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  • American Society for Microbiology  (34)
  • 1
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    Online Resource
    Incorporation of N -Acetylneuraminic Acid into Haemophilus somnus Lipooligosaccharide (LOS): Enhancement of Resistance to Serum and Reduction of LOS Antibody Binding
    American Society for Microbiology ; 2002
    In:  Infection and Immunity Vol. 70, No. 9 ( 2002-09), p. 4870-4879
    Details
    In: Infection and Immunity, American Society for Microbiology, Vol. 70, No. 9 ( 2002-09), p. 4870-4879
    Abstract: Haemophilus somnus isolates from cases of thrombotic meningoencephalitis, pneumonia, and other disease sites are capable of undergoing a high rate of phase variation in the oligosaccharide component of their lipooligosaccharides (LOS). In contrast, the LOS of commensal strains isolated from the normal reproductive tract phase vary little or not at all. In addition, the LOS of H. somnus shares conserved epitopes with LOS from Neisseria gonorrhoeae , Haemophilus influenzae , and other species that can incorporate sialic acid into their LOS. We now report that growth of disease isolates of H. somnus with CMP- N -acetylneuraminic acid (CMP-NeuAc) or NeuAc added to the medium resulted in incorporation of NeuAc into the LOS. However, NeuAc was not incorporated into the LOS of commensal isolates and one disease isolate following growth in medium containing CMP-NeuAc or NeuAc. Sialylated LOS was detected by an increase in the molecular size or an increase in the amount of the largest-molecular-size LOS electrophoretic bands, which disappeared following treatment with neuraminidase. Sialylated LOS could also be detected by reactivity with Limax flavus agglutinin lectin, which is specific for sialylated species, by dot blot assay; this reactivity was also reversed by neuraminidase treatment. H. somnus strain 2336 LOS was found to contain some sialic acid when grown in medium lacking CMP-NeuAc or NeuAc, although supplementation enhanced NeuAc incorporation. In contrast strain 738, an LOS phase variant of strain 2336, was less extensively sialylated when the growth medium was supplemented with CMP-NeuAc or NeuAc, as determined by electrophoretic profiles and electrospray mass spectrometry. The sialyltransferase of H. somnus strain 738 was confirmed to preferentially sialylate the Galβ-(1-3)-GlcNAc component of the lacto- N -tetraose structure by capillary electrophoresis assay. Enhanced sialylation of the strain 2336 LOS inhibited the binding of monoclonal antibodies to LOS by enzyme immunoassay and Western blotting. Furthermore, sialylation of the LOS enhanced the resistance of H. somnus to the bactericidal action of antiserum to LOS. Sialylation and increased resistance to killing by normal serum also occurred in a deletion mutant that was deficient in the terminal Gal-GlcNAc disaccharide. LOS sialylation may therefore be an important virulence mechanism to protect H. somnus against the host immune system.
    Type of Medium: Online Resource
    ISSN: 0019-9567 , 1098-5522
    URL: Article
    DOI: 10.1128/IAI.70.9.4870-4879.2002
    RVK:
    XA 10000
    Language: English
    Publisher: American Society for Microbiology
    Publication Date: 2002
    detail.hit.zdb_id: 1483247-1
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  • 2
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    Antigenic Diversity of Haemophilus somnus Lipooligosaccharide: Phase-Variable Accessibility of the Phosphorylcholine Epitope
    American Society for Microbiology ; 2000
    In:  Journal of Clinical Microbiology Vol. 38, No. 12 ( 2000-12), p. 4412-4419
    Details
    In: Journal of Clinical Microbiology, American Society for Microbiology, Vol. 38, No. 12 ( 2000-12), p. 4412-4419
    Abstract: The lipooligosaccharide (LOS) of Haemophilus somnus undergoes antigenic phase variation, which may facilitate evasion from the bovine host immune response and/or colonization and dissemination. However, LOS antigenic diversity in H. somnus has not been adequately investigated. In this study, monoclonal antibodies (MAbs) specific to various LOS epitopes were used to investigate antigenic variation and stability in LOS from H. somnus strains and phase variants. Clinical isolates of H. somnus exhibited intrastrain, as well as interstrain, antigenic heterogeneity in LOS when probed with MAbs to outer core oligosaccharide epitopes in an enzyme-linked immunosorbent assay (ELISA). However, epitopes reactive with MAbs directed predominately to the inner core heptose region were highly conserved. At least one epitope, which was expressed in few strains, was identified. One LOS component affected by phase variation was identified as phosphorylcholine (PCho), which is linked to the primary glucose residue. Inhibition ELISA, immunoblotting, and electrospray-mass spectrometry were used to confirm that MAb 5F5.9 recognized PCho. LOS reactivity with MAb 5F5.9 was associated with loss of most of the outer core oligosaccharide, indicating that reactivity with PCho was affected by phase variation of the glycose residues in this region. Our results indicate that outer core epitopes of H. somnus LOS exhibit a high degree of random, phase-variable antigenic heterogeneity and that such heterogeneity must be considered in the design of vaccines and diagnostic tests.
    Type of Medium: Online Resource
    ISSN: 0095-1137 , 1098-660X
    URL: Article
    DOI: 10.1128/JCM.38.12.4412-4419.2000
    RVK:
    XA 10000
    Language: English
    Publisher: American Society for Microbiology
    Publication Date: 2000
    detail.hit.zdb_id: 1498353-9
    SSG: 12
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  • 3
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    Online Resource
    Incorporation of N -Acetylneuraminic Acid into Haemophilus somnus Lipooligosaccharide (LOS): Enhancement of Resistance to Serum and Reduction of LOS Antibody Binding
    American Society for Microbiology ; 2002
    In:  Infection and Immunity Vol. 70, No. 11 ( 2002-11), p. 6512-6512
    Details
    In: Infection and Immunity, American Society for Microbiology, Vol. 70, No. 11 ( 2002-11), p. 6512-6512
    Type of Medium: Online Resource
    ISSN: 0019-9567 , 1098-5522
    URL: Article
    DOI: 10.1128/IAI.70.11.6512.2002
    RVK:
    XA 10000
    Language: English
    Publisher: American Society for Microbiology
    Publication Date: 2002
    detail.hit.zdb_id: 1483247-1
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  • 4
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    Race/Ethnicity and Protease Inhibitor Use Influence Plasma Tenofovir Exposure in Adults Living with HIV-1 in AIDS Clinical Trials Group Study A5202
    American Society for Microbiology ; 2019
    In:  Antimicrobial Agents and Chemotherapy Vol. 63, No. 4 ( 2019-04)
    Details
    In: Antimicrobial Agents and Chemotherapy, American Society for Microbiology, Vol. 63, No. 4 ( 2019-04)
    Abstract: AIDS Clinical Trial Group study A5202 (ClinicalTrials.gov identifier NCT00118898) was a phase 3b, randomized, partially blinded equivalence study of open-label atazanavir/ritonavir or efavirenz, plus either placebo-controlled tenofovir disoproxil fumarate/emtricitabine or abacavir/lamivudine, in treatment-naive adults living with HIV-1, evaluating efficacy, safety, and tolerability. We report an analysis of the contribution of participant characteristics to the disposition of tenofovir plasma concentrations. Tenofovir concentration data from a total of 817 individuals (88% of the total number of eligible patients randomly assigned to receive treatment in the TDF-containing arms of A5202) were available for analysis. Pharmacokinetic analysis was performed using nonlinear mixed-effects modeling. One- and two-compartment models with first-order absorption and first-order elimination were evaluated. An exponential error model was used for examination of interindividual variability (IIV), and a proportional and mixed-error model was assessed for residual variability. The final structural model contained two compartments with first-order absorption and elimination. IIV was estimated for apparent clearance (CL/F) and the first-order absorption rate constant ( k a ), and a proportional residual variability model was selected. The final mean parameter estimates were as follows: k a = 2.87 h −1 , CL/F = 37.2 liters/h, apparent volumes of the central and peripheral compartments = 127 and 646 liters, respectively, and apparent intercompartmental clearance = 107 liters/h. In addition to race/ethnicity, creatinine clearance and assignment to atazanavir/ritonavir or efavirenz were significantly associated with CL/F ( P 〈 0.001). In conclusion, race/ethnicity is associated with tenofovir oral CL in HIV-1 positive, treatment-naive adults. This covariate relationship raises questions about the possibility of differences in efficacy and risk of adverse events in different patient populations and suggests that examining preexposure prophylaxis regimens and tenofovir exposure in different race/ethnicity groups be considered.
    Type of Medium: Online Resource
    ISSN: 0066-4804 , 1098-6596
    URL: Article
    DOI: 10.1128/AAC.01638-18
    RVK:
    XA 24552
    Language: English
    Publisher: American Society for Microbiology
    Publication Date: 2019
    detail.hit.zdb_id: 1496156-8
    SSG: 12
    SSG: 15,3
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  • 5
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    Colistin Resistance in Acinetobacter baumannii Is Mediated by Complete Loss of Lipopolysaccharide Production
    American Society for Microbiology ; 2010
    In:  Antimicrobial Agents and Chemotherapy Vol. 54, No. 12 ( 2010-12), p. 4971-4977
    Details
    In: Antimicrobial Agents and Chemotherapy, American Society for Microbiology, Vol. 54, No. 12 ( 2010-12), p. 4971-4977
    Abstract: Infections caused by multidrug-resistant (MDR) Gram-negative bacteria represent a major global health problem. Polymyxin antibiotics such as colistin have resurfaced as effective last-resort antimicrobials for use against MDR Gram-negative pathogens, including Acinetobacter baumannii . Here we show that A. baumannii can rapidly develop resistance to polymyxin antibiotics by complete loss of the initial binding target, the lipid A component of lipopolysaccharide (LPS), which has long been considered to be essential for the viability of Gram-negative bacteria. We characterized 13 independent colistin-resistant derivatives of A. baumannii type strain ATCC 19606 and showed that all contained mutations within one of the first three genes of the lipid A biosynthesis pathway: lpxA , lpxC , and lpxD . All of these mutations resulted in the complete loss of LPS production. Furthermore, we showed that loss of LPS occurs in a colistin-resistant clinical isolate of A. baumannii . This is the first report of a spontaneously occurring, lipopolysaccharide-deficient, Gram-negative bacterium.
    Type of Medium: Online Resource
    ISSN: 0066-4804 , 1098-6596
    URL: Article
    DOI: 10.1128/AAC.00834-10
    RVK:
    XA 24552
    Language: English
    Publisher: American Society for Microbiology
    Publication Date: 2010
    detail.hit.zdb_id: 1496156-8
    SSG: 12
    SSG: 15,3
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  • 6
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    Drug Targeting Mycobacterium tuberculosis Cell Wall Synthesis: Genetics of dTDP-Rhamnose Synthetic Enzymes and Development of a Microtiter Plate-Based Screen for Inhibitors of Conversion of dTDP-Glucose to dTDP-Rhamnose
    American Society for Microbiology ; 2001
    In:  Antimicrobial Agents and Chemotherapy Vol. 45, No. 5 ( 2001-05), p. 1407-1416
    Details
    In: Antimicrobial Agents and Chemotherapy, American Society for Microbiology, Vol. 45, No. 5 ( 2001-05), p. 1407-1416
    Abstract: An l -rhamnosyl residue plays an essential structural role in the cell wall of Mycobacterium tuberculosis . Therefore, the four enzymes (RmlA to RmlD) that form dTDP-rhamnose from dTTP and glucose-1-phosphate are important targets for the development of new tuberculosis therapeutics. M. tuberculosis genes encoding RmlA, RmlC, and RmlD have been identified and expressed in Escherichia coli . It is shown here that genes for only one isotype each of RmlA to RmlD are present in the M. tuberculosis genome. The gene for RmlB is Rv3464. Rv3264c was shown to encode ManB, not a second isotype of RmlA. Using recombinant RmlB, -C, and -D enzymes, a microtiter plate assay was developed to screen for inhibitors of the formation of dTDP-rhamnose. The three enzymes were incubated with dTDP-glucose and NADPH to form dTDP-rhamnose and NADP + with a concomitant decrease in optical density at 340 nm (OD 340 ). Inhibitor candidates were monitored for their ability to lower the rate of OD 340 change. To test the robustness and practicality of the assay, a chemical library of 8,000 compounds was screened. Eleven inhibitors active at 10 μM were identified; four of these showed activities against whole M. tuberculosis cells, with MICs from 128 to 16 μg/ml. A rhodanine structural motif was present in three of the enzyme inhibitors, and two of these showed activity against whole M. tuberculosis cells. The enzyme assay was used to screen 60 Peruvian plant extracts known to inhibit the growth of M. tuberculosis in culture; two extracts were active inhibitors in the enzyme assay at concentrations of less than 2 μg/ml.
    Type of Medium: Online Resource
    ISSN: 0066-4804 , 1098-6596
    URL: Article
    DOI: 10.1128/AAC.45.5.1407-1416.2001
    RVK:
    XA 24552
    Language: English
    Publisher: American Society for Microbiology
    Publication Date: 2001
    detail.hit.zdb_id: 1496156-8
    SSG: 12
    SSG: 15,3
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  • 7
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    Prior Dengue Virus Exposure Shapes T Cell Immunity to Zika Virus in Humans
    American Society for Microbiology ; 2017
    In:  Journal of Virology Vol. 91, No. 24 ( 2017-12-15)
    Details
    In: Journal of Virology, American Society for Microbiology, Vol. 91, No. 24 ( 2017-12-15)
    Abstract: While progress has been made in characterizing humoral immunity to Zika virus (ZIKV) in humans, little is known regarding the corresponding T cell responses to ZIKV. Here, we investigate the kinetics and viral epitopes targeted by T cells responding to ZIKV and address the critical question of whether preexisting dengue virus (DENV) T cell immunity modulates these responses. We find that memory T cell responses elicited by prior infection with DENV or vaccination with tetravalent dengue attenuated vaccines (TDLAV) recognize ZIKV-derived peptides. This cross-reactivity is explained by the sequence similarity of the two viruses, as the ZIKV peptides recognized by DENV-elicited memory T cells are identical or highly conserved in DENV and ZIKV. DENV exposure prior to ZIKV infection also influences the timing and magnitude of the T cell response. ZIKV-reactive T cells in the acute phase of infection are detected earlier and in greater magnitude in DENV-immune patients. Conversely, the frequency of ZIKV-reactive T cells continues to rise in the convalescent phase in DENV-naive donors but declines in DENV-preexposed donors, compatible with more efficient control of ZIKV replication and/or clearance of ZIKV antigen. The quality of responses is also influenced by previous DENV exposure, and ZIKV-specific CD8 T cells from DENV-preexposed donors selectively upregulated granzyme B and PD1, unlike DENV-naive donors. Finally, we discovered that ZIKV structural proteins (E, prM, and C) are major targets of both the CD4 and CD8 T cell responses, whereas DENV T cell epitopes are found primarily in nonstructural proteins. IMPORTANCE The issue of potential ZIKV and DENV cross-reactivity and how preexisting DENV T cell immunity modulates Zika T cell responses is of great relevance, as the two viruses often cocirculate and Zika virus has been spreading in geographical regions where DENV is endemic or hyperendemic. Our data show that memory T cell responses elicited by prior infection with DENV recognize ZIKV-derived peptides and that DENV exposure prior to ZIKV infection influences the timing, magnitude, and quality of the T cell response. Additionally, we show that ZIKV-specific responses target different proteins than DENV-specific responses, pointing toward important implications for vaccine design against this global threat.
    Type of Medium: Online Resource
    ISSN: 0022-538X , 1098-5514
    URL: Article
    DOI: 10.1128/JVI.01469-17
    Language: English
    Publisher: American Society for Microbiology
    Publication Date: 2017
    detail.hit.zdb_id: 1495529-5
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  • 8
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    Pasteurella multocida Expresses Two Lipopolysaccharide Glycoforms Simultaneously, but Only a Single Form Is Required for Virulence: Identification of Two Acceptor-Specific Heptosyl I Transferases
    American Society for Microbiology ; 2007
    In:  Infection and Immunity Vol. 75, No. 8 ( 2007-08), p. 3885-3893
    Details
    In: Infection and Immunity, American Society for Microbiology, Vol. 75, No. 8 ( 2007-08), p. 3885-3893
    Abstract: Lipopolysaccharide (LPS) is a critical virulence determinant in Pasteurella multocida and a major antigen responsible for host protective immunity. In other mucosal pathogens, variation in LPS or lipooligosaccharide structure typically occurs in the outer core oligosaccharide regions due to phase variation. P. multocida elaborates a conserved oligosaccharide extension attached to two different, simultaneously expressed inner core structures, one containing a single phosphorylated 3-deoxy- d -manno-octulosonic acid (Kdo) residue and the other containing two Kdo residues. We demonstrate that two heptosyltransferases, HptA and HptB, add the first heptose molecule to the Kdo 1 residue and that each exclusively recognizes different acceptor molecules. HptA is specific for the glycoform containing a single, phosphorylated Kdo residue (glycoform A), while HptB is specific for the glycoform containing two Kdo residues (glycoform B). In addition, KdkA was identified as a Kdo kinase, required for phosphorylation of the first Kdo molecule. Importantly, virulence data obtained from infected chickens showed that while wild-type P. multocida expresses both LPS glycoforms in vivo, bacterial mutants that produced only glycoform B were fully virulent, demonstrating for the first time that expression of a single LPS form is sufficient for P. multocida survival in vivo. We conclude that the ability of P. multocida to elaborate alternative inner core LPS structures is due to the simultaneous expression of two different heptosyltransferases that add the first heptose residue to the nascent LPS molecule and to the expression of both a bifunctional Kdo transferase and a Kdo kinase, which results in the initial assembly of two inner core structures.
    Type of Medium: Online Resource
    ISSN: 0019-9567 , 1098-5522
    URL: Article
    DOI: 10.1128/IAI.00212-07
    RVK:
    XA 10000
    Language: English
    Publisher: American Society for Microbiology
    Publication Date: 2007
    detail.hit.zdb_id: 1483247-1
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  • 9
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    Pasteurella multocida Heddleston Serovar 3 and 4 Strains Share a Common Lipopolysaccharide Biosynthesis Locus but Display both Inter- and Intrastrain Lipopolysaccharide Heterogeneity
    American Society for Microbiology ; 2013
    In:  Journal of Bacteriology Vol. 195, No. 21 ( 2013-11), p. 4854-4864
    Details
    In: Journal of Bacteriology, American Society for Microbiology, Vol. 195, No. 21 ( 2013-11), p. 4854-4864
    Abstract: Pasteurella multocida is a Gram-negative multispecies pathogen and the causative agent of fowl cholera, a serious disease of poultry which can present in both acute and chronic forms. The major outer membrane component lipopolysaccharide (LPS) is both an important virulence factor and a major immunogen. Our previous studies determined the LPS structures expressed by different P. multocida strains and revealed that a number of strains belonging to different serovars contain the same LPS biosynthesis locus but express different LPS structures due to mutations within glycosyltransferase genes. In this study, we report the full LPS structure of the serovar 4 type strain, P1662, and reveal that it shares the same LPS outer core biosynthesis locus, L3, with the serovar 3 strains P1059 and Pm70. Using directed mutagenesis, the role of each glycosyltransferase gene in LPS outer core assembly was determined. LPS structural analysis of 23 Australian field isolates that contain the L3 locus revealed that at least six different LPS outer core structures can be produced as a result of mutations within the LPS glycosyltransferase genes. Moreover, some field isolates produce multiple but related LPS glycoforms simultaneously, and three LPS outer core structures are remarkably similar to the globo series of vertebrate glycosphingolipids. Our in-depth analysis showing the genetics and full range of P. multocida lipopolysaccharide structures will facilitate the improvement of typing systems and the prediction of the protective efficacy of vaccines.
    Type of Medium: Online Resource
    ISSN: 0021-9193 , 1098-5530
    URL: Article
    DOI: 10.1128/JB.00779-13
    Language: English
    Publisher: American Society for Microbiology
    Publication Date: 2013
    detail.hit.zdb_id: 1481988-0
    SSG: 12
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  • 10
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    Characterization of Two Novel Lipopolysaccharide Phosphoethanolamine Transferases in Pasteurella multocida and Their Role in Resistance to Cathelicidin-2
    American Society for Microbiology ; 2017
    In:  Infection and Immunity Vol. 85, No. 11 ( 2017-11)
    Details
    In: Infection and Immunity, American Society for Microbiology, Vol. 85, No. 11 ( 2017-11)
    Abstract: The lipopolysaccharide (LPS) produced by the Gram-negative bacterial pathogen Pasteurella multocida has phosphoethanolamine (PEtn) residues attached to lipid A, 3-deoxy- d -manno-octulosonic acid (Kdo), heptose, and galactose. In this report, we show that PEtn is transferred to lipid A by the P. multocida EptA homologue, PetL, and is transferred to galactose by a novel PEtn transferase that is unique to P. multocida called PetG. Transcriptomic analyses indicated that petL expression was positively regulated by the global regulator Fis and negatively regulated by an Hfq-dependent small RNA. Importantly, we have identified a novel PEtn transferase called PetK that is responsible for PEtn addition to the single Kdo molecule (Kdo 1 ), directly linked to lipid A in the P. multocida glycoform A LPS. In vitro assays showed that the presence of a functional petL and petK , and therefore the presence of PEtn on lipid A and Kdo 1 , was essential for resistance to the cationic, antimicrobial peptide cathelicidin-2. The importance of PEtn on Kdo 1 and the identification of the transferase responsible for this addition have not previously been shown. Phylogenetic analysis revealed that PetK is the first representative of a new family of predicted PEtn transferases. The PetK family consists of uncharacterized proteins from a range of Gram-negative bacteria that produce LPS glycoforms with only one Kdo molecule, including pathogenic species within the genera Vibrio , Bordetella , and Haemophilus . We predict that many of these bacteria will require the addition of PEtn to Kdo for maximum protection against host antimicrobial peptides.
    Type of Medium: Online Resource
    ISSN: 0019-9567 , 1098-5522
    URL: Article
    DOI: 10.1128/IAI.00557-17
    RVK:
    XA 10000
    Language: English
    Publisher: American Society for Microbiology
    Publication Date: 2017
    detail.hit.zdb_id: 1483247-1
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