Biomedical subjects

A S Ho

Publications and source records attributed to A S Ho.

24 records · Page 2Linked to original sources

PubMed1993

Characterization of fimbriae produced by enteropathogenic Escherichia coli.

Enteropathogenic Escherichia coli (EPEC) express rope-like bundles of filaments, termed bundle-forming pili (BFP) (J. A. Girón, A. S. Y. Ho, and G. K. Schoolnik, Science 254:710-713, 1991). Expression of BFP is associated with localized adherence to HEp-2 cells and the presence of the EPEC adherence factor plasmid. In this study, we describe the identification of rod-like fimbriae and fibrillae expressed simultaneously on the bacterial surface of three prototype EPEC strains. Upon fimbrial extraction from EPEC B171 (O111:NM), three fimbrial subunits with masses of 16.5, 15.5, and 14.7 kDa were separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Their N-terminal amino acid sequence showed homology with F9 and F7(2) fimbriae of uropathogenic E. coli and F1845 of diffuse-adhering E. coli, respectively. The mixture of fimbrial subunits (called FB171) exhibited mannose-resistant agglutination of human erythrocytes only, and this activity was not inhibited by alpha-D-Gal(1-4)-beta-Gal disaccharide or any other described receptor analogs for P, S, F, M, G, and Dr hemagglutinins of uropathogenic E. coli, which suggests a different receptor specificity. Hemagglutination was inhibited by extracellular matrix glycoproteins, i.e., collagen type IV, laminin, and fibronectin, and to a lesser extent by gangliosides, fetuin, and asialofetuin. Scanning electron microscopic studies performed on clusters of bacteria adhering to HEp-2 cells revealed the presence of structures resembling BFP and rod-like fimbriae linking bacteria to bacteria and bacteria to the eukaryotic cell membrane. We suggest a role of these surface appendages in the interaction of EPEC with eukaryotic cells as well as in the overall pathogenesis of intestinal disease caused by EPEC.

ABO Blood-Group System↗

PubMed1992

Cloning and characterization of fxp, the flexible pilin gene of Aeromonas hydrophila.

The flexible pilus of Aeromonas hydrophila is a morphologically and biochemically unique organelle which binds eukaryotic cell surfaces and whose expression is induced by specific physiochemical conditions. fxp, the structural gene coding for the flexible pilus subunit, was localized on a 7.6kb plasmid of A. hydrophila strain AH26. A putative Shine-Dalgarno sequence and -10 and -35 regions were identified, a signal peptide sequence delineated, and the coding sequence compared with other bacterial sequences and found to be unique. Plasmid and chromosomal DNA was prepared from 66 other Aeromonas strains and 12 strains from other bacterial genera and examined by Southern blot hybridization using a labelled fxp oligonucleotide and the 7.6kb plasmid as probes. No hybridizing sequences were identified except in the original strain, AH26. It is proposed that fxp codes for a highly evolved organelle, possibly widely distributed in nature, but that it is carried on a genetic element that is rapidly lost from most strains upon in vitro cultivation and storage.

Aeromonas hydrophila↗

PubMed1991

An inducible bundle-forming pilus of enteropathogenic Escherichia coli.

Enteropathogenic Escherichia coli (EPEC), a cause of childhood diarrhea, grow on the surface of the small intestine and on cultured epithelial cells as colonies of adherent bacteria. When propagated on solid medium containing blood or attached to HEp-2 cells, EPEC express ropelike bundles of filaments, termed bundle-forming pili (BFP), that create a network of fibers that bind together the individual organisms. BFP were found to be expressed by five EPEC serogroups, each harboring a approximately 92-kilobase plasmid previously known to be important for virulence in humans. When two of these strains were cured of this plasmid, they neither expressed BFP nor grew as adherent colonies. An antiserum to BFP reduced the capacity of EPEC to infect cultured epithelial cells. BFP are composed of a repeating subunit of 19,500 daltons, the amino-terminal amino acid sequence of this subunit is homologous to that of the toxin-coregulated pilin of Vibrio cholerae.

Amino Acid Sequence↗

PubMed1991

Recent evolutionary history of the metallothionein gene Mtn in Drosophila.

A new allele of one of the metallothionein genes of D. melanogaster, Mtn.3, sheds light on the recent evolution of this gene. In comparison to the previously studied Mtn1 allele found in Canton S, this new allele, Mtn.3, produces a transcript that is 49 bases longer and 65-70% less abundant. We detected Mtn.3 in several laboratory strains as well as in isofemale lines derived from natural populations. Sequence comparison showed that Mtn.3 differs from Mtn1 in that it has: (a) base-pair substitution and an extra 49 bp-segment in the 3' untranslated region, (b) a substitution in the coding region that replaces the terminal Glu40 in Mtn1 with Lys40, and (c) two base-pair substitutions in the promoter region. The Mtn.3-type was detected in six species of the melanogaster group by restriction analysis, and this result was confirmed by sequencing the D. simulans Mtn gene. Thus Mtn.3, which produces a less abundant transcript, appears to be the oldest of the two alleles. We also found that the duplications previously isolated from natural populations all derived from Mtn1, the more recent allele. Thus, two evolutionary steps: Mtn.3 to Mtn1 and Mtn1 to Dp(Mtn1), are accompanied by an overall 5- to 6-fold increase of RNA accumulation. The two changes seem to have occurred in non-African populations since Mtn.3 but not Mtn1 was detected in our sample from tropical Africa, while Mtn1 and Dp (Mtn1) are prevalent in European and North American samples.

Amino Acid Sequence↗

PubMed1990

The pili of Aeromonas hydrophila: identification of an environmentally regulated "mini pilin".

Ultrastructural studies of Aeromonas hydrophila strain AH26 revealed two distinctive pilus types: "straight" pili appear as brittle, rod-like filaments, whereas "flexible" pili are supple and curvilinear. Straight pili are produced constitutively under all tested conditions of growth. In contrast, the expression of flexible pili is regulated by physical and chemical variables, being produced at 22 vs. 37 degrees C, in a liquid vs. a solid medium, and when the availability of free-iron is reduced by the presence of deferoxamine mesylate. Both pilus proteins were purified and biochemically and functionally characterized. The major repeating subunit of the straight pilus is a 17,000-mol wt polypeptide with amino acid sequence homology with Escherichia coli type 1 and Pap pili. The flexible pilus filament is a homopolymer composed of a novel 46 amino acid polypeptide. Resistance of the flexible pilus filament to disaggregation using various chemical treatments was demonstrated; its stability as a polymer and its apparent mechanical strength seem to be conferred by a 20 amino acid hydrophobic, COOH-terminal domain. Purified straight pili lack hemagglutinating function. In contrast, purified flexible pili cause the agglutinin of human, guinea pig, ovine, bovine, and avian erythrocytes, although this property could only be demonstrated in the presence of divalent cations and was most evident at 4 vs. 22 degrees C. Taken together, these results suggest that the pathogenic and ecological roles of the flexible pilus are related to this species' existence as a free-living organism in aquatic environments and its ability to cause infections, both in cold-blooded vertebrates and the human intestine.

Aeromonas↗

PubMedDate not supplied

Cystic lymphangioma of the transverse colon: report of a case and review of the literature.

A 32-year-old Chinese man with cystic lymphangioma of the transverse colon is described. He presented with a 1-year history of altered bowel habits. Double-contrast barium enema study demonstrated a submucosal lesion in the midportion of the transverse colon with intact mucosa. Computed tomography (CT) showed a round 3.0-cm submucosal cystic mass lesion. Colonoscopy revealed a smooth, soft polypoid mass on a broad base. He underwent segmental resection of the colon. Histologically, the lesion was characterized by cystic lymphangioma originating from the submucosa. The clinical features, radiology, appropriate treatment, and possible pathogenesis of colonic lymphangioma are discussed.

Adult↗