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K1 Capsule Genes Acquired Multiple Times in E. Coli Lineages, Study Finds

The polysaccharide capsule enclosing Escherichia coli dubbed K1 emerged independently in four different bacterial lineages, a new study has found. E. coli harboring the K1 capsule have been linked to severe disease, including bloodstream infections and meningitis that can have high mortality rates. With a combination of whole-genome sequencing, bioinformatics, and other tools, an international team of researchers examined more than 5,000 clinical E. coli isolates from six countries dating back to as early as 1932. As they report in Nature Communications, the researchers traced the origin of the K1 capsule, finding that it emerged independently in four different extraintestinal pathogenic E. coli phylogroups in the last 500 years — earlier than expected. "It was exciting to discover the possibility of reconstructing the evolutionary history of the K1 capsule over the last half millennium, and to see how the capsule genes have been acquired over and over again by many different lineages of this pathogen species over the centuries," first author Sergio Arredondo-Alonso from the University of Oslo and the Wellcome Sanger Institute says in a statement. Further in vitro analyses suggested that therapeutically targeting the capsule could sensitize K1-harboring E. coli to the human innate immune response.