New study shows that E. coli can evolve antibiotic resistance during treatment

Scientists have documented a notable case of antibiotic resistance evolving within a critically ill patient during treatment for an E. coli bloodstream infection, providing genomic evidence of how drug resistance can emerge in real time.

This new study, led by Liverpool School of Tropical Medicine (LSTM) and published in the Journal of Medical Microbiology, details the rapid evolution of resistance in an E. coli strain exposed to piperacillin/tazobactam (TZP), a first-line treatment for serious bacterial infections that pairs an antibiotic with a compound that inhibits beta-lactamase enzymes, a widespread antibiotic resistance gene.

While the initial infection appeared treatable, the bacteria quickly developed a mechanism to escape the drug's effects, not by acquiring new resistance genes, but by amplifying one it already carried, overcoming the effects of the resistance inhibitor.

Dr. Thomas Edwards, a researcher within the LSTM Center for Drugs and Diagnostics and co-senior author of the study, said, "This is a striking example of resistance evolving under antibiotic pressure.

"We identified a tenfold increase in copies of a key resistance gene within the bacterial isolate, leading to a 32-fold increase in the level of antibiotic required to kill the bacteria, ultimately causing the treatment to fail, and all within the course of a single patient's illness."

Image source: Fraser et al. (2025), Journal of Medical Microbiology.