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Biomedical subjects

A Sutton

Publications and source records attributed to A Sutton.

At least 73 records · Page 4Linked to original sources
PubMed1982

Cloning and expression of the ilvB gene of Escherichia coli K-12.

A plasmid containing the ilvB operon, which codes for acetohydroxy acid synthase I of Escherichia coli K-12, was isolated using a ligated mixture of DNA from plasmid pBR322 and FilvB4 treated with endonuclease SalI. A shortened derivative of this plasmid was isolated by cloning a 3.4 kb bacterial fragment into plasmid pKEN005 to yield plasmid pTCN12. The orientation of the ilvB operon relative to plasmid genes was determined by restriction enzyme mapping. Measurement of the level of the product of the ilvB gene, acetohydroxy acid synthase I, indicated that plasmid pTCN12 contained a functional ilvB promoter and control region. The DNA frm this plasmid was used as a probe to show that the rate of synthesis of ilvB mRNA was proportional to the levels of acetohydroxy acid synthase I.

Acetolactate Synthase↗
PubMed1982

The mucosal immune response in the neonate.

Human infants are relatively deficient in the IgA system defending mucosal membranes, but are provided via the maternal milk with considerable amounts of SIgA directed against microbes and food antigens to which both mother and infant are exposed. It is possible that serum antibodies may support the mucosal defense as do the lactoferrin, lysozyme and other defense factors present in the milk.

Animals↗
PubMed1982

Differential complement resistance mediates virulence of Haemophilus influenzae type b.

Studies were undertaken to gain insight into the virulence of type b in contrast to the other Haemophilus influenzae capsular types. A relationship was found between the comparative virulence of H. influenzae types in humans and their resistance to the bactericidal effect of antibody-free complement. Type b was most resistant to the bactericidal effect of complement. The other types could be divided into three groups based upon their susceptibility to complement; this grouping was also related to their structural similarities. No association between virulence and either the biotype, source of isolate, in vitro association with peripheral polymorphonuclear leukocytes, or the total amount of capsular polysaccharide was found. However, among the type b strains, higher levels of cell-associated polysaccharide were associated with increased resistance to complement. The relative virulence of the six H. influenzae types in the infant rat model was generally similar to that in humans. After intraperitoneal challenge, type b and type a strains had the lowest 50% effective doses for bacteremia, removed by several logs from the values of the other types. By intranasal challenge, type b strains produced higher rates and levels of bacteremia than did type a strains. High levels of natural bactericidal antibodies to types c and e were found in adult female rats; this finding alone could not account for the differences in virulence among the H. influenzae types in the infant rat model. We propose that the virulence of type b strains is due to their greater resistance to the bactericidal activity of serum complement alone. Resistance to type b disease requires serum antibody to induce the complement-mediated reaction.

Animals↗
PubMed1982

Mutations in genes cpxA and cpxB of Escherichia coli K-12 cause a defect in acetohydroxyacid synthase I function in vivo.

Mutations in Escherichia coli genes cpxA and cpxB together cause a temperature-sensitive defect in isoleucine and valine syntheses that is related specifically to acetohydroxyacid synthase I. This enzyme catalyzes the first pair of homologous reactions required for the synthesis of these two amino acids. At both permissive and nonpermissive temperatures, mutant cells containing ilvB (the structural gene for acetohydroxyacid synthase I) cloned in a derivative of plasmid pBR322 synthesized comparable amounts of ilvB mRNA and contained several times the enzyme activity normally required to sustain exponential growth, yet these cells remained temperature sensitive for growth in the absence of isoleucine and valine. These observations suggest that the primary effect of the cpx mutations is to block enzyme function in vivo. The enzyme was unstable in mutant cells at growth temperatures above 37 degrees C, but this instability appeared to be a secondary effect on the cpx mutations.

Acetolactate Synthase↗
PubMed1982

The requirement of specific anticapsular IgG for killing of Haemophilus influenzae by the alternative pathway of complement activation.

Employing an in vitro bactericidal assay using C4-deficient guinea pig serum (C4D-GPS), we evaluated the ability of the alternative pathway to kill a number of strains of encapsulated and unencapsulated Haemophilus influenzae (HI). Complement activation occurred, but no bactericidal activity was observed against any of the tested HI in nonimmune C4D-GPS without detectable antibody to HI-type b (HIb) capsular polysaccharide (HIb-ps). In the presence of high-titered human anti- (type b) IgG, C4D-GPS killed the encapsulated strains. Restoration of classical pathway activity by the addition of purified C4 to C4D-GPS, which contained antibody to somatic antigens, resulted in killing of some strains of both encapsulated and unencapsulated HI. In nonimmune C4D-GPS the alternative pathway is activated but does not mediate bactericidal activity. The addition of specific high-titered anticapsular IgG results in killing of encapsulated HI by the alternative pathway in guinea pig serum.

Animals↗
PubMed1980

Preparation, characterization, and immunogenicity of Haemophilus influenzae type b polysaccharide-protein conjugates.

A method is presented for covalently bonding Haemophilus influenzae type b capsular polysaccharide (HIB Ps) to several proteins. The method is efficient and relies upon the use of adipic dihydrazide as a spacer between the capsular polysaccharide and the carrier protein. In contrast to the poor immunogenicity of the purified HIB Ps in mice and rabbits, the HIB Ps-protein conjugates induced serum anti-type b antibodies having bactericidal activity at levels shown to be protective in humans when low doses were injected subcutaneously in a saline solution. The antibody response in mice was related to the dose of the conjugates, increased with the number of injections, and could be primed by the previous injection of the carrier protein. The HIB Ps-protein conjugates were immunogenic in three different mouse strains. The importance of the carrier molecule for the enhanced immunogenicity of the HIB Ps-protein conjugates was shown by the failure of HIB Ps hybrids prepared with either the homologous polysaccharide or pneumococcus type 3 polysaccharide to induce antibodie in mice. Rabbits injected with the HIB Ps-protein conjugates emulsified in Freund's adjuvant produced high levels of serum anti-type b antibodies which induced a bactericidal effect upon H. influenzae type b organisms. It is proposed that the HIB Ps component of the polysaccharide protein conjugates has been converted to a thymic-dependent immunogen. This method may be used to prepare protein-polysaccharide conjugates with HIB Ps and other polysaccharides to be considered for human use.

Animals↗
PubMed1980

Regulation of cyclic AMP of the ilvB-encoded biosynthetic acetohydroxy acid synthase in Escherichia coli K-12.

The biosynthetic acetohydroxy acid synthase activities of E. coli K 12 are encoded by three genetic loci namely, ilvB (acetohydroxy acid synthase I), ilvG (acetohydroxy acid synthase II) and ilvHI (acetohydroxy acid synthase III). The previously reported involvement of cyclic AMP in the regulation of the biosynthetic acetohydroxy acid synthase isozymes in E. coli K-12 was found to be due to the effect of this nucleotide on the expression of ilvB. Cyclic AMP had no effect on acetohydroxy acid synthase activity in strains lacking wild-type ilvB activity but containing the remaining isozymes. Very little activity of acetohydroxy acid synthase coded for by ilvV was found when ppGpp and cyclic AMP were severely limited. Addition of cyclic AMP under these conditions increased ilvB expression 24-fold. The data suggest that in addition to multivalent repression and ppGpp, cyclic AMP plays a major role in the regulation of the ilvB biosynthetic operon.

Acetolactate Synthase↗
PubMed1980

Comparative analysis of plasmids and some metabolic characteristics of Escherichia coli K1 from diseased and healthy individuals.

All 62 Escherichia coli strains possessing the K1 capsular polysaccharide contained plasmid deoxyribonucleic acid, and most (51 of 62) had multiple plasmid species. The incidence of hemolysins, colicins, hemagglutinins for human erythrocytes, and plasmids did not differ among K1 strains isolated from the cerebrospinal fluids of neonates with meningitis or among those strains isolated from the stools of healthy individuals of all ages. There was an association between E. coli serotype and the distribution of plasmids, hemolysins, and colicins among the K1 strains. A common plasmid of about 65 megadaltons was found in all of the O18 serotypes; the similarity of these plasmids was confirmed by analysis with the restriction endonuclease EcoRI. Plasmids of similar molecular weight were also present in E. coli strains of the O7:K1 and O75:K100 serogroups. These data are consistent with the hypothesis that E. coli strains of the same serotype may be descendents of a single bacterial clone.

Adult↗
PubMed1979

Form variation in Escherichia coli K1: determined by O-acetylation of the capsular polysaccharide.

The chemical basis for the alternating antigenic change called form variation noted for the Escherichia coli K1-capsular polysaccharide has been shown by 13C nuclear magnetic resonance to be a result of random O-acetylation of C7 and C9 carbons of the alpha-2-8-linked sialic acid homopolymer. A serologic method (antiserum agar) was developed to identify and isolate the form variants. The O-acetyl positive and O-acetyl negative K1 polysaccharides had unique biochemical and immunologic properties. The O-acetyl-positive variants resisted neuraminidase hydrolysis in contrast to the susceptibility of the O-acetyl negative variant to this enzyme. In addition, O-acetylation altered the antigenicity of the O-acetyl polysaccharides. When injected as whole organisms, O-acetyl positive organisms produced anti-K1 -antibodies in rabbits specific for this polysaccharide variant. O-acetyl negative organisms were comparatively less immunogenic; however, antibodies induced by these organisms reacted with both K1 polysaccharide variants. Burros, injected with either variant, produced antibodies reactive with both K1 polysaccharides.

Acetylation↗
PubMed1979

Comparative immunogenicity of vaccines prepared from capsular polysaccharides of group C Neisseria meningitidis O-acetyl-positive and O-acetyl-negative variants and Escherichia coli K92 in adult volunteers.

Three structurally and antigenically similar capsular polysaccharides, two derived from group C Neisseria meningitidis (O-acetyl-positive and O-acetyl-negative variants) and one from Escherichia coli K92, which cross-reacts with polysaccharide from group C N. meningitidis, were compared for their ability to induce anticapsular and bactericidal antibodies to group C N. meningitidis in adult volunteers. All three vaccines elicited group C-specific serum antibodies. The vaccine derived from the O-acetyl-negative variant was the most immunogenic of the three vaccines. With use of radiolabeled O-acetyl-positive group C N. meningitidis polysaccharide antigen, the geometric mean titers of antibody in serum were 41.7 microgram/ml to the O-acetyl-negative variant, 22.8 microgram/ml to the O-acetyl-positive variant, and 7.1 microgram/ml to E. coli K92. Antibodies induced by all three vaccines were bactericidal for both of the group C N. meningitidis polysaccharide variants. An inverse relation between the comparative immunogenicity of the O-acetyl-negative polysaccharide and the virulence of group C N. meningitidis was found.

Adult↗