LPS core type diversity in the Escherichia coli species and associations with phylogeny and virulence gene repertoire.

Escherichia coli is a very versatile species for which diversity has been explored from various perspectives highlighting, for example, phylogenetic groupings, pathovars as well as a wide range of O serotypes. The highly variable O-antigen, the most external part of the lipopolysaccharide component of the outer membrane of E. coli, is linked to the innermost lipid A through the core region of LPS of which 5 different structures, denominated K-12, R1, R2, R3 and R4, have been characterized so far. The aim of the present study was to analyze the prevalence of these LPS core types in the E. coli species and explore their distribution in the different E. coli phylogenetic groups and in relationship with the virulence gene repertoire. Results indicated an uneven distribution of core types between the different phylogroups, with phylogroup A strains being the most diverse in terms of LPS core types while phylogroups B1, D and E strains were dominated by the R3 type and phylogroups B2 and C strains being dominated by the R1 type. Strains carrying the LEE virulence operon were mostly of the R3 type whatever the phylogroup while, within phylogroup B2, strains carrying a K-12 core all belonged to the complex STc131, one of the major clone of extra-intestinal pathogenic E. coli (ExPEC) strains. The origin of this uneven distribution is discussed but remains to be explained, as well as the consequences of carrying a specific core type on the physiology of the bacteria. IMPACT STATEMENTThe diversity of the E. coli species in terms of type of infections is well known, and its surface O-antigen which shows some correspondence to pathogenicity. This study is the first one to report in detail the diversity and distribution of the LPS core types in the E. coli species using whole genome sequences. This distribution of the 5 know core types is analyzed in the different phylogroups along with their association with specific virulence gene repertoire. Results indicate a non-random distribution of LPS core types in the E. coli species and, most interestingly, preferential association of certain core types with either some phylogenetic clades or with particular virulence gene repertoires. This work is a first step towards the identification of the origin of this diversity as well as towards the exploration of the physiological properties associated with specific core types. DATA SUMMARYComplete list of strains with associated data is available in supplementary table S1.