientists have discovered that bacteria communicate with each other at all. "We've known about bacteria for over 300 years and they've always been considered these asocial, reclusive organisms," says Bassler. But her research is helping to reveal their hidden chemical language.
One important topic for bacteria "discussions" is attendance at the party. When bacteria infect a host and begin to replicate, they send out two chemicals: one chemical that is specific to its species and another that is a kind of universal beacon. The bacteria in the group measure the relative concentration of these molecules. The process is called quorum sensing. "It tells them 'I'm in the minority' or 'I'm in the majority'," explains Bassler, "and then they do different things based on whether they're winning, you know, or they're losing. Just like you or I would if we're in like a hostile group versus a friendly group."
Many harmful bacteria follow this pattern of infection: they enter our body through an open wound or via contaminated food or water, they replicate and adhere to tissues in the body, and then when they've created a viable attack force, they signal each other to turn on virulence and damage the host. Bassler explains her strategy, "We want to make molecules that jam the receptors, that make the bacteria unable to 'talk,' or unable to 'hear.'"
They wrote in the journal Nature their first target was the bacterium that causes cholera, a life-threatening diarrheal disease people get by driking unsafe drinking water or food. Cholera is rare in the U.S., but regions with inadequate clean water throughout the world see hundreds of thousands of cases of the disease a year.
Microscopic image of cholera bacteria image courtesy Centers for Disease Control
Cholera behaves differently than most other disease bacteria that have been studied. When cholera infects the body, it immediately becomes virulent, releasing toxins that make people sick. Once it detects–using quorum sensing–that it has reached a critical mass, the bacteria signal each other to turn off virulence and exit the body to infect other people. Bassler says, "Cholera provided this unique opportunity because if we could just get the real [signaling] molecule, we could add it, and the bacteria should become non-pathogenic. And so that's what we did."
A Different Kind of Antibiotic
All antibiotics developed in the past 50 years, explains Bassler, "work by exploiting some property of the bacterium that kills them; [for example] they pop their membranes, they make it so their DNA can't replicate. So traditional antibiotics kill bacteria." Bacteria that are vulnerable to the antibiotic drug die, but those that have a natural resistance survive and thrive. The result can be drug-resistant diseases like MRSA and MDR Tuberculosis.
But Bassler says their technique could be used to one day develop new types of antibiotics. And since interfering with their communication doesn't actually kill bacteria, researchers hope such drugs won't promote resistance as strongly as current antibiotics do.
She says there's also interest in industrial applications of signaling or interfering molecules that affect quorum sensing. The molecules could be put on plastic wrap at the deli to reduce the risk of E. coli infection, in toothpaste to prevent that film you get on your teeth overnight, and on catheters at the hospital to reduce the risk of infection. They could even be put in paints for cooling towers that tend to get bacterial build-up.
But Bassler insists bacteria shouldn't just be seen as the enemy. Bacteria live all over and inside us, and most of them are friendly. "We're not alive without the bacteria that are in us and on us. They're fending off invaders, they're playing an active role in keeping us healthy. We'd also like to make molecules that help the beneficial bacteria, and I think that's an equally viable strategy."
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