Structure of a surface polysaccharide from Acinetobacter baumannii strain 214

Detection of lipid A by monoclonal antibodies in S-form lipopolysaccharide after acidic treatment of immobilized LPS on Western blot

Lipopolysaccharides (LPSs) were separated by SDS-PAGE, transferred onto polyvinylidene difluoride membranes, and hydrolyzed under acid conditions known to liberate lipid A from a broad variety of bacterial species. Independent of whether bis- or monophosphorylated lipid was set free, it remained bound to the membrane during subsequent immunostaining with monoclonal antibodies (MAbs) specific for the 1,4'-bis- or 4'-monophosphorylated lipid A backbone. Lipid A could be detected in the smooth (S)-form LPS from Enterobacteriaceae (Salmonella enterica, Citrobacter, Escherichia coli, Klebsiella pneumoniae, Serratia marcescens and Yersinia enterocolitica) , Pseudomonas aeruginosa, Chromobacterium violaceum, Acinetobacter, Vibrio cholerae and Legionella pneumophila, thus allowing LPS-phenotype determination. The procedure can be used for the majority of Gram-negative bacteria, since LPSs containing 2,3-diamino-2,3-dideoxy-glucose or glucosamine in the lipid A disaccharide backbone could be detected. It was shown to be sensitive (up to 20 ng of hydrolyzed LPS could be detected), and could be easily performed using isolated LPS or whole-cell lysates with or without prior digestion with proteinase K. In addition to opening several other application possibilities, the procedure may be particularly useful in cases where silver-staining of the O-chain in SDSpolyacrylamide gels fails and specific antibodies against the O-antigen are not available.

Structure of the K2 capsule associated with the KL2 gene cluster of Acinetobacter baumannii

The repeat unit structure of the K2 capsule from an extensively antibiotic-resistant Acinetobacter baumannii global clone 2 (GC2) strain was determined. The oligosaccharide contains three simple sugars, d-glucopyranose, d-galatopyranose and N-acetyl-d-galactosamine, and the complex sugar, 5,7-diacetamido-3,5,7,9-tetradeoxy-l-glycero-l-manno-non-2-ulosonic acid (Pse5Ac7Ac or pseudaminic acid), which has not previously been reported in any A. baumannii capsule. The strain was found to carry all the genes required for the synthesis of the sugars and construction of the K2 structure. The linkages catalyzed by the initiating transferase, three glycosyltransferases and the Wzy polymerase were also predicted. Examination of publicly available A. baumannii genome sequences revealed that the same gene cluster, KL2, often occurs in extensively antibiotic-resistant GC2 isolates and in further strain types. The gene module responsible for the synthesis of pseudaminic acid was also detected in four other K loci. A related module including genes for an acylated relative of pseudaminic acid was also found in two new KL types. A polymerase chain reaction scheme was developed to detect all modules containing genes for sugars based on pseudaminic acid and to specifically detect KL2.

Variation in the complex carbohydrate biosynthesis loci of Acinetobacter baumannii genomes

Extracellular polysaccharides are major immunogenic components of the bacterial cell envelope. However, little is known about their biosynthesis in the genus Acinetobacter, which includes A. baumannii, an important nosocomial pathogen. Whether Acinetobacter sp. produce a capsule or a lipopolysaccharide carrying an O antigen or both is not resolved. To explore these issues, genes involved in the synthesis of complex polysaccharides were located in 10 complete A. baumannii genome sequences, and the function of each of their products was predicted via comparison to enzymes with a known function. The absence of a gene encoding a WaaL ligase, required to link the carbohydrate polymer to the lipid A-core oligosaccharide (lipooligosaccharide) forming lipopolysaccharide, suggests that only a capsule is produced. Nine distinct arrangements of a large capsule biosynthesis locus, designated KL1 to KL9, were found in the genomes. Three forms of a second, smaller variable locus, likely to be required for synthesis of the outer core of the lipid A-core moiety, were designated OCL1 to OCL3 and also annotated. Each K locus includes genes for capsule export as well as genes for synthesis of activated sugar precursors, and for glycosyltransfer, glycan modification and oligosaccharide repeat-unit processing. The K loci all include the export genes at one end and genes for synthesis of common sugar precursors at the other, with a highly variable region that includes the remaining genes in between. Five different capsule loci, KL2, KL6, KL7, KL8 and KL9 were detected in multiply antibiotic resistant isolates belonging to global clone 2, and two other loci, KL1 and KL4, in global clone 1. This indicates that this region is being substituted repeatedly in multiply antibiotic resistant isolates from these clones.

The structure of the polysaccharide O-chain of the LPS from Acinetobacter baumannii strain ATCC 17961

The gram-negative bacterium Acinetobacter baumannii strain ATCC17961 has been used by several laboratories in mouse models of respiratory A. baumannii infection, and a study of the role of its lipopolysaccharide in the pathogenicity is of interest. The structure of the O-deacylated polysaccharide O-chain component of its LPS has been determined by 2D NMR spectroscopy and mass spectrometry methods, and by the structural identification of oligosaccharides obtained by sequential application of the Smith degradation of the O-antigen. The O-chain was determined to be a polymer of a branched pentasaccharide repeating unit composed of 2,3-diacetamido-2,3-dideoxy-D-glucuronic acid, 2-acetamido-2-deoxy-D-glucose, 2-acetamido-2-deoxy-D-galactose, D-glucose, and D-galactose, and has the following structure: [carbohydrate sequence see in text].

Structure of the O-specific polysaccharide for Acinetobacter baumannii serogroup O1

A polymeric fraction containing D-galactose, N-acetyl-D-galactosamine, and N-acetyl-D-glucosamine was isolated from the lipopolysaccharide produced by the reference strain for Acinetobacter baumannii serogroup O1. By means of NMR spectroscopy, methylation analysis, and chemical degradation, the repeating unit of the polymer was identified as a branched trisaccharide of the following structure. [formula: see text].

Structure of the O-7 antigen from Acinetobacter baumannii

The polymeric O-antigen was isolated from the lipopolysaccharide of the reference of the reference strain for Acinetobacter baumannii serogroup O-7. Both the lipopolysaccharide and the isolated polymer reacted with the homologous antiserum. Monosaccharide analyses and NMR spectra showed that the polymer had a hexasaccharide repeating unit constructed from residues of L-rhamnose (4) and N-acetyl-D-glucosamine (2). The following structure for the repeating unit was established by means of detailed interpretation of the NMR spectra, methylation analysis, and chemical degradations. The tetrasaccharide backbone is identical to that for the O-10 antigen of A. baumannii, which has alpha-D-ManpNAc as the lateral substituent in place of the disaccharide present in the O-7 antigen. [formula: see text]

Structural studies of the putative O-specific polysaccharide of Acinetobacter baumannii O24 containing 5,7-diamino-3,5,7,9-tetradeoxy-L-glycero-D-galacto-nonulosonic acid

A polysaccharide containing D-GlcN, 2-amino-2,6-dideoxy-L-galactose (L-FucN), and 7-acetamido-5-acylamino-3,5,7,9-tetradeoxy-L-glycero-D-galacto-nonulo sonic acid (LegAX), in which the acyl group (X) is either S-3-hydroxybutyryl (50%) or acetyl (50%), was isolated by mild acid hydrolysis treatment, followed by gel-permeation chromatography, of the water-soluble lipopolysaccharide from Acinetobacter baumannii serogroup O24. The polysaccharide, characterised by means of monosaccharide analyses, partial acid hydrolysis, methylation analysis and NMR studies, was shown to have a linear tetrasaccharide repeating unit, as depicted below. Serological tests indicated that the polymer corresponded to the O24 antigen. -->6)-alpha-D-GlcpNAc-(1-->3)-alpha-L-FucpNAc-(1-->3)-alpha-D-Glcp NAc-(1-->4)-beta-LegpAX-(1-->.

Structure of the O18 antigen from Acinetobacter baumannii

The polymeric O antigen was obtained from lipopolysaccharide extracted from isolated, defatted cell walls of the reference strain for Acinetobacter baumannii serogroup O18. Monosaccharide analyses and NMR spectra established that the polymer had a regular structure with a repeating unit based on residues of D-galactose (2), N-acetyl-D-galactosamine (1), and N-acetyl-D-mannosamine (1). Further interpretation of the NMR spectra, combined with the results of methylation analysis and a Smith degradation, showed that the repeating unit had the following structure. beta-D-ManpNAc-(1-->4)-alpha-D-Galp 1 decreases 4 -->3)-beta-D-GalpNAc-(1-->3)-beta-D-Galp-(1-->.

Structural and serological characterisation of the O-antigenic polysaccharide of the lipopolysaccharide from Acinetobacter junii strain 65

A polysaccharide containing rhamnose (Rha) and Gal was isolated by acetic acid hydrolysis, followed by gel-permeation chromatography, from the water-soluble lipopolysaccharide (phenol/water extracted) from Acinetobacter junii strain 65. The polysaccharide was characterised by means of monosaccharide analyses, Smith degradation, and NMR studies, and was shown to have a linear pentasaccharide repeating unit, as depicted below. This structure was specifically recognised in western blots and enzyme immunoassays by polyclonal rabbit antisera. [structure in text]

Structures of polymeric products isolated from the lipopolysaccharides of reference strains for Acinetobacter baumannii O23 and O12

A polysaccharide containing D-galactose (Gal), 2-acetamido-2-deoxy-D-galactose (GalNAc), 2-acetamido-2-deoxy-D-glucose (GlcNAc), and 3-deoxy-3-(D-3-hydroxybutyramido)-D-quinovose (Qui3NR) was isolated from lipopolysaccharide (LPS) obtained from cells walls of the reference strain for Acinetobacter baumannii O23. By means of NMR studies, methylation analysis, and chemical degradations, the repeating unit of the polymer was identified as a branched pentasaccharide with the structure 1. The same polymer was apparently also present in LPS of the reference strain for serogroup O12, together with a second polymer based on a branched tetrasaccharide with the structure 2. This second polymer has previously been isolated as the O16 antigen of A. baumannii [Haseley, S.R., Diggle, H.J. & Wilkinson, S. G. (1996) Carbohydr. Res. 293, 259-265] and is probably present as a minor component of the LPS of A. baumannii O11 [Haseley, S.R. & Wilkinson, S.G. (1996) Eur. J. Biochem. 237, 266-271]. [Sequence: see text]

High-field NMR as a technique for the determination of polysaccharide structures

NMR spectroscopy has played a developing role in the study of polysaccharide structures for over 30 years. Many new bacterial polysaccharide repeat unit structures have recently been published as a result of the application of modern NMR techniques. NMR can also be used to elucidate the structures of both regular and heterogeneous polysaccharides from fungal and plant sources, as well as complex glycosaminoglycans of animal origin. In addition to covalent structure, conformation and dynamics of polysaccharides are susceptible to NMR analysis, both in solution and in the solid state. Improvements in NMR technology with potential applications to polysaccharide studies hold promise for the future.

Structural and serological characterisation of two O-specific polysaccharides of Acinetobacter

Extraction of dry bacteria of Acinetobacter strain 34 (DNA group 2) or Acinetobacter strain 108 (DNA group 13) by phenol/water yielded a polymer that was identified by means of serological studies and fatty acid analysis as S-form lipopolysaccharide. Degradation of the lipopolysaccharides of strains 34 and 108 in 1% acetic acid and 5% acetic acid, respectively, and gel-permeation chromatography gave the respective O-antigenic polysaccharides, the structures of which were determined, by compositional analysis and NMR spectroscopy of the polysaccharide, as [Sequence: see text] for strain 108, where D-Fucp3NBuOH represents 3-[(R)-3-hydroxybutyramido] -3,6-dideoxy-D-galactose and D-GalpANAc represents 2-acetamido-2-deoxy-D-galacturonic acid. Both structures were specifically recognised in Western blots by polyclonal rabbit antisera and there was no cross-reaction between these two structures.

Structure of the O-specific polysaccharide of Acinetobacter baumannii O5 containing 2-acetamido-2-deoxy-D-galacturonic acid

A polysaccharide containing 2-acetamido-2-deoxy-D-glucose (GlcNAc), 2-acetamido-2-deoxy-L-fucose (FucNAc), and 2-acetamido-2-deoxy-D-galacturonic acid (GalNAcA) was isolated from an aqueous phenol extract of lipid-free, isolated cell walls of the reference strain for Acinetobacter baumannii serogroup O5, by mild acid hydrolysis of the extract and chromatography of the water-soluble products on Sephadex G-50. By means of NMR studies, methylation analysis, carboxyl reduction and chemical degradations, the repeating unit of the polymer was identified as a branched tetrasaccharide of the structure shown. The serologically active polymer is believed to correspond to the side chain of the O5 lipopolysaccharide: [table: see text]

Structural studies of the putative O-specific polysaccharide of Acinetobacter baumannii O11

A major polysaccharide containing D-galactose, D-glucose and 2-acetamido-2-deoxy-D-galactose was obtained after mild acid hydrolysis of the water-soluble material released by treatment of cell walls from Acinetobacter baumannii strain O11 with hot, aqueous phenol. By means of NMR studies, Smith degradation and N-deacetylation/deamination, the repeating unit of the polymer was identified as a branched pentasaccharide of the structure shown. Also present was a minor polymer containing glucose, 2-acetamido-2-deoxyglucose-and 2-acetamido-2-deoxygalactose, the structure of which was not elucidated. On serological testing, the polymeric material was shown to correspond to the O-antigenic moiety of the parent extract (assumed to be lipopolysaccharide) and circumstantial evidence indicated that O11 specificity was conferred by the major polymer. [formula: see text]

Structural studies of the putative O-specific polysaccharide of Acinetobacter baumannii O2 containing 3,6-dideoxy-3-N-(D-3-hydroxybutyryl)amino-D-galactose

A polysaccharide containing D-galactose, 2-deoxy-2-N-acetylamino-D-galactose and 3,6-dideoxy-3-N-(D-3-hydroxybutyryl)amino-D-galactose, probably corresponding to the lipopolysaccharide side chain, was obtained from an aqueous phenol extract of isolated cell walls from Acinetobacter baumannii strain O2. By means of NMR studies and chemical degradations, the repeating unit of the polymer was identified as a branched hexasaccharide of the structure shown, where Fuc3N represents 3-amino-3,6-dideoxygalactose and R represents D-3-hydroxybutyryl. Serological tests indicated that the polymer corresponded to the O2 antigen.

Structure of the putative O10 antigen from Acinetobacter baumannii

A polysaccharide containing L-rhamnose, 2-acetamido-2-deoxy-D-glucose, and 2-acetamido-2-deoxy-D-mannose was obtained from an aqueous phenol extract of isolated cell walls from the reference strain for Acinetobacter baumannii serogroup O10. By means of NMR studies and chemical degradations, the repeating unit of the polymer (the putative O10 antigen) was identified as a branched pentasaccharide of the structure shown.