A large-scale genetic study has identified the five capsule types driving most multidrug-resistant bloodstream infections caused by E. coli. Researchers from the Wellcome Sanger Institute, University of Oslo, and collaborators examined over 18,000 bacterial genomes from samples worldwide to map this protective armor and explore ways to target it. Published in Nature Microbiology, the work identifies 90 capsule types, with only 34% previously known.
E. coli is the leading cause of bloodstream infections globally. While most strains reside harmlessly in the gut, some invade the bloodstream or urinary tract, causing mild to severe infections, especially in those with weakened immune systems. Antibiotic resistance complicates treatment, with over 40% of U.K. E. coli bloodstream infections resistant to a key antibiotic.
Protective capsules shield E. coli from the immune system and treatments, varying by strain with distinct antigens suitable for vaccine targets. Traditional capsule mapping proved labor-intensive, so the team created a digital database from 18,000 genetically analyzed samples, including nearly 8,000 from people aged from newborns to over 80.
This effort uncovered far greater diversity than expected—90 types total, including 69 new ones. Capsule prevalence differs by region: high-resource areas like the U.K.. show distinct patterns compared to Malawi and Pakistan. Five types (K1, K5, K52, K2, K14) drive over 50% of U.K., Norway, and France bloodstream and urinary tract infections. A related set (K1, K5, K52, K2, K100) accounts for 70% of multidrug-resistant cases in Europe. K1 and K5 appear globally, but low- and middle-income countries exhibit more strain variety in serious infections.
The study also shows E. coli swaps capsule-encoding genes across strains, adapting its armor. This blueprint aids targeted vaccines and treatments against dangerous strains, sparing beneficial gut bacteria. Global data proves essential, as capsule types vary by location.
Dr Rebecca Gladstone, first and corresponding author at the University of Oslo, said: "By creating a digital library from over 18,000 bacterial genomes, we can see the true complexity of how E. coli protects itself, and how this armor is encoded in the genes. This research has expanded our scientific map from just a handful of known bacterial shields to a comprehensive database of 90 unique types, including nearly two-thirds that were previously unknown. Ultimately, this database provides the missing blueprint to identify strains most likely to cause serious infections, and design targeted vaccines and treatments to stop these."
Publication details: Gladstone, R.A., Pesonen, M., Pöntinen, A.K. et al. Identification of transporter-dependent capsular loci associated with the invasive potential of Escherichia coli. Nat Microbiol (2026). https://doi.org/10.1038/s41564-026-02283-w
E. coli is the leading cause of bloodstream infections globally. While most strains reside harmlessly in the gut, some invade the bloodstream or urinary tract, causing mild to severe infections, especially in those with weakened immune systems. Antibiotic resistance complicates treatment, with over 40% of U.K. E. coli bloodstream infections resistant to a key antibiotic.
Protective capsules shield E. coli from the immune system and treatments, varying by strain with distinct antigens suitable for vaccine targets. Traditional capsule mapping proved labor-intensive, so the team created a digital database from 18,000 genetically analyzed samples, including nearly 8,000 from people aged from newborns to over 80.
This effort uncovered far greater diversity than expected—90 types total, including 69 new ones. Capsule prevalence differs by region: high-resource areas like the U.K.. show distinct patterns compared to Malawi and Pakistan. Five types (K1, K5, K52, K2, K14) drive over 50% of U.K., Norway, and France bloodstream and urinary tract infections. A related set (K1, K5, K52, K2, K100) accounts for 70% of multidrug-resistant cases in Europe. K1 and K5 appear globally, but low- and middle-income countries exhibit more strain variety in serious infections.
The study also shows E. coli swaps capsule-encoding genes across strains, adapting its armor. This blueprint aids targeted vaccines and treatments against dangerous strains, sparing beneficial gut bacteria. Global data proves essential, as capsule types vary by location.
Dr Rebecca Gladstone, first and corresponding author at the University of Oslo, said: "By creating a digital library from over 18,000 bacterial genomes, we can see the true complexity of how E. coli protects itself, and how this armor is encoded in the genes. This research has expanded our scientific map from just a handful of known bacterial shields to a comprehensive database of 90 unique types, including nearly two-thirds that were previously unknown. Ultimately, this database provides the missing blueprint to identify strains most likely to cause serious infections, and design targeted vaccines and treatments to stop these."
Publication details: Gladstone, R.A., Pesonen, M., Pöntinen, A.K. et al. Identification of transporter-dependent capsular loci associated with the invasive potential of Escherichia coli. Nat Microbiol (2026). https://doi.org/10.1038/s41564-026-02283-w