A new study from researchers in Germany found that caffeine from coffee and other sources can reduce the effectiveness of certain antibiotics against harmful bacteria.
Scientists at the Universities of Tübingen and Würzburg discovered that caffeine triggers a complex chain reaction in E. coli bacteria that makes them less susceptible to antibiotics like ciprofloxacin, a commonly prescribed fluoroquinolone used to treat urinary tract infections, pneumonia and many other bacterial infections.
The study was published in July in the journal PLOS Biology. It follows numerous other studies in recent years that have explored coffee’s relationship with medications as scientists seek to identify real-world implications.
“Caffeine triggers a cascade of events starting with the gene regulator Rob and culminating in the change of several transport proteins in E. coli — which in turn leads to a reduced uptake of antibiotics,” University of Tübingen professor Ana Rita Brochado said in an announcement of the study’s publication.
The researchers describe this phenomenon as an “antagonistic interaction” between caffeine and certain antibiotics.
The study examined how 94 different substances — including antibiotics, prescription drugs and common food ingredients — influence gene expression in E. coli, a bacterium that can cause serious infections in humans.
The researchers focused on transport proteins that act like gatekeepers, controlling what substances can enter or exit bacterial cells.
“Our data show that several substances can subtly but systematically influence gene regulation in bacteria,” said PhD student and lead author Christoph Binsfeld.
The work addresses “low-level” resistance — subtle, environmentally driven shifts that don’t rely on classic resistance genes but still change antibiotic susceptibility. For example, while caffeine itself isn’t an antibiotic, it may nudge bacterial regulators in ways that make some antibiotics less effective at entering the cell, according to the study.
The research revealed that about one-third of all tested compounds triggered previously unknown changes in bacterial gene activity. The effect was not detected in Salmonella enterica, a closely related species, underscoring that responses can differ across bacteria.
The research was supported by grants from multiple German funding agencies, including the German Research Foundation and the Bavarian State Ministry for Science and the Arts. The authors did not declare any competing interests.
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