Escherichia coli strains are normally identified by the combination of their O and H (and sometimes K) antigens, and serotyping based on the antigens is believed to be crucial for clinical detection and epidemiological investigation. Two E. coli strains, G5413 and G5287, were isolated from faecal samples of female patients with diarrhoea and were not agglutinated with any antisera that cover the well-known O serogroups of E. coli. We elucidated the O-polysaccharide (OPS) structures and analysed the O-antigen gene clusters of these bacteria. The OPS structure of G5413 established by monosaccharide analysis and NMR spectroscopy was found to be unique amongst known bacterial polysaccharide structures. The O-antigen gene cluster of this strain was sequenced and did not match sequence data with any of the 184 O serogroups that have been recognized internationally. Gene functions were tentatively assigned and were appropriate to the OPS structure. Based on these data, we suggest G5413 as a candidate for a new E. coli O serogroup. Both the OPS structure and O-antigen gene cluster of G5287 were identical to those of E. coli L-19, a candidate for another new O serogroup characterized by us recently. Recognition of these two provisional O serogroups increases the number of known O-antigen forms of E. coli to 186.

O-antigen, Escherichia coli, serotyping

13C NMR data:
Linkage	Residue	C1	C2	C3	C4	C5	C6
3,3,2,2	Ac	174.7-175.2	23.6-23.9
3,3,2,4	bLRhap	102.4	71.6	74.1	73.3	73.5	17.9
3,3,2	aDGlcpN	97.0	54.4	76.3	76.6	72.0	61.8
3,3	bDGlcp	104.4	77.8	76.0	70.3	76.8	61.8
3	aLRhap	102.3	71.3	81.4	71.8	70.4	17.8
2	Ac	174.7-175.2	23.6-23.9
	bDGlcpN	101.1	57.3	83.2	70.4	77.1	62.4


1H NMR data:
Linkage	Residue	H1	H2	H3	H4	H5	H6
3,3,2,2	Ac	-	2.02-2.11
3,3,2,4	bLRhap	4.87	4.19	3.57	3.38	3.39	1.31
3,3,2	aDGlcpN	5.45	4.05	4.21	3.73	4.07	3.85-3.88
3,3	bDGlcp	4.75	3.47	3.59	3.46	3.44	3.76-3.88
3	aLRhap	4.89	3.99	3.75	3.48	3.95	1.24
2	Ac	-	2.02-2.11
	bDGlcpN	4.60	3.67	3.67	3.42	3.41	3.75-3.97


1H/13C HSQC data:
Linkage	Residue	C1/H1	C2/H2	C3/H3	C4/H4	C5/H5	C6/H6
3,3,2,2	Ac		23.6-23.9/2.02-2.11
3,3,2,4	bLRhap	102.4/4.87	71.6/4.19	74.1/3.57	73.3/3.38	73.5/3.39	17.9/1.31
3,3,2	aDGlcpN	97.0/5.45	54.4/4.05	76.3/4.21	76.6/3.73	72.0/4.07	61.8/3.85-3.88
3,3	bDGlcp	104.4/4.75	77.8/3.47	76.0/3.59	70.3/3.46	76.8/3.44	61.8/3.76-3.88
3	aLRhap	102.3/4.89	71.3/3.99	81.4/3.75	71.8/3.48	70.4/3.95	17.8/1.24
2	Ac		23.6-23.9/2.02-2.11
	bDGlcpN	101.1/4.60	57.3/3.67	83.2/3.67	70.4/3.42	77.1/3.41	62.4/3.75-3.97

There is only one chemically distinct structure:

SVGMWSMILES3D molIonize

 

*O[C@H]1[C@H](O[C@H]2O[C@@H](C)[C@H](O)[C@@H](O)[C@H]2O)[C@@H](CO)O[C@H](O[C@H]2[C@H](O[C@@H]3[C@@H](O)[C@H](C)O[C@@H](O[C@@H]4[C@@H](NC(C)=O)[C@H](*)O[C@H](CO)[C@H]4O)[C@@H]3O)O[C@H](CO)[C@@H](O)[C@@H]2O)[C@@H]1NC(C)=O

860.813 g/mol (C₃₄H₅₆R₂N₂O₂₃, R = next and previous repeats, not counted in mol weight)