Everyday substances, including caffeine, can trigger changes in bacteria like E. coli that make antibiotics less effective.
Caffeine activates a regulatory path involving a bacterial protein called Rob, leading to less “porin” channels, which antibiotics use to enter the cell.
The weakening effect depends on the antibiotic, the bacterial species, and specific genes; in Salmonella, for example, caffeine didn’t reduce antibiotic effectiveness the same way.
We all know caffeine wakes us up, but what if that same caffeine could interfere with antibiotics we need?
A new study from researchers in Germany has found that caffeine (and other common chemicals) can affect how bacteria respond to certain antibiotics.
The kicker: it’s not because caffeine kills bacteria or is antibacterial itself, but because it alters the way bacteria regulate what they let in and push out. In some cases, that can make antibiotics less able to do their job.
“Our data show that several substances can subtly but systematically influence gene regulation in bacteria,” researcher Christoph Binsfeld, said in a news release.
The study
To figure out how everyday substances might change the way bacteria react to antibiotics, researchers ran a kind of “stress test” on E. coli, a common gut bacterium.
They exposed the bacteria to 94 different chemicals — including antibiotics, prescription drugs, and food-related compounds like caffeine — and watched how the bacteria responded.
Instead of just looking to see whether the bacteria grew or died, the team zoomed in on the “gates” and “pumps” in the bacterial cell wall. These are the entry and exit points that antibiotics use to get inside or get pushed back out. By using a glowing marker system, the scientists could track whether these gates opened wider, closed tighter, or stayed the same when exposed to each chemical.
They also tested slightly altered versions of E. coli that were missing certain control switches. This helped them pin down exactly which internal regulators were responsible for the bacteria’s reactions.
The results
Caffeine stood out as one of the surprising players. On its own, caffeine didn’t harm the bacteria. But when it was present, it flipped on a genetic “switch” that told the bacteria to close some of its entry gates — specifically a channel called OmpF, which many antibiotics rely on to slip inside.
With fewer gates open, antibiotics like amoxicillin and ciprofloxacin couldn’t get in as easily. That meant it took higher doses of those antibiotics to slow the bacteria down. In fact, in some tests, E. coli became up to 40% harder to stop when caffeine was added.
The effect wasn’t universal, though. It depended on the specific bacteria and the drug. For instance, when the same tests were run on Salmonella, caffeine didn’t have the same impact. This shows that caffeine isn’t automatically a problem with all antibiotics, but it highlights how even common, everyday substances can sometimes tip the balance in bacteria’s favor.
“Such fundamental research into the effect of substances consumed on a daily basis underscores the vital role of science in understanding and resolving real-world problems,” President Prof. Dr. Dr. h.c. (Dōshisha) Karla Pollmann said in the news release.