In a surprising discovery researchers at Boston University and the Wyss Institute for Biologically Inspired Engineering at Harvard have found that charitable behaviour exists in one of the most microscopic forms of life—bacteria. While studying the development of antibiotic-resistant strains of bacteria, they found that the populations most adept at withstanding doses of antibiotics are those in which a few highly resistant isolates sacrifice their own well being to improve the group’s overall chance of survival.

This bacterial altruism results when the most resistant isolates produce a small molecule called indole.

Indole acts as something of a steroid, helping the strain’s more vulnerable members bulk up enough to fight off the antibiotic onslaught. But while indole may save the group, its production takes a toll on the fitness level of the individual isolates that produce it.

“We weren’t expecting to find this. Typically, you would expect only the resistant strains to survive, with the susceptible ones dying off in the face of antibiotic stress. We were quite surprised to find the weak strains not only surviving, but thriving,” Nature quoted lead investigator Dr. James J. Collins, professor of Biomedical Engineering at Boston University and a core faculty member of the Wyss Institute, as saying.

The findings also shed new light on the level of complexity and heterogeneity within bacterial strains. Until now, it was assumed that the overall resistance level of any given population was reflected in each of its isolates. Instead, the researchers found that dramatic differences can exist within a single population with some bacteria showing exceptional resistance and some almost none, not unlike cancer cells in humans.

The fact that the full complexity of bacteria strains can now be more accurately understood has significant ramifications for the medical community. “Now, when we measure the resistance in a population, we’ll know that it may be tricking us. We’ll know that even an isolate that shows no resistance can put up a stronger battle against antibiotics thanks to its buddies,” said Dr. Collins. The findings appear in the latest issue of Nature.

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