Structural and genetic characterization of enterohemorrhagic Escherichia coli O145 O antigen and development of an O145 serogroup-specific PCR assay

Abstract

Enterohemorrhagic Escherichia coli O145 strains are emerging as causes of hemorrhagic colitis and hemolytic uremic syndrome. In this study, we present the structure of the E. coli O145 O antigen and the sequence of its gene cluster. The O145 antigen has repeat units containing three monosaccharide residues: 2-acetamido-2-deoxy-D-glucose (GlcNAc), 2-acetamidoylamino-2,6-dideoxy-L-galactose, and N-acetylneuraminic acid. It is very closely related to Salmonella enterica serovar Touera and S. enterica subsp. arizonae O21 antigen. The E. coli O145 gene cluster is located between the JUMPStart sequence and the gnd gene and consists of 15 open reading frames. Putative genes for the synthesis of the O-antigen constituents, for sugar transferase, and for O-antigen processing were annotated based on sequence similarities and the presence of conserved regions. The putative genes located in the E. coli O145 O-antigen gene cluster accounted for all functions expected for synthesis of the structure. An E. coli O145 serogroup-specific PCR assay based on the genes wzx and wzy was also developed by screening E. coli and Shigella isolates of different serotypes.

FIG. 1.

¹³C-NMR spectrum of trisaccharide 1 obtained by mild acid degradation of the E. coli O145 LPS. Arabic numerals refer to carbons in sugar residues. F, FucN; G, GlcN; N, Neu.

FIG. 2.

O-polysaccharide structures of E. coli O145 S. enterica serovar Toucra O48 (29a), and S. enterica subsp. arizonae O21 (59). OAc, acetyl. FucNAm is 2-acetimidoylamino-2,6-dideoxygalactose. In the original paper on S. enterica serovar Toucra O48 (29a), FucNA was misidentified as FucNAc.

FIG. 3.

O-antigen gene cluster of E. coli O145. All the genes are transcribed in the direction from galF to gnd. The shaded areas represent significant intergenic regions.