Despite 60 years of greedily guzzling penicillin, we have yet to doom our race to extinction at the hands of highly evolved superbacteria.
Scientists have known for some time that individuals within a species of bacteria can talk to each other via chemical signals. This allows a whole population to act in unison, as in the case of a coordinated attack on a host’s cells. According to recent research out of Princeton University, interfering with these signals may trick bacteria into feeling like they are alone, which could blunt their attacks. What’s more, since the approach does not rely on antibiotics, it wouldn’t encourage drug resistance.
In the September 29 issue of Nature, molecular biologists Karina Xavier and Bonnie Bassler report that many different species of bacteria share at least one chemical word. Since multiple species both produce and detect this chemical-known as autoinducer 2-one species of bacteria can interfere with the communication between members of another species by changing the amount of the chemical in a shared environment.
Scientists once thought that each species had an unique language of chemicals. Xavier asserts that this is still, basically, true: “This type of species-specific signal can be used by that species of bacteria as their private language because the other species cannot recognize the signal and cannot respond to it.”
But Xavier points out that there is a break in the code. “We believe autoinducer 2 can be used by the bacteria as common vernacular in a universal language,” she says.
Bassler says bacteria use a process called quorum sensing to detect the number of bacterial cells in a colony. When the level of a secreted chemical reaches a certain threshold, the entire population notices it simultaneously.
“Processes controlled by quorum sensing are those that, if a few bacteria did them, wouldn’t do much, but when the whole species does, it has amazing effects,” she says. “If one bacteria gets in you, the stupidest thing it can do is start secreting all of its toxins. Your immune system would get rid of it right away.” In the study, Xavier and Bassler cultured two kinds of bacteria together; both secrete autoinducer 2. One lit up when it detected a certain level of the chemical, the second responded to high levels of the chemical by removing it from the environment. Both bacteria reacted to the chemical, independent of which species produced it. The light-producer emitted light earlier than expected, indicating that both species were secreting autoinducer 2. The chemical-remover then removed the chemical earlier than expected, causing light production to shut off. Effectively, the chemical-remover species successfully made each member light-producer “think” it was alone.
Bassler said the human body may naturally capitalize on this ability to interfere with bacterial communication.
“We eat and drink gobs of bacteria all of the time and usually don’t get sick,” she says. “We wonder, why is that? And maybe it’s because there are all these shenanigans going on with quorum sensing.”
But sometimes we do get sick, and where the body fails to be manipulative enough on its own, scientists may be able to step in and fool the bacteria.
“Controlling bacterial behaviors by these types of processes that do not kill the bacteria is a good alternative to traditional antibiotics because non-killing therapies are less likely to cause the development of bacterial resistance,” Xavier says.
Originally published October 11, 2005
