New Test Measures How Effectively Antibiotics Kill Bacteria

Antibiotics are typically evaluated by how well they inhibit bacterial growth in laboratory tests, but growth inhibition does not always mean the bacteria are actually killed. Some pathogens can survive antibiotic exposure by entering a dormant state and later restart infection once treatment stops. This problem is especially serious in long and complex infections such as tuberculosis, where incomplete bacterial killing leads to relapse and treatment failure. Researchers have now developed a method that directly measures whether antibiotics eliminate bacteria at the single-cell level.

Researchers at the University of Basel (Basel, Switzerland) have developed a technique called antimicrobial single-cell testing to assess the killing efficiency of antibiotics rather than just their ability to inhibit growth. The method uses high-resolution microscopy to track millions of individual bacteria over several days under thousands of treatment conditions. By continuously filming each bacterium, the system determines whether cells die, survive, or recover after exposure, providing a precise measure of bacterial eradication across a population.

To validate the approach, the researchers tested 65 antibiotic combination therapies against Mycobacterium tuberculosis. They also applied the method to bacterial isolates from 400 patients with Mycobacterium abscessus lung infections. The results revealed substantial differences in killing efficiency between drug regimens and between bacterial strains from different patients. Genetic analysis showed that specific bacterial traits were linked to antibiotic tolerance, explaining why some infections persist despite treatment. The study, published in Nature Microbiology, showed strong agreement between single-cell testing results and outcomes seen in clinical studies and animal models.

The findings demonstrate that antibiotic tolerance, even without classic resistance, significantly reduces treatment success. Measuring how many bacteria actually die provides a clearer picture of whether a therapy can fully sterilize an infection. This approach could help clinicians select drug combinations that are more likely to cure difficult infections. Although currently used as a research tool, antimicrobial single-cell testing could eventually support personalized antibiotic selection in clinics and improve the evaluation of new antibiotics during drug development. Future work aims to simplify the method and translate it into faster diagnostic tools.

“The better bacteria tolerate an antibiotic, the lower the chances of therapeutic success are for the patients,” said Dr. Lucas Boeck, who led the study. “Last but not least, the data can help researchers to better understand the survival strategies of pathogens and thus lay the foundation for new, more effective therapeutic approaches.”

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