The study’s findings challenge the traditional view that people are generally infected by a single genetic clone (or ‘strain’) of pathogenic bacteria, and that resistance to antibiotic treatment evolves because of natural selection for new genetic mutations that occur during the infection. The results suggest that instead patients are commonly co-infected by multiple pathogen clones, with resistance emerging as a result of selection for pre-existing resistant clones, rather than new mutations.
Lead researcher Professor Craig Maclean, from the University of Oxford’s Department of Biology, said: ‘The key finding of this study is that resistance evolves rapidly in patients colonized by diverse Pseudomonas aeruginosa populations due to selection for pre-existing resistant strains. The rate at which resistance evolves in patients varies widely across pathogens, and we speculate that high levels of within-host diversity may explain why some pathogens, such as Pseudomonas, rapidly adapt to antibiotic treatment.’
The researchers used a novel approach which studied changes in the genetic diversity and antibiotic resistance of a pathogenic bacteria species (Pseudomonas aeruginosa) collected from patients before and after antibiotic treatment. The samples were isolated from 35 intensive care unit (ICU) patients in 12 European hospitals. Pseudomonas aeruginosa is an opportunistic pathogen that is an important cause of hospital-acquired infection, particularly in immunocompromised and critically ill patients, and is thought to cause more than 550,000 deaths globally each year.