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K Barr

Publications and source records attributed to K Barr.

33 records · Page 2Linked to original sources
PubMed1987

Biosynthesis of enterobacterial common antigen in Escherichia coli. In vitro synthesis of lipid-linked intermediates.

An in vitro system was developed to study the biosynthesis of enterobacterial common antigen (ECA). Membranes of Escherichia coli were found to possess an enzyme activity that catalyzes the transfer of UDP-N-acetyl-acetylglucosamine-1-phosphate from UDP-N-acetyl-glucosamine (UDP-GlcNAc) to an endogenous lipid acceptor according to the reaction UDP-GlcNAc + P-lipid----GlcNAc-PP-lipid + UMP. The lipid-linked product was tentatively identified as GlcNAc-pyrophosphorylundecaprenol (lipid I) based on a comparison of its chemical and chromatographic properties with those of authentic GlcNAc-pyrophosphorylundecaprenol. The enzyme was dependent on the presence of Mg2+ for activity, and the reaction catalyzed by the enzyme was totally inhibited by the antibiotic tunicamycin in both the forward and reverse directions. Incubation of membranes with both UDP-N-acetylmannosaminuronic acid (UDP-ManNAcA) and UDP-GlcNAc resulted in the conversion of lipid I to a more polar compound, lipid II. The synthesis of lipid II was dependent on prior synthesis of lipid I. Characterization of the saccharide moiety of lipid II resulted in the identification of this compound as ManNAcA-GlcNAc-pyrophosphorylundecaprenol.

Antigens, Bacterial↗
PubMed1986

Beta-lactam antibiotics increase the frequency of plasmid transfer in Staphylococcus aureus.

The transfer of a plasmid specifying tetracycline resistance between different derivatives of Staphylococcus aureus by phage mediated conjugation was enhanced 100- to 1000-fold by exposure of the culture to subinhibitory concentrations of beta-lactam agents. A variety of other antibiotics, including vancomycin and teicoplanin, had no such effect. The enhanced frequency of transfer was probably due to the formation of large bacterial aggregates.

Anti-Bacterial Agents↗
PubMed1986

Resistance in Escherichia coli after single dose ampicillin to treat gonorrhoea.

Patients with uncomplicated gonorrhoea were treated with a single dose of either ampicillin 3 g orally or procaine penicillin 2.4 MIU by injection, both with probenecid 1 g orally. The proportion of faecal Escherichia coli resistant to ampicillin before and a week after treatment was assessed. Of 55 patients treated with ampicillin who initially possessed sensitive flora, 25 (45.5%) became colonised subsequently by resistant E coli. Resistance to ampicillin, together with resistance to some other antimicrobials, was transferable in vitro. Penicillin, however, selected resistant E coli in only four (14.3%) out of 28 patients with initially sensitive flora. There was no difference in therapeutic response between the two agents. Intramuscular penicillin appeared to offer appreciably greater microbiological benefits than oral ampicillin in treating gonorrhoea.

Ampicillin↗
PubMed1985

Suppression in Xenopus laevis: thymus inducer, spleen effector cells.

Studies were carried out on suppressor function in the amphibian Xenopus laevis, the South African clawed toad. Suppression by the thymus of haemagglutinin (HA) production by spleen is antigen-dependent, partially specific and not MHC-restricted in this species (Ruben, Buenafe & Seivert, 1983). Three questions were considered in this study. Does the thymus effect suppression by stimulating peripheralized spleen effector cells, or do effector cells reside within the thymus? Do macrophages participate in the induction and/or expression of thymus-dependent suppressor function? Can thymus suppressor and helper functions be distinguished by using irradiation treatment? The capacity of immunized thymus to suppress HA when co-cultured with spleen fragments from immunized, cyclophosphamide (CyP)-injected animals was tested. Immunized thymus failed to suppress the high levels of HA production by spleen fragments from CyP-treated, immunized donors. Colloidal carbon injection resulted in blockade of macrophage function, and both the capacity of thymuses to suppress and of spleens to be suppressed in co-cultures. Finally, the effect of thymus exposure to gamma-irradiation in vitro was tested using autogeneic thymus/spleen combinations. This enabled the visualization of thymic helper function, which is MHC-restricted in Xenopus (Bernard et al., 1981). Four dosages of irradiation were tested after antigen challenge. The highest HA titres were produced by spleen co-cultures with thymuses which had received 1000 rads. We conclude that suppression of HA production in spleen is not the result of thymus suppressor effector cells, but that suppressor function is mediated by thymus inducer cells which stimulate suppressor effectors in spleen. Both the thymic inducers and effectors in the spleen are sensitive to CyP and macrophage blockade. Our studies further suggest that we are able to distinguish between the thymic functions of help and suppression in Xenopus by taking advantage of their differential sensitivities to irradiation. While it has been postulated, on other grounds, that suppression was one of the earliest thymic regulatory functions to have evolved (L.N. Ruben & R.H. Clothier, submitted), here we suggest the presence of sequential activities of more than one cellular subset, as early in evolution as the primitive anuran (tail-less) amphibia.

Animals↗
PubMed1985

Lectin effects on thymic suppression of hemagglutinin production in vitro by spleen fragments from Xenopus laevis, the South African clawed toad.

Suppression of hemagglutinin (HA) production was studied in co-cultures of thymus and spleen fragments from the South African clawed toad, Xenopus laevis. Concanavalin (Con)A and peanut (PNA) and wheatgerm (WGA)agglutinins were tested in conjunction with, or as a substitute for antigenic induction of thymus suppression. While thymuses from animals injected with PNA or WGA and antigen expressed suppressor function, those treated with Con A and antigen did not. Spleen fragments from animals challenged with PNA or WGA and antigen were resistant to suppression by normal thymus in reciprocal co-cultures; those receiving Con A and antigen alone were equally suppressible. All three lectins can substitute for antigen in the induction of thymus suppression. However, only PNA and WGA induce suppressor function in Xenopus spleen. Since WGA can induce splenic suppression in adult thymectomized animals, it is now possible to distinguish thymic and peripheral aspects of suppression of HA in this primitive vertebrate.

Animals↗
PubMed1984

Occurrence of novel antigenic phosphoinositol-containing sphingolipids in the pathogenic yeast Histoplasma capsulatum.

Five alkali-stable lipids from the yeast phase of Histoplasma capsulatum have been purified and analyzed. Each compound has equimolar amounts of hydroxysphinganine (phytosphingosine) and a hydroxy or nonhydroxy 24:0 fatty acid. All yield inositol phosphate after acid hydrolysis, and several are novel in that they also yield dimannosylinositol (compound V) and isomeric galactosyldimannosylinositols (compounds VI and VIII) after strong ammonolysis. The foregoing as well as other data suggest that compound V is a dimannosylinositolphosphoceramide and compounds VI and VIII are galactosyldimannosylinositolphosphoceramides with isomeric head groups. The chromatographic behavior of compounds II and III indicates that they are similar to the inositolphosphoceramides previously observed in Saccharomyces cerevisiae. Compounds V and VI are virtually absent from the mycelial phase of H. capsulatum. Antibodies that react with compounds V, VI, and VIII have been detected in sera from patients with histoplasmosis.

Antibody Specificity↗
PubMed1984

Carbohydrate structures of three novel phosphoinositol-containing sphingolipids from the yeast Histoplasma capsulatum.

From the yeast phase of the human pathogen Histoplasma capsulatum, three novel glycolipids were isolated, shown to react with sera from histoplasmosis patients, and partially characterized: compound V, ceramide-P-inositol-[mannose2]; compound VI, ceramide-P-inositol-[mannose2, galactose]; compound VIII, an isomer of compound VI [Barr, K., & Lester, R.L. (1984) Biochemistry (preceding paper in this issue)]. Ammonolysis of these lipids has yielded all the carbohydrate (oligosaccharides V, VI, and VIII) as novel, intact oligosaccharides suitable for characterization. Anomeric configurations were determined by specific glycosidase digestion and by the stability of peracetylated saccharides to CrO3 oxidation. Linkages were established by methylation analysis. These experiments yielded the following structural assignments: (formula; see text) The occurrence of galactofuranose is novel for glycosphingolipids, and it is noteworthy that compound VI is immunoreactive.

Carbohydrate Conformation↗
PubMed1983

Characterization of lactose transport in Kluyveromyces lactis.

We have determined that lactose uptake in Kluyveromyces lactis is mediated by an inducible transport system. Induction, elicited by lactose or galactose, of the transporter required protein synthesis. Transport of lactose required an energy-generating system and occurred by an active process, since an intracellular lactose concentration 175 times greater than the extracellular concentration could be obtained. The Km for lactose transport was about 2.8 mM in uninduced and lactose- or galactose-induced cells. The lactose transporters in K. lactis and Escherichia coli appear to be different since they respond uniquely to inhibition by substrate analogs.

2,4-Dinitrophenol↗
PubMedDate not supplied

The congo red stain revisited.

The Congo red stain has undergone several modifications since it was first used by Bennhold in 1922 in order to increase the specificity for staining amyloid. Most of the laboratories in the United States use the method of Puchtler which uses alkaline Congo red solution. Some of the variables associated with the procedure were investigated by us. Our results showed the following: (1) amyloid showed green birefringence at all levels between 4 to 12 mu thick sections with better visualization of small deposits with increased thickness. Best results were obtained with 8 mu thick sections; (2) omission of the pretreatment with alkaline alcoholic solution of sodium chloride (NaCl) did not affect the sensitivity of the method; (3) the use of polar mounting media had no effect on amyloid and collagen birefringence; (4) 50 percent saturation of the Congo red staining solution with NaCl caused strong staining of collagen, elastic fibers and eosinophilic granules. In addition, collagen showed green birefringence and dichroism and its differentiation from amyloid became difficult; and (5) using the staining solution fully saturated with NaCl, no positive staining was seen with tissues other than amyloid. Collagen and elastic fibers showed red fluorescence which was of less intensity than amyloid. It is our conclusion that the method of Puchtler for detecting amyloid gives better results if the staining solution is fully saturated with NaCl. The pretreatment step may be deleted without compromising the quality of staining. Improved staining of amyloid enhances the specificity of green birefringence, dichroism, and red fluorescence.

Amyloid↗