A disease-causing bacterium 'eavesdrops' on another, usually harmless, bacterial species to help it survive antibiotics. Under certain conditions, populations of Escherichia coll that live in the gut secrete indole, a signalling molecule that makes them more tolerant of antibiotics. Although the gut pathogen Salmonella typhimurium (pictured) cannot produce indole, it still responds to it. James Collins at Boston University, Massachusetts, and his colleagues showed that S. typhimurium exposed to indole or to indole-producing E. coli survived better under antibiotics than did bacteria in indole-free conditions. In both species, indole strongly boosted the expression of stress-response genes known to help bacteria withstand drugs and assaults by the human immune system. Such interactions between species could help harmful bacterial infections to persist, the authors say.
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