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Biomedical subjects

A L Cheung

Publications and source records attributed to A L Cheung.

63 records · Page 4Linked to original sources
PubMed1989

Protective efficacy of protein A-specific antibody against bacteremic infection due to Staphylococcus aureus in an infant rat model.

Staphylococcal protein A (SpA) is a potent antiphagocytic component of the cell wall of most pathogenic Staphylococcus aureus strains. We studied the in vitro opsonophagocytic and in vivo protective activities of rabbit immunoglobulin G (IgG) antibody to purified SpA obtained from two unencapsulated S. aureus strains (Cowan I and 17A). Postimmune serum contained high titers of specific IgG to SpA, as measured by a modified enzyme-linked immunosorbent assay that blocked nonspecific binding of IgG to SpA. In vitro, both S. aureus strains were efficiently phagocytosed and killed by polymorphonuclear leukocytes in the presence of nonimmune sera and complement. With one strain (Cowan I), opsonophagocytosis was significantly enhanced in the presence of SpA antibody, but with the other strain (17A), killing was significantly decreased with immune serum. We then evaluated the potential protective benefit of SpA antibody in preventing S. aureus bacteremia in infant rats. Two-day-old rats received saline or various doses of SpA antiserum and were challenged subcutaneously 1 day later, but even the highest levels of antibody did not significantly reduce mortality, bacteremia or metastatic infection to lungs or liver (frequency or magnitude). This lack of protective efficacy was not related to a failure of SpA F(ab')2 to bind to cell surface-exposed epitopes, since F(ab')2 fragments prepared from hyperimmune serum bound avidly to the whole organism in an enzyme-linked immunosorbent assay.

Animals↗
PubMed1989

Role of surface proteins in staphylococcal adherence to fibers in vitro.

To study the role of surface proteins in the adherence of Staphylococcus aureus to fibers that are used in tampon and surgical gauze pad manufacture, we have developed an adherence assay with S. aureus cells and cotton and rayon fibers. Results suggest that staphylococcal adherence is dependent on both the substrate and the material used to coat these fibers. Scanning electron micrographs supported the adherence results and revealed more cells on the surface of cotton than rayon fibers. Treatment of staphylococcal cells with proteolytic enzymes significantly reduced binding to pure cotton and detergent-treated cotton fibers. Immunoblot analysis of cell wall proteins suggested that surface proteins in the mol wt range of 120-220 kD were involved in the adherence of S. aureus to cotton fibers. Although the adherence of S. aureus to cotton fibers alone appeared to be mediated through surface charge or hydrophobic interactions, bacterial binding to fibers which have been pretreated with defibrinated blood appeared to be more specific and independent of the surface constituents of the fibers. The results of these studies implicate staphylococcal surface proteins in the adherence of S. aureus to commercially available tampon fibers and surgical gauze pads.

Animals↗
PubMed1988

Variation in the expression of cell wall proteins of Staphylococcus aureus grown on solid and liquid media.

To evaluate the variation in the expression of cell wall antigens between Staphylococcus aureus grown in liquid medium and solid support, bacteria were harvested from liquid chemically defined medium and chemically defined medium in a 1% agar base. Cell wall proteins were then extracted by lysostaphin in a protoplast-stabilizing medium (30% raffinose). After separation of the cell wall antigens by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western blots, they were probed with chicken antiserum to an S. aureus strain grown on a solid support. For each of the 15 clinical strains analyzed, high-molecular-size bands (molecular size range, 120 to 220 kilodaltons) were either enhanced or distinctly present when compared with those from the cell wall extract of the same strain grown in liquid medium. Results of enzymatic treatment of whole staphylococci grown on solid medium suggested the proteinaceous nature and the surface location of these antigens. Limited passage studies demonstrated the ability of the staphylococci to alter these surface proteins when passaged alternately on liquid and solid media. These observations suggested the importance of the microenvironment to the expression of cell wall proteins in S. aureus. Correlations with observations in vivo may help identify the determinants of microbial pathogenicity in S. aureus.

Antigens, Bacterial↗
PubMed1987

Analysis by gel electrophoresis, Western blot, and peptide mapping of protein A heterogeneity in Staphylococcus aureus strains.

To evaluate potential differences in protein A among Staphylococcus aureus strains, lysostaphin-solubilized cell wall proteins from 12 serologically distinct strains were analyzed by 7.5% sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis (PAGE). Seven presumptive protein A variant identified in the 45- to 57-kilodalton range were then studied for qualitative binding affinities to nonimmune mouse and rabbit immunoglobulin G (IgG) by enzyme-linked immunoelectrotransfer blot. Essentially, all presumptive protein A variants demonstrated binding to both nonimmune rabbit and mouse IgG and had differential binding to mouse monoclonal IgG1 at pH 8.2 than at 5.5. Because of Fc-binding properties and molecular weight similarity to the well-characterized Cowan I protein A, these proteins appeared to represent protein A variants. Amino sugar analysis (less than 1%) by reverse-phase high-pressure liquid chromatography suggested that the apparent molecular weight differences in protein A were not due to associated mucopeptides. Further differences in protein A variants were studied by peptide mapping. Each of the seven protein A variants, distinguishable on SDS-PAGE, also produced distinct peptide cleavage patterns. In addition, two protein A variants indistinguishable on SDS-PAGE could be further subdivided by peptide mapping. These results suggest that SDS-PAGE analysis of protein A, particularly in conjunction with peptide mapping, may be useful in distinguishing distinct strains of S. aureus. Different protein A variants may also have unique functional or immunologic capabilities.

Bacterial Proteins↗
PubMedDate not supplied

Surface proteins of Staphylococcus aureus.

Crude cell walls of Staphylococcus aureus of potential immunologic or epidemiologic importance were prepared for study by mechanically disrupting whole cells and applying differential centrifugation. Cell-wall proteins were then released from the wall by lysostaphin digestion and analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Distinct electrophoretic protein patterns were found for each of the 12 serologically distinct strains examined. There were two major groups of cell-wall proteins identified in the 45-57-kilodalton (kdal) and 100-190-kdal range, respectively. Proteins in the 45-57-kdal range appeared to represent protein A variants of different apparent molecular mass. Localization experiments with 125I labeling demonstrated the surface location of most of the proteins. These data suggest that selected surface-exposed proteins may be important in defining host immune responses to S. aureus infections.

Autoradiography↗