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1. (Article ID: 125)
 
Tsvetkov YE, Shashkov AS, Knirel YA, Zähringer U
Synthesis and identification in bacterial lipopolysaccharides of 5,7-diacetamido-3,5,7,9-tetradeoxy-D-glycero-D-galacto- and -D-glycero-D-talo-nonulosonic acids
Carbohydrate Research 331(3) (2001) 233-237
 

5,7-Diacetamido-3,5,7,9-tetradeoxy-D-glycero-D-galacto- and -D-glycero-D-talo-non-2-ulosonic acids were synthesized by condensation of 2,4-diacetamido-2,4,6-trideoxy-D-mannose with oxalacetic acid. Comparison of the 1H and 13C NMR data and the specific optical rotation values of these monosaccharides and the corresponding L-glycero-D-galacto and L-glycero-D-talo isomers synthesized earlier [Tsvetkov, Y. E.; Shashkov, A. S.; Knirel, Y. A.; Backinowsky, L. V.; Zähringer, U. Mendeleev Communications. 2000, 90-92] with data of the natural compounds enabled the identification in bacterial lipopolysaccharides of derivatives of 5,7-diamino-3,5,7,9-tetradeoxy-D-glycero-D-galacto-non-2-ulosonic (legionaminic) acid and epimers of legionaminic acid at C-4 and C-8.

synthesis, 5, 7-diamino-3, 7, Legionella pneumophila, 9-tetradeoxynon-2-ulosonic acid, identification of legionaminic acid, lipopolysaccharide components

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2. (Article ID: 3676)
 
Choi AH, Slamti L, Avci FY, Pier GB, Maira-Litran T
The pgaABCD locus of Acinetobacter baumannii encodes the production of poly-β-1-6-N-acetylglucosamine, which is critical for biofilm formation
Journal of Bacteriology 191(19) (2009) 5953-5963
 

We found that Acinetobacter baumannii contains a pgaABCD locus that encodes proteins that synthesize cell-associated poly-β-(1-6)-N-acetylglucosamine (PNAG). Both a mutant with an in-frame deletion of the pga locus (S1∆pga) and a transcomplemented strain (S1∆pga-c) of A. baumannii were constructed, and the PNAG production by these strains was compared using an immunoblot assay. Deleting the pga locus resulted in an A. baumannii strain without PNAG, and transcomplementation of the S1∆pga strain with the pgaABCD genes fully restored the wild-type PNAG phenotype. Heterologous expression of the A. baumannii pga locus in Escherichia coli led to synthesis of significant amounts of PNAG, while no polysaccharide was detected in E. coli cells harboring an empty vector. Nuclear magnetic resonance analysis of the extracellular polysaccharide material isolated from A. baumannii confirmed that it was PNAG, but notably only 60% of the glucosamine amino groups were acetylated. PCR analysis indicated that all 30 clinical A. baumannii isolates examined had the pga genes, and immunoblot assays indicated that 14 of the 30 strains strongly produced PNAG, 14 of the strains moderately to weakly produced PNAG, and 2 strains appeared to not produce PNAG. Deletion of the pga locus led to loss of the strong biofilm phenotype, which was restored by complementation. Confocal laser scanning microscopy studies combined with COMSTAT analysis demonstrated that the biovolume, mean thickness, and maximum thickness of 16-h and 48-h-old biofilms formed by wild-type and pga-complemented A. baumannii strains were significantly greater than the biovolume, mean thickness, and maximum thickness of 16-h and 48-h-old biofilms formed by the S1∆pga mutant strain. Biofilm-dependent production of PNAG could be an important virulence factor for this emerging pathogen that has few known virulence factors

Bacterial Proteins, Gene Expression Regulation, Bacterial, Acinetobacter baumannii, biofilms, beta-glucans

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3. (Article ID: 3849)
 
Gening M, Maira-Litran T, Kropec A, Skurnik D, Grout M, Tsvetkov YE, Nifantiev NE, Pier GB
Synthetic b-(1->6)-linked N-acetylated and non-acetylated oligoglucosamines to produce conjugate vaccines for bacterial pathogens
Infection and Immunity 78(2) (2010) 764-772
 

Vaccines for pathogens usually target strain-specific surface antigens or toxins and rarely is there broad antigenic specificity extending across multiple species. Protective antibodies for bacteria are usually specific for surface or capsular antigens. β-(1→6)-poly-N-acetyl-d-glucosamine (PNAG) is a surface polysaccharide produced by many pathogens, including Staphylococcus aureus, Escherichia coli, Yersinia pestis, Bordetella pertussis, Acinetobacter baumannii and others. Protective antibodies to PNAG are elicited when a deacetylated glycoform (dPNAG, <30% acetates) is used in conjugate vaccines whereas highly acetylated PNAG does not induce such antibodies. Chemical derivation of dPNAG from native PNAG is imprecise, so we synthesized both β-(1→6)-d-glucosamine (GlcNH2) and β-(1→6)-d-N-acetylglucosamine (GlcNAc) oligosaccharides with linkers on the reducing terminus that could be activated to produce sulfhydryl groups for conjugation to bromacetyl groups introduced onto carrier proteins. Synthetic 5- or 9-mer GlcNH2 conjugated to tetanus toxoid (TT) elicited mouse antibodies that mediated opsonic killing of multiple S. aureus strains, while the antibodies that were produced to the 5- or 9-mer GlcNAc-TT did not mediate opsonic killing. Rabbit antibodies to 9GlcNH2-TT bound to PNAG and dPNAG antigens, mediated killing of S. aureus and E. coli, and protected against S. aureus skin abscesses and lethal E. coli peritonitis. Chemical synthesis of a series of oligoglucosamine ligands with defined differences in N-acetylation allowed us to identify a conjugate vaccine formulation that generated protective immune responses to two of the most challenging bacterial pathogens. This vaccine could potentially be used to engender protective immunity to the broad range of pathogens that produce surface PNAG.

vaccines, conjugate, β-Glucans, Escherichia coli Infections, peritonitis, Staphylococcal Skin Infections

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4. (Article ID: 4050)
 
Knirel YA, Shevelev SD, Perepelov AV
Higher aldulosonic acids: components of bacterial glycans
Mendeleev Communications 21(4) (2011) 173-182
 

Recent data on the natural occurrence, chemistry, and biochemistry of C8 and C9 aldulosonic acids (3-deoxy-d-manno-oct-2-ulosonic acid, sialic acids, N-acyl derivatives of 5,7-diamino-3,5,7,9-tetradeoxynon-2-ulosonic acids, and some others) as well as on the structures and biological significance of bacterial glycans containing these higher acidic monosaccharides are summarized.

structure, Bacterial, glycan, aldulosonic acid, higher acidic monosaccharides, sialic acids

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5. (Article ID: 4610)
 
Russo TA, Beanan JM, Olson R, Macdonald U, Cox AD, St Michael F, Vinogradov EV, Spellberg B, Luke-Marshall NR, Campagnari AA
The K1 Capsular Polysaccharide From Acinetobacter baumannii Is a Potential Therapeutic Target Via Passive Immunization
Infection and Immunity 81(3) (2013) 915-922
 

The emergence of extreme and pan-resistant gram-negative bacilli, such as Acinetobacter baumannii requires consideration of non-antimicrobial therapeutic approaches. The goal of this report was to evaluate the K1 capsular polysaccharide from A. baumannii as a passive immunization target. Its structure was determined by a combination of mass spectrometric and NMR techniques. Molecular mimics that might raise the concern for autoimmune disease were not identified. Immunization of CD1 mice demonstrated that the K1 capsule is immunogenic. The monoclonal antibody MAb13D6, which is directed against the K1 capsule from A. baumannii, was used to determine the seroprevalence of the K1 capsule in a collection of 100 A. baumannii strains. Thirteen percent of the A. baumannii isolates from this collection were seroreactive to MAb13D6. Opsonization of K1-positive strains, but not K1-minus strains, with MAb13D6 significantly increased neutrophil-mediated bactericidal activity in vitro (P < 0.05). Lastly, treatment with MAb13D6 three and twenty-four h after bacterial challenge in a rat soft-tissue infection model resulted in a significant decrease in the growth/survival a K1-positive strain compared to a K1-minus strain or to treatment with a vehicle control (P <0.0001). These data support the proof of principle that the K1 capsule is a potential therapeutic target via passive immunization. Other serotypes require assessment and pragmatic challenges exist such as the need to serotype infecting strains and utilize serotype-specific therapy. Nonetheless, this approach may become an important therapeutic option with increasing antimicrobial resistance and a diminishing number of active antimicrobials.

Acinetobacter baumannii, monoclonal antibodies, immunization, serotype-specific, capsular polysaccharid

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6. (Article ID: 4762)
 
Kenyon JJ, Marzaioli AM, Hall RM, De Castro C
Structure of the K6 capsular polysaccharide from Acinetobacter baumannii isolate RBH4
Carbohydrate Research 409 (2015) 30-35
 

The structure of the capsular polysaccharide (CPS) from an Acinetobacter baumannii global clone 2 (GC2) clinical isolate RBH4 that carries the KL6 gene cluster was elucidated by means of chemical and spectroscopical methods. The repeating unit of K6 CPS is linear and contains N-acetyl-D-galactosamine (D-GalpNAc), two D-galactose (D-Galp) residues and 5,7-di-N-acetylpseudaminic acid (Pse5Ac7Ac). The synthesis of these sugars could be attributed to genes in the KL6 capsule biosynthesis gene cluster, and the formation of the linkages between the sugars were assigned to glycosyltransferases or the Wzy polymerase encoded in KL6.

Acinetobacter baumannii, capsular polysaccharide, NMR spectroscopy, pseudaminic acid, K locus, KL6 gene cluster

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7. (Article ID: 4973)
 
Kosma P
Progress in Kdo-glycoside chemistry
Tetrahedron Letters 57(20) (2016) 2133-2142
 

Glycosylation chemistry of 3-deoxy-D-manno-oct-2-ulosonic acid units has been considerably developed within the last decade. This review covers major achievements with respect to improved yields and anomeric selectivity as well as suppression of the elimination side reaction via selection of dedicated protecting groups and appropriate activation of the anomeric center.

synthesis, oligosaccharide, 3-deoxy-D-manno-oct-2-ulosonic acid, Kdo, glycosyl donor, Glycal

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8. (Article ID: 5188)
 
Micoli F, Costantino P, Adamo R
Potential targets for next generation anti-microbial glycoconjugate vaccines
FEMS Microbiology Reviews 42(3) (2018) 388-423
 

Cell surface carbohydrates have been proven optimal targets for vaccine development. Conjugation of polysaccharides to a carrier protein triggers a T-cell dependent immune response to the glycan moiety. Licensed glycoconjugate vaccines are produced by chemical conjugation of capsular polysaccharides to prevent meningitis caused by meningococcus, pneumococcus and Haemophilus influenzae type b. However, other classes of carbohydrates (O-antigens, exopolysaccharides, wall/teichoic acids) represent attractive targets for developing vaccines.Recent analysis from WHO/CHO underpins alarming concern towards antibiotic resistant bacteria, such as the so called ESKAPE pathogens (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa and Enterobacter spp.) and additional pathogens such as Clostridium difficile and Group A Streptococcus. Fungal infections are also becoming increasingly invasive for immunocompromised patients or hospitalized individuals. Other emergencies could derive from bacteria which spread during environmental calamities (Vibrio cholerae) or with potential as bioterrorism weapons (Burkholderia pseudomallei and mallei, Francisella tularensis). Vaccination could aid reducing the use of broad spectrum antibiotics and provide protection by herd immunity also to individuals who are not vaccinated.This review analyses structural and functional differences of the polysaccharides exposed on the surface of emerging pathogenic bacteria, combined with medical need and technological feasibility of corresponding glycoconjugate vaccines.

carbohydrates, glycoconjugates, vaccines, glycoengineering, antimicrobial resistance

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9. (Article ID: 5764)
 
Flannery A, Le Berre M, Pier GB, O'Gara JP, Kilcoyne M
Glycomics Microarrays Reveal Differential In Situ Presentation of the Biofilm Polysaccharide Poly-N-acetylglucosamine on Acinetobacter baumannii and Staphylococcus aureus Cell Surfaces
International Journal of Molecular Sciences 21(7) (2020) 2465
 

The biofilm component poly-N-acetylglucosamine (PNAG) is an important virulence determinant in medical-device-related infections caused by ESKAPE group pathogens including Gram-positive Staphylococcus aureus and Gram-negative Acinetobacter baumannii. PNAG presentation on bacterial cell surfaces and its accessibility for host interactions are not fully understood. We employed a lectin microarray to examine PNAG surface presentation and interactions on methicillin-sensitive (MSSA) and methicillin-resistant S. aureus (MRSA) and a clinical A. baumannii isolate. Purified PNAG bound to wheatgerm agglutinin (WGA) and succinylated WGA (sWGA) lectins only. PNAG was the main accessible surface component on MSSA but was relatively inaccessible on the A. baumannii surface, where it modulated the presentation of other surface molecules. Carbohydrate microarrays demonstrated similar specificities of S. aureus and A. baumannii for their most intensely binding carbohydrates, including 3' and 6'sialyllactose, but differences in moderately binding ligands, including blood groups A and B. An N-acetylglucosamine-binding lectin function which binds to PNAG identified on the A. baumannii cell surface may contribute to biofilm structure and PNAG surface presentation on A. baumannii. Overall, these data indicated differences in PNAG presentation and accessibility for interactions on Gram-positive and Gram-negative cell surfaces which may play an important role in biofilm-mediated pathogenesis

polysaccharide, Acinetobacter baumannii, Staphylococcus aureus, lectin, PNAG, Biofilm, bacterial adhesins, glycomics microarrays, poly-N-acetylglucosamine

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10. (Article ID: 6452)
 
Rogga V, Kosalec I
Untying the anchor for the lipopolysaccharide: lipid A structural modification systems offer diagnostic and therapeutic options to tackle polymyxin resistance
Arhiv za higijenu rada i toksikologiju = Archives of industrial hygiene and toxicology [Croatian] 74(3) (2023) 145-166
 

Polymyxin antibiotics are the last resort for treating patients in intensive care units infected with multiple-resistant Gram-negative bacteria. Due to their polycationic structure, their mode of action is based on an ionic interaction with the negatively charged lipid A portion of the lipopolysaccharide (LPS). The most prevalent polymyxin resistance mechanisms involve covalent modifications of lipid A: addition of the cationic sugar 4-amino-L-arabinose (L-Ara4N) and/or phosphoethanolamine (pEtN). The modified structure of lipid A has a lower net negative charge, leading to the repulsion of polymyxins and bacterial resistance to membrane disruption. Genes encoding the enzymatic systems involved in these modifications can be transferred either through chromosomes or mobile genetic elements. Therefore, new approaches to resistance diagnostics have been developed. On another note, interfering with these enzymatic systems might offer new therapeutic targets for drug discovery. This literature review focuses on diagnostic approaches based on structural changes in lipid A and on the therapeutic potential of molecules interfering with these changes.

lipid A, Gram-negative bacteria, MALDI-TOF-MS, antimicrobial resistance, adjuvants, MCR-1

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11. (Article ID: 6508)
 
Lü X, Li G, Pang J, Yang X, Cywes-Bentley C, You X, Pier GB
Antibodies targeting a conserved surface polysaccharide are protective against a wide range of microbial pathogens producing β-1–6-linked poly-N-acetylglucosamine (PNAG)
Engineering (Beijing) 38 (2024) 69-76
 

The β-1–6-linked poly-N-acetylglucosamine (PNAG) polymer is a conserved surface polysaccharide produced by many bacteria, fungi, and protozoan (and even filarial) parasites. This wide-ranging expression makes PNAG an attractive target for vaccine development, as it potentially encompasses a broad range of microorganisms. Significant progress has been made in discovering important properties of the biology of PNAG expression in recent years. The molecular characterization and regulation of operons for the production of PNAG biosynthetic proteins and enzymes have been studied in many bacteria. In addition, the physiological function of PNAG has been further elucidated. PNAG-based vaccines and PNAG-targeting antibodies have shown great efficacy in preclinical research. Furthermore, clinical tests for both vaccines and antibodies have been carried out in humans and economically important animals, and the results are promising. Although it is not destined to be a smooth road, we are optimistic about new vaccines and immunotherapeutics targeting PNAG becoming validated and eventually licensed for clinical use against multiple infectious agents

monoclonal antibody, conjugate vaccine, poly-N-acetylglucosamine

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