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At least 19 recordsLinked to original sources
PubMed1986

Cloning part of the region encoding biosynthetic enzymes for surface antigen (O-antigen) of Salmonella typhimurium.

The rfb gene cluster of Salmonella typhimurium encodes the enzymes required for the biosynthesis of the O-Antigen. A part of it has been cloned in plasmid vectors pBR322 and pUC9 using an adjacent, previously cloned, part of the his operon (Barnes 1981) as a molecular probe for the first clone. A detailed restriction enzyme map of 7.57 kb of rfb DNA is presented and the approximate locations of two of the genes, rfbK and rfbM have been defined.

Antigens, Bacterial↗
PubMed2004

Lipopolysaccharide O antigen status of Yersinia enterocolitica O:8 is essential for virulence and absence of O antigen affects the expression of other Yersinia virulence factors.

Lipopolysaccharide (LPS) is the major component of the outer membrane of Gram-negative bacteria. Although much attention has been given to the biological effects of its lipid A portion, a great body of evidence indicates that its O chain polysaccharide (O antigen) portion plays an important role in the bacterium-host interplay. In this work we have studied in-depth the role of the O antigen in Yersinia enterocolitica serotype O:8 pathogenesis. We made a detailed virulence analysis of three mutants having different O antigen phenotypes: (i) LPS with no O antigen (rough mutant); (ii) LPS with one O unit (semirough mutant) and (iii) LPS with random distribution of O antigen chain lengths. We demonstrated that these LPS O antigen mutants were attenuated in virulence regardless of the infection route used. Co-infection experiments revealed that the rough and semirough mutants were severely impaired in their ability to colonize the Peyer's patches and in contrast to the wild-type strain they did not colonize spleen and liver. The mutant with random distribution of O antigen chain lengths, however, survived better but started to be cleared from mouse organs after 8 days. As an explanation to this attenuation we present here evidence that other Yersinia virulence factors depend on the presence of O antigen for their proper function and/or expression. We demonstrated that in the rough mutant: (i) the YadA function but not its expression was altered; (ii) Ail was not expressed and (iii) inv expression was downregulated. On the other hand, expression of flhDC, the flagellar master regulatory operon, was upregulated in this mutant with a concomitant increase in the production of flagellins. Finally, expression of yplA, encoding for the Yersinia phospholipase A, was also upregulated accompanied by an increased flagellar type III secretion system mediated secretion of YplA to culture medium. Together these findings suggest that the absence of O antigen in the outer membrane of Yersinia either directly or indirectly, for example through a cellular or membrane stress, could act as a regulatory signal.

Adhesins, Bacterial↗
PubMed1980

Immunochemistry of Salmonella O-antigens: specificity of rabbit antibodies against the O-antigen 2 determinant elicited by whole bacteria and 3-O-alpha-paratopyranosyl-D-mannopyranosyl conjugated to bovine serum albumin.

The binding specificities of antibodies directed against the Salmonella sero-group A-specific O-antigen 2 determinant were characterized by precipitation-inhibition and enzyme-linked immunosorbent assay inhibition tests. Two different antigen O-2-specific antisera were investigated: one conventional factor O-2 serum (elicited by whole heat-killed Salmonella paratyphi A bacteria) and another elicited by the synthetic disaccharide 3-O-a-paratopyranosyl-D-mannopyranosyl (formula: see text) covalently linked via a p-isothiocyanatophenyl aglycon to bovine serum albumin (PM-BSA). The inhibition data showed that factor O-2 antibodies have combining sites which recognize structures larger than the (formula: see text) disaccharide and equal to or smaller than an O-antigen O-2-specific octasaccharide derived from the S. paratyphi A O-polysaccharide. Although the factor O-2 serum exhibited a high specificity for the homologous S. paratyphi A O-antigen it still precipitated, though weakly, a heterologous Salmonella typhimurium O-antigen. In contrast, anti-PM-BSA antibodies were exclusively specific for the O-2 determinant of the native polysaccharide antigen. The combining sites of these antibodies best recognized the (formula: see text) disaccharide, including the linkage arm and the lysyl residue of the BSA carrier protein molecule. These data extend earlier findings as to the superior specificity of anti-PM-BSA antibodies as compared to conventional factor O-2 antibodies.

Animals↗
PubMed1998

Escherichia coli clone Sonnei (Shigella sonnei) had a chromosomal O-antigen gene cluster prior to gaining its current plasmid-borne O-antigen genes.

O antigen is part of the lipopolysaccharide present in the outer membrane of gram-negative bacteria. The surface-exposed O antigen is subject to selection by the host immune system, which may account for the maintenance of many different O-antigen forms. Characteristically, all genes specific to O-antigen synthesis are clustered in a region close to the his and gnd genes on the chromosome of Escherichia coli and related species. Shigella sonnei, essentially a clone of E. coli (E. coli clone Sonnei), is an important human pathogen and is unusual in that its O-antigen gene cluster is located on a plasmid. Our results suggest that it once had a normal chromosomal O-antigen gene cluster which has been largely deleted. We suggest that the O antigen encoded by the plasmid-borne genes offered a selective advantage in adapting to a new environment and that the chromosomal O-antigen genes were eventually inactivated. We also identified, by PCR and sequencing, a potential ancestor of E. coli Sonnei among the 166 known E. coli serotype strains.

Bacterial Proteins↗
PubMed1981

Serotyping of Serratia marcescens: confirmation of five recently described new O-antigens and characterization of an additional O-antigen.

Five new Serratia marcescens O-antigens (O16--O20) of Le Minor and Pigache were confirmed. An additional O-antigens (O21) was found and characterized. All six O-antigens cross-reacted with previously established O-antigens of S. marcescens, necessitating the employment of cross-absorbed rabbit anti-O immune sera for definitive O-antigen analyses.

Agglutination Tests↗
PubMed1982

[Partial composition of the O-antigens of O-group Escherichia].

The partial composition of O-antigens in Escherichia known as the causative agents of escherichioses localized in the intestine and other organs has been studied. Escherichia of groups 01, 02 and 03 are characterized by different partial composition of their O-antigens. This composition can be expressed by the formulae: 01a, 1b; 01a, 1b, 1c; 01a, 1b, 1c, 1d; 01a, 1e; 02a, 2b, 2c; 02a, 2b, 2c, 2d, 2e; 02a, 2b, 2d, 2e, 2g; 02a, 2c, 2e; 06a, 6b; 06a, 6c. No pronounced correlation between the partial composition of O-antigens within the O-group and the presence of different K- or H-antigens in the strain has been established. The scheme of adsorption has been developed and anti-Escherichia factor O-sera have been obtained. The use of these sera allows one to differentiate Escherichia strains, isolated from patients, within the O-groups according to the partial composition of their antigens, which is of both diagnostic and epidemiological importance.

Adsorption↗
PubMed1975

Interactions between the immunological responses of a thymus-independent antigen (Salmonella adelaide O antigen) with a thymus-dependent antigen (sheep erythrocytes) in the adult bird.

The bird's antibody response to a thymus-dependent antigen (sheep erythrocytes) (SRBC) and a thymus-independent antigen (SALMONELLA ADELAIDE O antigen) were characterized: whereas the former proceeded through a brief 19S response to a declining 7S response, the latter failed to switch from 19S TO 7S for several weeks and consisted in repeated excursions of 19S antibodies. When injected intravenously and simultaneously an injection of S. adelaide-killed organisms and SRBC interact, so that the response to the latter fails to switch from 19S TO 7S and consists of repeated excursions of 19S antibodies. The changed character of the SRBC response is interpreted to be due to the relative lack of 7S antibody: passive 7S antibody to S. adelaide O antigen or 7S anti-SRBC produces a negative feedback inhibition of their respective responses, so that only one excursion of 19S antibody is observed. The effect is not, however, symmetrical; the thymus-independent antigen is dominant. Thus, whereas 7S antibody to S. adelaide produces the same negative feedback inhibition on the response to S. adelaide and the response to SRBC (when injected with adlaide), 7S antibody to SRBC inhibits only the response to SRBC and not the response to S. adelaide. These results are discussed relation to current hypotheses of antibody biosynthesis and mechanisms of adjuvant action. They are also discussed in relation to the function of the germinal centres of the spleen which may function to mediate the negative feedback of 7S antibody on the antibody response.

Adjuvants, Immunologic↗
PubMed1978

Citrobacter O-antigens: structure of the O-antigenic polysaccharide from Citrobacter sp. 396.

The structure of the O-specific polysaccharide moiety of the lipopolysaccharide from Citrobacter 396 was elucidated by composition, methylation, and periodate oxidation studies. The repeating unit consists of four 2-linked mannoses and one 3-linked N-acetylglucosamine. One of the mannose units is substituted at C3 with alpha-glucose, and one is substituted at C3 with alpha-(2-O-acetyl)-abequose. All the mannosyl linkages appear to have the beta-configuration; the N-acetylglucosaminyl linkage has the alpha-configuration. In bacterial agglutination and passive hemagglutination in some Salmonella antisera, Citrobacter 396 as well as its O-antigenic lipopolysaccharide expressed the serological factors 5 and 6. In corroboration of our structural studies, this showed the presence of alpha-(2-O-acetyl)-abequosyl-1,3-mannose (factor 5) and alpha-glucosyl-1,3-mannose (factor 6).

Antigens, Bacterial↗
PubMed2003

Actinobacillus actinomycetemcomitans serotype d-specific antigen contains the O antigen of lipopolysaccharide.

Actinobacillus actinomycetemcomitans is a gram-negative, facultatively anaerobic bacterium which is associated especially with aggressive forms of periodontitis. Contradictory results on the localization of the A. actinomycetemcomitans serotype-specific antigen have been reported. The aim of the present study was to characterize the A. actinomycetemcomitans serotype d-specific antigen. The antigen was isolated by affinity chromatography. The affinity column was prepared from immunoglobulin G isolated from rabbit antiserum raised against A. actinomycetemcomitans serotype d. The isolated antigen was analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, Western blotting, and silver staining, all of which revealed a ladder-like structure typical for the O antigen of lipopolysaccharide (LPS). In a displacement enzyme-linked immunosorbent assay (ELISA), the isolated antigen displaced in a concentration-dependent manner the binding of the polyclonal rabbit antiserum raised against A. actinomycetemcomitans serotype d to the competing whole-cell serotype d antigen. The isolated antigen contained LPS, and an equal concentration of LPS isolated from A. actinomycetemcomitans serotype d gave a similar displacement curve in the ELISA. In order to test the immunogenic properties of the isolated antigen, it was used to immunize a rabbit. The antiserum raised against the isolated antigen displayed specificity in Western blotting and ELISA similar to that of antibody raised against LPS isolated from A. actinomycetemcomitans serotype d. In conclusion, our results show that the A. actinomycetemcomitans serotype d-specific antigen contains the O-antigenic structure of LPS.

Actinobacillus Infections↗
PubMed2003

Biosynthesis of O-antigens: genes and pathways involved in nucleotide sugar precursor synthesis and O-antigen assembly.

The O-antigen is an important component of the outer membrane of Gram-negative bacteria. It is a repeat unit polysaccharide and consists of a number of repeats of an oligosaccharide, the O-unit, which generally has between two and six sugar residues. O-Antigens are extremely variable, the variation lying in the nature, order and linkage of the different sugars within the polysaccharide. The genes involved in O-antigen biosynthesis are generally found on the chromosome as an O-antigen gene cluster, and the structural variation of O-antigens is mirrored by genetic variation seen in these clusters. The genes within the cluster fall into three major groups. The first group is involved in nucleotide sugar biosynthesis. These genes are often found together in the cluster and have a high level of identity. The genes coding for a significant number of nucleotide sugar biosynthesis pathways have been identified and these pathways seem to be conserved in different O-antigen clusters and across a wide range of species. The second group, the glycosyl transferases, is involved in sugar transfer. They are often dispersed throughout the cluster and have low levels of similarity. The third group is the O-antigen processing genes. This review is a summary of the current knowledge on these three groups of genes that comprise the O-antigen gene clusters, focusing on the most extensively studied E. coli and S. enterica gene clusters.

Carbohydrate Sequence↗
PubMed2003

Characterization of the O antigen gene cluster and structural analysis of the O antigen of Francisella tularensis subsp. tularensis.

A gene cluster encoding enzymes involved in LPS O antigen biosynthesis was identified from the partial genome sequence of Francisella tularensis subsp. tularensis Schu S4. All of the genes within the cluster were assigned putative functions based on sequence similarity with genes from O antigen biosynthetic clusters from other bacteria. Ten pairs of overlapping primers were designed to amplify the O antigen biosynthetic cluster by PCR from nine strains of F. tularensis. Although the gene cluster was present in all strains, there was a size difference in one of the PCR products between subsp. tularensis strains and subsp. holarctica strains. LPS was purified from F. tularensis subsp. tularensis Schu S4 and the O antigen was shown by mass spectrometry to have a structure similar to that of F. tularensis subsp. holarctica strain 15. When LPS from F. tularensis subsp. tularensis Schu S4 was used to immunize mice that were then challenged with F. tularensis subsp. tularensis Schu S4, an extended time to death was observed.

Animals↗