Characterization of Burkholderia pseudomallei O antigens in different clinical strains

O antigen is the major component of lipopolysaccharide LPS. The chemical structure of the O antigen determines the LPS serospecificity of the bacteria, and the diversity of O antigen is the basis for serotyping Burkholderia pseudomallei. In this study, structural elucidation of type B O antigen obtained from a clinical B. pseudomallei strain was conducted, and the effects of different types of LPS on macrophage differentiation were investigated. The O antigen was found to be composed of repeating units of [→4)-α-L-Rhap(1 → 4)-α-L-Rhap(1→2)-α-L-Rhap(1 → 2)-α-L-Rhap(1 → 3)-α-L-Rhap(1 → 3)-α-L-Rhap(1 → 4)-α-L-Rhap(1 → 6)-α-D-Galp(1→]_n, where some of the →4)-α-L-Rhap(1 → units were substituted at O-3 by β-D-Xylp(1 → residues, and minor →3)-α-L-Rhap(1 → units were substituted at O-2 by β-D-Xylp(1 → residues. Meahwhile, the →6)-α-D-Galp(1 → units were substituted at O-3 by α-D-Galp(1 → residues. Furthermore, both type A and type B O antigens of B. pseudomallei could polarize macrophages toward the M1 phenotype, but the core oligosaccharides had no such activity. Therefore, we deduced that this polarization relies on the O antigen of LPS and might be related to the ability of B. pseudomallei to survive and replicate within macrophages. Thus, the characterization of different types of O antigen structural motifs is essential for further clarifying the persistence/survival mechanisms and inflammatory potential of B. pseudomallei.

In vitro and in vivo antimicrobial efficacy of natural plant-derived compounds against Vibrio cholerae of O1 El Tor Inaba serotype

In this study, we investigated antibacterial activities of 20 plant-derived natural compounds against Gram-negative enteric pathogens. We found that both flavonoids and non-flavonoids, including honokiol and magnolol, possess specific antibacterial activities against V. cholerae, but not against other species of Gram-negative bacterium which we tested. Using various antibacterial assays, we determined that there was a dose-dependent bactericidal and biofilm inhibitory activity of honokiol and magnolol against Vibrio cholerae. In addition to antibacterial activities, these molecules also induced an attenuating effect on reactive oxygen species (ROS) production and pro-inflammatory responses generated by macrophages in response to lipopolysaccharides (LPS). Additionally, Caenorhabditis elegans lethality assay revealed that honokiol and magnolol have an ability to extend a lifespan of V. cholerae-infected worms, contributing to prolonged survival of worms after lethal infection. Altogether, our data show for the first time that honokiol and magnolol may be considered as attractive protective or preventive food adjuncts for cholera.

VP2118 has major roles in Vibrio parahaemolyticus response to oxidative stress

BACKGROUND

Reactive oxygen species (ROS), including superoxide anion radical, induce chronic risk of oxidative damage to many cellular macromolecules resulting in damage to cells. Superoxide dismutases (SODs) catalyze the dismutation of superoxide to oxygen and hydrogen peroxide and are a primary defense against ROS. Vibrio parahaemolyticus, a marine bacterium that causes acute gastroenteritis following consumption of raw or undercooked seafood, can survive ROS generated by intestinal inflammatory cells. However, there is little information concerning SODs in V. parahaemolyticus. This study aims to clarify the role of V. parahaemolyticus SODs against ROS.

METHODS

V. parahaemolyticus SOD gene promoter activities were measured by a GFP reporter assay. Mutants of V. parahaemolyticus SOD genes were constructed and their SOD activity and resistance to oxidative stresses were measured.

RESULTS

Bioinformatic analysis showed that V. parahaemolyticus SODs were distinguished by their metal cofactors, FeSOD (VP2118), MnSOD (VP2860), and CuZnSOD (VPA1514). VP2118 gene promoter activity was significantly higher than the other SOD genes. In a VP2118 gene deletion mutant, SOD activity was significantly decreased and could be recovered by VP2118 gene complementation. The absence of VP2118 resulted in significantly lowered resistance to ROS generated by hydrogen peroxide, hypoxanthine-xanthine oxidase, or Paraquat. Furthermore, both the N- and C-terminal SOD domains of VP2118 were necessary for ROS resistance.

CONCLUSION

VP2118 is the primary V. parahaemolyticus SOD and is vital for anti-oxidative stress responses.

GENERAL SIGNIFICANCE

The V. parahaemolyticus FeSOD VP2118 may enhance ROS resistance and could promote its survival in the intestinal tract to facilitate host tissue infection.

Immunomodulatory efficiency of poly(2-oxazolines)

Poly(2-oxazolines) represent promising polymer materials for biomedical applications. The activation of mouse lymphoid macrophage line P388.D1 (clone 3124) by two selected representatives of poly(2-oxazolines), namely poly(2-ethyl-2-oxazoline) (PETOX100) and poly[2-(4-aminophenyl)-2-oxazoline-co-2-ethyl-2-oxazoline] (AEOX10), was assessed in vitro. The immunomodulatory efficacy of both polymers was evaluated via the induced release of pro-inflammatory cytokines (TNF-α, IL-1α and IL-6) and the acceleration of reactive free radicals. The present study revealed effective structure-immunomodulating associations of AEOX10 and PETOX100, which are desirable in biomedical and pharmaceutical applications of aliphatic and aromatic poly (2-oxazolines) in vivo.

Remodelling of the Vibrio cholerae membrane by incorporation of exogenous fatty acids from host and aquatic environments

The Gram-negative bacteria Vibrio cholerae poses significant public health concerns by causing an acute intestinal infection afflicting millions of people each year. V. cholerae motility, as well as virulence factor expression and outer membrane protein production, has been shown to be affected by bile. The current study examines the effects of bile on V. cholerae phospholipids. Bile exposure caused significant alterations to the phospholipid profile of V. cholerae but not of other enteric pathogens. These changes consisted of a quantitative increase and migratory difference in cardiolipin, decreases in phosphatidylglycerol and phosphatidylethanolamine, and the dramatic appearance of an unknown phospholipid determined to be lyso-phosphatidylethanolamine. Major components of bile were not responsible for the observed changes, but long-chain polyunsaturated fatty acids, which are minor components of bile, were shown to be incorporated into phospholipids of V. cholerae. Although the bile-induced phospholipid profile was independent of the V. cholerae virulence cascade, we identified another relevant environment in which V. cholerae assimilates unique fatty acids into its membrane phospholipids - marine sediment. Our results suggest that Vibrio species possess unique machinery conferring the ability to take up a wider range of exogenous fatty acids than other enteric bacteria.

Immunological efficacy of glycoconjugates derived from Vibrio cholerae O1 serotype Ogawa detoxified LPS in mice

This study focused on changes in selected parameters of humoral and cellular immunity following vaccination of mice with unique Vibrio cholerae LPS–protein-complexed conjugates. The V. cholerae detoxified LPS (dLPS)-derived antigenic structures O-specific polysaccharide (O-SP) and de-O-acylated LPS (DeOAc-LPS) were used to prepare glycoconjugates by linking both dLPSs to glucan, the immunomodulating matrix, and then to BSA carrier. Animals were given a primary vaccination and boosted at 2-week intervals with a dose of 4.5 μg saccharide antigen. The last boost was given either subcutaneously or intraperitoneally (i.p.) to compare the boosting effect and to optimize the effective immunization route. Both conjugates (O-SP–BSA and DeOAc-LPS–BSA) induced significant levels of antigen-specific Ig isotypes, especially IgG and IgM. The i.p. booster route was more effective. A T helper 1 response was achieved only by immunization with O-SP–BSA conjugate administered i.p. Significant acceleration of phagocytic capacity and respiratory burst of neutrophils was demonstrated by both immunogenic formulations. Activation of T- and B-cell adaptive immunities was exhibited as specific changes in CD3 : CD19 and CD4 : CD8 ratios, B-cell low-affinity Fcγ II and III receptor expression and induction of CD45R antigen.