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Biomedical subjects

X Q Meng

Publications and source records attributed to X Q Meng.

At least 19 recordsLinked to original sources
PubMed1994

Haemagglutination activity of toxigenic and non-toxigenic strains of Clostridium difficile.

Cell extract of Clostridium difficile strains was fractionated by ammonium sulfate precipitation and sulfated cellulofine column chromatography to detect haemagglutination (HA) activity. HA activity without cytotoxicity was detected in fractions eluted at 0.79-0.91 M NaCl in sulfated cellulofine column chromatography of the cell extract in both toxigenic strain VPI 10463 and non-toxigenic strain KZ 1678, while toxin A was detected in fractions eluted at 0.27-0.29 M NaCl. Antisera were prepared with HA substance-containing fractions of the chromatography. Antiserum to the HA substance(s) of strain VPI 10463 neutralised the HA activity of the fractions of strains VPI 10463 and KZ 1678 at nearly the same titres. Antiserum to the HA substance(s) of strain KZ 1678 also neutralised the HA activity of both strains at nearly the same titres as above. These findings suggest that haemagglutinin(s) is commonly produced by C. difficile strains irrespective of toxin A-producing ability.

Animals↗
PubMed1994

Toxin production by Clostridium difficile in a defined medium with limited amino acids.

Basal defined medium (BDM) containing vitamins, minerals and seven amino acids--(/L) tryptophan 0.1 g, methionine 0.2 g, valine 0.3 g, isoleucine 0.3 g, proline 0.3 g, leucine 0.4 g and cysteine 0.5 g--which appeared to be essential for good growth of Clostridium difficile was prepared. Addition of glycine 0.2 g/L and threonine 0.4 g/L to BDM produced better growth of strain VPI 10463, and this defined medium was designated minimum amino acid-defined medium (MADM). Production of toxins A and B by strain VPI 10463 in 6 x MADM containing (/L) tryptophan 0.6 g, methionine 1.2 g, valine 1.8 g, isoleucine 1.8 g, proline 1.8 g, leucine 2.4 g, cysteine 0.5 g, glycine 0.2 g and threonine 0.4 g, was much greater than in MADM. Toxin production by 20 C. difficile strains was examined in two defined media--6 x MADM and complete amino acid-defined medium (CADM) containing 18 amino acids--and one complex medium, modified brain heart infusion medium (m-BHI). Simultaneous production of toxins A and B by all test strains was demonstrated in m-BHI and the two defined media. It was also shown that 6 x MADM was generally better than CADM and as effective as m-BHI for stimulating toxin production by 13 strains. This defined medium would be useful for studies on the physiology, metabolism and pathogenicity of C. difficile.

Amino Acids↗
PubMed1993

Purification and characterisation of intracellular toxin A of Clostridium difficile.

After sonic disintegration of Clostridium difficile cells, intracellular toxin A was purified to homogeneity by thyroglobulin affinity chromatography (TGAC) followed by anion-exchange (Mono Q) by fast protein liquid chromatography (FPLC). High haemagglutinating (HA) activity was detected in TGAC-unbound fractions (2(9)/50 microliters), but not in TGAC thermal eluates (2(0)/50 microliters). The low HA titre of the thermal eluates was markedly increased to 2(5)/50 microliters after dialysis against 0.02 M Tris-HCl (pH 7.5). A disparity in the position of the peaks containing cytotoxic and HA activity was observed in the first Mono Q-FPLC step. Intracellular toxin A without HA activity was obtained by a second Mono Q-FPLC step. The M(r) of the intracellular toxin A was estimated by polyacrylamide gel electrophoresis (PAGE) to be 580 kDa under non-denaturing conditions. The minimum doses of the toxin causing cytotoxicity, mouse lethality and enterotoxicity were 0.83 ng, 8.7 ng and 5 micrograms, respectively.

Animals↗
PubMed1993

Immunological comparison of intracellular toxin A and extracellular toxin A from Clostridium difficile.

Intracellular toxin A and extracellular toxin A of Clostridium difficile were compared immunologically. Immunodiffusion tests with anti-intracellular toxin A and anti-extracellular toxin A sera showed that these toxins were identical. In neutralization tests, both antisera neutralized the homologous and heterologous toxins with regard to cytotoxicity, mouse lethality and loop response at nearly the same titers. Although intracellular toxin A lacks the hemagglutination (HA) activity, anti-intracellular toxin A serum neutralized HA activity of extracellular toxin A at the same titer as did anti-extracellular toxin A serum. These results suggest that these toxins are immunologically indistinguishable and that the intracellular toxin A molecule has an antigenic site(s) for the HA activity.

Animals↗
PubMed1992

Correlation between cytotoxin production and sporulation in Clostridium difficile.

Correlation between cytotoxin production and sporulation was demonstrated when a Clostridium difficile culture was inoculated into fresh broth to give an initial count of less than 10 vegetative cells/ml with no spores. Under these conditions, cytotoxin was produced and released during sporulation. Addition of a sporulation inhibitor (acridine orange, 30 mg/L), resulted in a marked decrease in both sporulation and cytotoxin production, despite there being no change in the number of vegetative cells in the culture. These results indicate that sporulation might be closely related to cytotoxin production.

Acridine Orange↗
PubMed1991

Production of monoclonal antibody to Clostridium difficile toxin A which neutralizes enterotoxicity but not haemagglutination activity.

Nine monoclonal antibodies (mAb) to Clostridium difficile toxin A were produced. The isotype of one mAb (37B5) was IgG2b, kappa, and that of the other eight mAbs was IgM, kappa. Immunoblot analysis after non-denatured PAGE showed that with the exception of one mAb (112G6) all mAbs gave a positive reaction with the 540 kDa band of toxin A. Immunoblot analysis showed that four mAbs (2E15, 3B4, 37B5 and 49C4) gave a positive reaction with the 240 kDa major band of toxin A. In neutralisation tests with these mAbs for enterotoxicity, mouse lethality, haemagglutination activity and cytotoxicity, 37B5 neutralised enterotoxicity in a rabbit ileal loop response test but did not neutralise any other biological activities. None of the other eight mAbs showed any neutralising activities at all.

Animals↗
PubMed1991

[Freeze-etch study on the brush border structure of Cysticercus cellulosae].

The images of C. cellulosae detected by freeze-itch technique were exactly similar to those observed in the thin section. The scolex microtriches might be divided into two parts, a thick proximal portion and a thinner spinal distal end, the former measuring about 0.2-0.4 micron in length, the latter measuring about 1-2 microns in length. On the extracellular surface of the proximal portion of microthrix, 1 or 2 particles could occasionally be seen, while numerous particles appeared on the protoplasmic fracture face (PF face) of the proximal portion. The PF face were closely packed and irregularly distributed with membranous particles, which were spherical or subspherical in shape, measured 0.01-0.02 micron in diameter. The extracellular fracture face (EF face), of proximal portion and all four membranous faces of spinal end were smooth. The tegumentary plasmic membrane was 0.02 micron in thickness, with smooth ES face. The PF face of this membrane packed closely with numerous particles, which were similar with those on the PF face of the microthrix. Numerous globular or discoidal vesicles scattered at random in the tegumentary matrix. Most mitochondria were near the basement membrane of the matrix. In the parenchymal layer, the parenchymal cells, calcareous corpuscles and flame-cells could easily be seen. Most of the calcareous corpuscles and flame-cells were located closely beneath the muscle layer. The flame-cell of C. cellulosae mainly consisted of three portions, cell body, a bundle of cilia and a filtered cell lumen. The flame-cell body had a large nucleus and relatively few cytoplasm with several mitochondria.(ABSTRACT TRUNCATED AT 250 WORDS)

Actin Cytoskeleton↗
PubMed1986

The operculum-plug area and membranous structure of the eggs of Trichuris trichiura.

Eggs of Trichuris trichiura were prepared for scanning electron microscopy (SEM) by the dimethylsulfoxide freeze-cracking method. The egg-shell and oocyte were examined by SEM. The egg has a chitinous shell which consists of more than 10 layers of dense lamellae. The shell is bordered by a limiting membrane. An operculum and a collar made of chitinous shell together form the opercular area. The operculum is an empty cavity. The chitinous fibers of the egg-shell in this area are diffuse and loose, with numerous micropores or spaces. The egg-shell in this area therefore appears to form a fine tubular network. The oocyte is an undifferentiated cell with a biconcave drum-like shape. The perivitelline space is conspicuous at both ends of the cell.

Animals↗