Klebsiella pneumoniae, the bacteria behind many common urinary tract infections, can evolve into a more dangerous strain that spreads to the brain and causes life-threatening abscesses, scientists have warned in a new case report from Germany.
The bacteria normally lives harmlessly in the intestines but can cause infection if it spreads to the urinary tract, blood or wounds. In serious cases it can trigger sepsis or necrotizing fasciitis, a condition where tissue turns black and dies.
Researchers at a hospital in Cologne reported that a 63-year-old woman was admitted to their unit with a urinary tract infection and sudden vision loss in her right eye. Scans showed eye inflammation and lesions in her brain, particularly on the parietal lobe, which processes sensory information.
Doctors took two urine samples and a sample from inside her skull. All three tested positive for Klebsiella pneumoniae, and two of them carried an evolved strain coated in a slime capsule that researchers said helped it dodge the immune system and multiply in the body.
The infection was cleared quickly with antibiotics. Researchers suggested the more virulent bacteria may have evolved in the patient over one to two years, noting she had been treated for another urinary tract infection two years earlier.
How the bacteria evolves
Researchers explained that a subpopulation of bacteria, a genetically distinct group within a larger population, can emerge in an infection when some bacteria become better at spreading in the body or resisting antibiotics.
Dr Christoph Ernst, the microbiologist who led the research, said the findings show that highly virulent bacteria can evolve within an apparently harmless reservoir such as a urinary tract infection. He said the team suspects such virulent populations are especially prevalent in multidrug-resistant infections.
It was not clear whether the evolution of the bacteria caused the brain infection, since brain infections from this bacteria are reported only rarely, but the evolved strain was better able to evade the immune system, raising the likelihood it could infect other organs. There is no evidence the bacteria spread from the woman to other people.
It also remains unclear how the bacteria reached her brain. One theory is that the eye served as an entry point after the bacteria was transferred there by a contaminated hand.
A new phenomenon
Researchers described the case as an example of a phenomenon they called heterovirulence, in which a new, more virulent strain emerges that is outcompeted by the main strain in one area, such as the urinary tract, but is better able to spread and infect other areas, such as the eye.
The case report was published in the New England Journal of Medicine.
Who is most at risk
About eight million urinary tract infections are recorded in the United States every year, and at least a million of those are thought to be caused by this bacteria. People with a weakened immune system, diabetes or a recent surgery face a higher risk of infection.
Women are far more likely than men to suffer a urinary tract infection, which researchers say is because their urethra is shorter and closer to the anus. The bacteria is a particular problem in hospitals, where it can linger on surfaces and spread between sick patients, transmitted by touching a contaminated surface and then another body part, or through contaminated medical devices.
Warning signs of infection include difficulty urinating or painful urination, pain in the urinary tract, and fever and chills. Anyone who suspects they have the infection is advised to consult their doctor, since it is normally treated with antibiotics.
