Distribution of core oligosaccharide types in lipopolysaccharides from Escherichia coli

In the lipopolysaccharides of Escherichia coli there are five distinct core oligosaccharide (core OS) structures, designated K-12 and R1 to R4. The ob jective of this work was to determine the prevalences of these core OS type s within the species. Unique sequences in the waa (core OS biosynthesis) ge ne operon were used to develop a PCR-based system that facilitated unequivo cal determination of the core OS types in isolates of E. coli, This system was applied to the 72 isolates in the E. coli ECOR collection, a compilatio n of isolates that is considered to be broadly representative of the geneti c diversity of the species. Fifty (69.4%) of the ECOR isolates contained th e R1 core OS, 8 (11.1%) were representatives of R2, 8 (11.1%) were R3, 2 (2 .8%) were R4, and only 4 (5.6%) were K-12. R1 is the only core OS type foun d in all four major phylogenetic groups (A, B1, B2, and D) in the ECOR coll ection. Virulent extraintestinal pathogenic E. coli isolates tend to be clo sely related to group B2 and, to a lesser extent, group D isolates. All of the ECOR representatives from the B2 and D groups had the R1 core OS. In co ntrast, commensal E. coli isolates are more closely related to group A, whi ch contains isolates representing each of the five tore OS structures. R3 w as the only core OS type found in 38 verotoxigenic E. coli (VTEC) isolates from humans and cattle belonging to the common enterohemorrhagic E. coli se rogroups O157, O111, and O26, Although isolates from other VTEC serogroups shelved more core OS diversity, the R3 type (83.1% of all VTEC isolates) wa s still predominant. When non-VTEC commensal isolates from cattle were anal yzed, it was found that most possessed the R1 core OS type.