The ability to test the susceptibility of bacteria to antibiotics is recognized as one of the most important factor for deciding which antibiotics to prescribe. Surprisingly, all the current tests are detect only the ability of antibiotics to prevent the growth of bacteria, without being able to determine whether the antibiotic actually kills the pathogen. We have developed a low cost antibiotic susceptibility test that can evaluate whether an antibiotic only arrests the growth or kills the bacteria. Using this survival assay on clinical isolates, we were able to detect tolerant strains, i.e. strains that are killed significantly less efficiently without being resistant. These strains were also associated with a higher rate of reinfection in patients. Furthermore, our test enabled us to find combinations of antibiotics that could restore the killing efficacy of treatment in tolerant strains. We expect our results to pave the way for devising better treatments for treating persistent infections in hospitalized patients.
