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At least 199 records · Page 11Linked to original sources
PubMed1990

Visualization of the bacterial polysaccharide capsule.

The highly hydrated capsule of E. coli strains is composed of a large number of polysaccharide fibers of which the thinnest measure about 2 nm in width. The fibers may span the entire distance from the outer membrane to the outer rim of the capsule and show a propensity to associate with each other to form thicker filaments. Presence of thick filaments may also indicate a partial collapse of the capsular organization due to removal of water. The in vivo capsule represents a relatively open structure with the negatively charged polysaccharide fibers permitting the binding of large quantities of water and ions, and providing intracellular space for diffusing molecules to access the envelope membranes even in conditions of high cell density. Negative charge and steric hindrance of the polysaccharide strands protect the cells against attack by a large variety of harmful macromolecules and against infection by most bacteriophages. Two types of procedure have been most successful in maintaining the size and overall structure of the capsule: (a) the interaction of cationic molecules with the in vivo capsule, and (b) the use of antibody to stabilize capsules for subsequent dehydration and plastic embedding. A further type of potentially useful procedure, cryofixation and cryosubstitution, has shown interesting results in a number of cases. These techniques are expected to play a significant role in structural studies in the near future. The sites of export of capsular antigen have been described in earlier conventional electron microscopic studies. Data obtained from the recent technique of "on-section" labeling support the model that both the capsular antigen and the O antigen are assembled at junctions of the inner and outer membrane. It is anticipated that one will be able to discern in greater ultrastructural detail the membranes at which the antigen is translocated. Novel membrane fixation and isolation techniques will have to be established and employed in a combination of sensitive microscopic techniques and immuno- and enzyme localization methods. These developments will make it possible to explore questions pertaining to the maintenance and structural organization of microbial capsules and the functional interaction of polysaccharides with natural surfaces, man-made substances and drugs.

Antigens, Bacterial↗
PubMed1990

Neisseria meningitidis group B capsular polysaccharide. Bacterial content and release in relation to categories of infection and filtrability of released endotoxin.

A total of 41 Neissera meningitidis isolates were analyzed for capsular polysaccharide (CP) and lipopolysaccharide (LPS) release and filtrability. Twenty-two of these isolates were serogroup B from blood or cerebrospinal fluid of patients, five were group B isolates from healthy throat carriers, and 14 were nongroupable (acapsular) meningococcal isolates from healthy carriers. Filtration of liquid whole-cell cultures through cellulose acetate-nitrate filters resulted in distinctly lower LPS filtrate activity for acapsular than for capsular meningococci (p less than 0.001). On the other hand, when polysulfone membrane filtration was performed, filtrates from acapsular and capsular meningococci contained LPS in similar amounts. These results indicate that LPS-containing particles released from acapsular isolates are larger or more aggregated than corresponding CP- and LPS-containing particles released from capsular isolates. The LPS released from acapsular isolates apparently are more efficiently retained by adsorption to cellulose acetate-nitrate. From the capsular isolates comparatively more CP than LPS appeared to be released, as related to cell-bound amounts. The total amounts of CP and released, filtrable LPS through cellulose acetate-nitrate filters were both relatively low and had similar values for capsular carrier meningococci and systemic isolates from mild meningococcal disease. The amount of CP released and passing this type of membrane was significantly higher for systemic isolates from severe septicemia than from mild meningococcal disease (p = 0.03).

Enzyme-Linked Immunosorbent Assay↗
PubMed1992

T cell regulation of the antibody response to bacterial polysaccharide antigens: an examination of some general characteristics and their implications.

The characteristics of thymus-derived (T) lymphocytes that regulate the magnitude of the antibody response to the capsular polysaccharide antigen of type III Streptococcus pneumoniae are considered within the context of a general homeostatic model for controlling the antibody response to microbial antigens of medical importance. Some experimental approaches are described in which the activities of such regulatory T cells are modulated to provide an increase in the development of host immunity, to improve the immunogenicity of poorly immunogenic antigens, or to eliminate the inhibitory effects of suppressor T cells.

Animals↗
PubMed1991

Control of components of bacterial polysaccharide vaccines by physical methods.

Analysis of polysaccharide components of meningococcal- and pneumococcal vaccines was carried out by proton n.m.r. spectroscopy and gas chromatography. The meningococcal polysaccharides were of high purity but showed differences in degree and position of O-acetylation between manufacturers. The level of contamination of the pneumococcal polysaccharides by C-substance was quantified. These methods provide an alternative to immunological methods for determining serotype and purity.

Bacterial Vaccines↗
PubMed1993

Genetic organization and sequence of the rfb gene cluster of Yersinia enterocolitica serotype O:3: similarities to the dTDP-L-rhamnose biosynthesis pathway of Salmonella and to the bacterial polysaccharide transport systems.

The Yersinia enterocolitica O:3 lipopolysaccharide O-antigen is a homopolymer of 6-deoxy-L-altrose. The cloned rfb region was sequenced, and 10 open reading frames were identified. Transposon mutagenesis, deletion analysis and transcomplementation experiments showed that eight of the genes, organized into two operons, rfbABC and rfbDEFGH, are essential for O-antigen synthesis. Functional tandem promoters were identified upstream of both operons. Of the deduced polypeptides RfbA, RfbF and RfbG were similar to Salmonella proteins involved in the dTDP-L-rhamnose biosynthesis. Rhamnose and 6-deoxy-L-altrose are C3-epimers suggesting that analogous pathways function in their biosynthesis. RfbD and RfbE were similar to capsular polysaccharide export proteins, e.g. KpsM and KpsT of Escherichia coli. This and transposon mutagenesis showed that RfbD and RfbE function as O-antigen exporters.

Amino Acid Sequence↗