A woman got a UTI. Two years later, the bacteria had evolved, invaded her brain.
A 63-year-old woman suddenly lost sight in her right eye and was found to have inflammation there alongside brain lesions caused by a bacterial abscess. Tests linked the infection to Klebsiella pneumoniae first detected in her urine, illustrating how bacteria can evolve within a patient into forms capable of spreading through the bloodstream and damaging distant organs.
Doctors found that later urine and brain samples contained a sticky, capsule-rich, hypervirulent form of the bacterium, unlike an earlier ordinary-looking urine sample. Genome sequencing showed the samples were closely related but had acquired mutations affecting capsule production; the altered bacteria resisted immune cells and proved lethal in mice, although they grew more slowly and infected bladder cells less effectively.
In short
- UTI bacteria evolved into a brain-invading, hypervirulent form.
- The infection caused vision loss and a brain abscess.
- Mutations produced a protective sticky bacterial capsule.
Explained simply
A urinary tract infection, or UTI, is a common bacterial infection of the bladder and urine system, usually treatable with antibiotics. In this case, a bacterium from a routine UTI evolved over two years into a much more dangerous form that spread beyond the urinary tract to the brain.
The bacterium mutated, developing a thicker outer coating that made it harder for the body's immune system and antibiotics to fight it. These changes allowed the bacteria to escape the urinary tract, enter the bloodstream, and eventually reach the brain, where it caused a serious infection that damaged eyesight.
The case illustrates that bacteria can adapt and change whilst living inside a patient, becoming more harmful over time. Scientists studying how bacteria evolve in this way can understand why certain infections become harder to treat and what makes some bacterial forms more dangerous than others.