Stress may protect-at least in bacteria
(PHYSorg.com Biology)

Antibiotics harm bacteria and stress them. Trimethoprim (TMP), an antibiotic, inhibits the growth of the bacterium Escherichia coli and induces a stress response. This response also protects the bacterium from subsequent deadly damage from acid. Antibiotics can therefore increase the survival chances of bacteria under certain conditions. This is shown in a study by researchers at the Institute of Science and Technology Austria (IST Austria), carried out by Karin Mitosch, Georg Rieckh and Tobias Bollenbach, which was published in the journal Cell Systems.