Acinetobacter species are free-living, non-fermentative, Gram-negative bacteria, some of which have become important as opportunistic pathogens, often characterised by multiple drag resistance. Of the various genomospecies currently recognised, Acinetobacter baumannii is the one most commonly associated with nosocomial colonisation and infection, and many typing methods have been evaluated for the epidemiological monitoring of clinical isolates. Typing of strains by their heat-stable antigens [assumed to be the O-specific side-chains of lipopolysaccharide (LPS)] has not been used extensively, but 34 O serogroups have been recognised. During the course of a systematic study of the surface polysaccharides of A. baumannii, we have confirmed the presence of O-specific polymers in LPS extracts from the reference strain for serogroups O2, O5, O10, and O11, as well as strain 214 (a clinical isolate). In each case the polymer had a branched, oligosaccharide repeating-unit incorporating at least one amino sugar residue, features also found in polymers isolated from other O serogroups. Here we report the structure of the O16 polymer, which probably also occurs as a minor polysaccharide in O11 reference strain.

Lipopolysaccharide, structure, Acinetobacter baumannii, surface polysaccharide, O16 O-antigen

13C NMR data:
Linkage	Residue	C1	C2	C3	C4	C5	C6
3,4,2	Ac
3,4	aDGlcpN	97.20	54.14	70.8	69.6	70.7	64.71
3,2	Ac
3,3	bDGlcp	105.04	73.19	75.71	69.84	75.71	60.88
3	aDGalpN	97.34	48.88	76.83	75.17	70.92-71.77	59.75-60.33
2	Ac
	aDGlcpN	97.20	52.13	75.9	72.10	70.92-71.77	59.75-60.33


1H NMR data:
Linkage	Residue	H1	H2	H3	H4	H5	H6
3,4,2	Ac	-	2.01-2.06
3,4	aDGlcpN	4.99	3.90	3.86	3.68	4.34	3.66-4.07
3,2	Ac	-	2.01-2.06
3,3	bDGlcp	4.42	3.09	3.46	3.36	3.38	3.70-3.85
3	aDGalpN	5.46	4.47	3.83	4.28	?	3.8
2	Ac	-	2.01-2.06
	aDGlcpN	4.88	4.06	3.94	3.72	?	3.6-3.7


1H/13C HSQC data:
Linkage	Residue	C1/H1	C2/H2	C3/H3	C4/H4	C5/H5	C6/H6
3,4,2	Ac	NMR TSV error 2: unequal length of 13C and 1H datasets
3,4	aDGlcpN	97.20/4.99	54.14/3.90	70.8/3.86	69.6/3.68	70.7/4.34	64.71/3.66-4.07
3,2	Ac	NMR TSV error 2: unequal length of 13C and 1H datasets
3,3	bDGlcp	105.04/4.42	73.19/3.09	75.71/3.46	69.84/3.36	75.71/3.38	60.88/3.70-3.85
3	aDGalpN	97.34/5.46	48.88/4.47	76.83/3.83	75.17/4.28	70.92-71.77/?	59.75-60.33/3.8
2	Ac	NMR TSV error 2: unequal length of 13C and 1H datasets
	aDGlcpN	97.20/4.88	52.13/4.06	75.9/3.94	72.10/3.72	70.92-71.77/?	59.75-60.33/3.6-3.7

There is only one chemically distinct structure:

SVGMWSMILES3D molIonize

 

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

771.723 g/mol (C₃₀H₄₉R₂N₃O₂₀, R = next and previous repeats, not counted in mol weight)