Molecular epidemiology and structural diversity of O101/O162 O-antigen variants among Escherichia coli bacteremia isolates

Most human invasive infections caused by extraintestinal pathogenic Escherichia coli (ExPEC) are associated with a limited number of O-serotypes and O-serogroups, including O101/O162. Here, we examined E. coli O101/O162 O-serogroup epidemiology among bacteremia isolates and performed genetic, biochemical and structural analyses. We demonstrate that the O101/O162 O-serogroup is globally widespread and highly associated with multidrug resistance (MDR). Dominant lineages belonged to clonal complex 10, including the high-risk clone ST167. Most O101/O162 ExPEC isolates contained an unusual O101 rfb locus previously identified as Onovel32, of which 30% harbored disruptions in the methyltransferase (MT) encoding gene. These disruptions resulted in alteration of the polysaccharide composition, and we identified two major O101 variants. Additionally, we found that an intact MT is a prerequisite for O-methylation of the polysaccharide, indicating terminal capping. Our data supports a model of a co-polymeric O101 O-antigen structure, which is unique for E. coli. Finally, we established that the two clinically relevant O101 O-antigen variant structures are highly immunogenic as polysaccharide-protein conjugates but differ in their ability to elicit opsonophagocytic antibodies. Altogether, our data provides important insights into O-serotype epidemiology and O-polysaccharide variation within E. coli O101/O162 isolates associated with bacteremia.