Explaining how cooperative individuals positively assort into a cohesive community is one of the greatest challenges for evolutionary biology. Here, we show that in antibiotic culture, many and even all of Escherichia coli bacteria cells will plastically mutate to be antibiotic resistant with the increase of antibiotic concentration and then altruistically protect antibiotic-sensitive individuals from the attack of antibiotics. A further experiment showed that antibiotic-sensitive E. coli strain could in turn help reduce the indole produced by the resistant strain;whistthis metabolic product is harmful to the growth of the antibiotic-resistant strain but benefits the antibiotic-sensitive strain by helping turn on the multi-drug exporter to discharge the antibiotic. A reciprocal cooperation can therefore evolve via a non-positive exchange between the metabolism byproduct indole of antibiotic-resistant cells and the indole-aborting service of antibiotic sensitive cells as unconscious help in nullifying indole side effect of antibiotic resistant strain.