VTechWorks staff will be away for the winter holidays starting Tuesday, December 24, 2024, through Wednesday, January 1, 2025, and will not be replying to requests during this time. Thank you for your patience, and happy holidays!
 

Investigation of Haemophilus somnus Virulence Factors: Lipooligosaccharide Sialylation and Inhibition of Superoxide Anion Production

Simple item page
dc.contributor.authorHoward, Michael D.en
dc.contributor.committeechairInzana, Thomas J.en
dc.contributor.committeememberGregory, Eugene M.en
dc.contributor.committeememberBuechner-Maxwell, Virginia A.en
dc.contributor.committeememberSchurig, Gerhardt G.en
dc.contributor.committeememberToth, Thomas E.en
dc.contributor.departmentVeterinary Medical Sciencesen
dc.date.accessioned2014-03-14T20:09:35Zen
dc.date.adate2005-04-20en
dc.date.available2014-03-14T20:09:35Zen
dc.date.issued2005-04-05en
dc.date.rdate2005-04-20en
dc.date.sdate2005-04-14en
dc.description.abstractVirulent strains of the bovine opportunistic pathogen Haemophilus somnus (Histophilus somni) cause multi-systemic diseases in cattle. One of the reported virulence factors that H. somnus may use to persist in the host is resistance to intracellular killing. It is reported in this dissertation that H. somnus significantly (P <0.001) inhibited production of superoxide anion (O2-) by bovine mammary and alveolar macrophages as well as by polymorphonuclear leukocytes. Inhibition of O2- production was time- and dose-dependent and did not occur after incubation with Escherichia coli, H. influenzae, or Brucella abortus. Non-viable H. somnus, purified lipooligosaccharide (LOS), or cell-free supernatant from mid-log phase cultures did not inhibit O2- production, indicating that O2- inhibition required contact with live H. somnus. Commensal isolates of H. somnus were less capable or incapable of inhibiting macrophage O2- production compared to isolates tested from disease sites. H. somnus shares conserved epitopes in its LOS with Neisseria gonorrhoeae, N. meningitidis, and H. influenzae, and can also undergo structural phase variation of these LOS epitopes. Sialylation of the terminal galactose of H. somnus LOS is another reported virulence mechanism. Current sequencing of the genomes of H. somnus strains 2336 (pathogenic) and 129Pt (commensal) has enabled in silico identification of three open reading frames (ORFs) involved in sialylation. The ORFs-1 (hsst-I) and -2 (hsst-II) had BLASTx homology to sialyltransferases, while ORF-3 (neuAhs) had BLASTx homology to CMP-sialic acid synthetases. These ORFs were amplified by PCR and cloned into the expression vector pCWOri+. Thin layer chromatography of the hsst-I gene product showed this sialyltransferase exhibited preference for sialylation of terminal N-acetyllactosamine (LacNAc, beta-Gal-[1,4]-beta-GlcNAc-R). However, Hsst-II preferentially sialylated lacto-N-biose (LNB, beta-Gal-[1,3]-beta-GlcNAc-R). In this study, phase variation of the terminal linkage in isolate 738 from a 3 linked galactose (LNB) to a 4 linked galactose (LacNac) was demonstrated. Such variation of a glycose linkage appears to be a novel mechanism of LOS phase variation. Furthermore, the ability of sialylated strain 738 LOS vs de-sialylated strain 738 LOS to induce Toll-like receptor 4 signaling was decreased by 28%, as determined by ELISA for Macrophage Inflammatory Protein-2. Therefore, sialylated LOS may aid H. somnus to avoid host innate immunity.en
dc.description.degreePh. D.en
dc.identifier.otheretd-04142005-223651en
dc.identifier.sourceurlhttp://scholar.lib.vt.edu/theses/available/etd-04142005-223651/en
dc.identifier.urihttp://hdl.handle.net/10919/26848en
dc.publisherVirginia Techen
dc.relation.haspartETD_MHoward.pdfen
dc.rightsIn Copyrighten
dc.rights.urihttp://rightsstatements.org/vocab/InC/1.0/en
dc.subjectHistophilus somnien
dc.subjectHaemophilus somnusen
dc.subjectsialic aciden
dc.subjectsialylationen
dc.subjectmicrobial immunityen
dc.subjectvirulence factorsen
dc.subjectsuperoxide anionen
dc.titleInvestigation of Haemophilus somnus Virulence Factors: Lipooligosaccharide Sialylation and Inhibition of Superoxide Anion Productionen
dc.typeDissertationen
thesis.degree.disciplineVeterinary Medical Sciencesen
thesis.degree.grantorVirginia Polytechnic Institute and State Universityen
thesis.degree.leveldoctoralen
thesis.degree.namePh. D.en

Files

Original bundle
Now showing 1 - 1 of 1
Thumbnail Image
Name:
ETD_MHoward.pdf
Size:
3.13 MB
Format:
Adobe Portable Document Format
Download

Collections

Doctoral Dissertations