Campylobacter infections have been increasingly recognized as major causes of human illness. Campylobacter fetus has been identified as a cause of bacteremia, and disseminated infections particularly in immunocompromised hosts, such as patients with malignancies and AIDS, or neonates. In ungulates, the natural hosts to this organism, C. fetus causes chronic mucosal infection, especially of the genito-urinary tract, and may be transmitted venereally. We have identified a family of surface array proteins (SAP) that encapsulate most, if not all, wild type C. fetus cells. Presence of these regular, paracrystalline SAPs renders C. fetus serum- and phagocytosis-resistant and bacteremic mice, whereas SAP(-) spontaneous mutants have these properties. Further, C. fetus can change the size of its predominant SAP. Such changes are associated with changes in antigenicity and crystalline structure. Two serotypes (A and B) of C., fetus have been recognized, based on lipopolysaccharide (LPS) characteristics. SAP from type A and B cells differ in N-terminus, pI, and specificity of binding to LPS. Attachment of SAP to the cell-surface is dependent on divalent cations. These studies of C. fetus have uncovered a variety of phenotypic characteristics. Of particular interest is the phenomenon of antigenic variation.
The aims of this study are to understand the structural basis of the various properties identified (LPS- binding, cation-binding, complement interaction, antigenic sites, protein export functions) and to understand the basis for variation in SAP production. We will use genetic approaches to these problems. First, we plan to create isogeneic strains with defined mutations in the sapA locus. We will use miniTn3 mutagenesis of the cloned sapA gene in E. coli with transfer back into C. fetus to create a family of defined mutants, and then assay these strains for their phenotypic properties. Alternative approaches consist of creating chimeras of the A and B proteins, cloning the putative sapB gene from a type B strain, creating peptides using PCR, to inhibit specific functions, and by site-directed mutagenesis of identified points. To study regulation, we plan to clone sapA homologs that are silent to map their promoter regions and regions for potential recombination. Mutants of upstream regulatory loci will be made and assayed for expression of SAP phenotype. Finally, we plan to clone the recA gene, and then create an isogeneic recA(-) mutant to study the role of homologous recombination in antigenic variability.
|Keo, Thormika; Collins, Jennifer; Kunwar, Pratima et al. (2011) Campylobacter capsule and lipooligosaccharide confer resistance to serum and cationic antimicrobials. Virulence 2:30-40|
|Tu, Zheng-Chao; Gaudreau, Christiane; Blaser, Martin J (2005) Mechanisms underlying Campylobacter fetus pathogenesis in humans: surface-layer protein variation in relapsing infections. J Infect Dis 191:2082-9|
|Tu, Zheng-Chao; Eisner, William; Kreiswirth, Barry N et al. (2005) Genetic divergence of Campylobacter fetus strains of mammal and reptile origins. J Clin Microbiol 43:3334-40|
|Tu, Zheng-Chao; Hui, John; Blaser, Martin J (2004) Conservation and diversity of sap homologues and their organization among Campylobacter fetus isolates. Infect Immun 72:1715-24|
|Tu, Zheng-Chao; Zeitlin, Gary; Gagner, Jean-Pierre et al. (2004) Campylobacter fetus of reptile origin as a human pathogen. J Clin Microbiol 42:4405-7|
|Grogono-Thomas, R; Blaser, M J; Ahmadi, M et al. (2003) Role of S-layer protein antigenic diversity in the immune responses of sheep experimentally challenged with Campylobacter fetus subsp. fetus. Infect Immun 71:147-54|
|Tu, Zheng-Chao; Wassenaar, Trudy M; Thompson, Stuart A et al. (2003) Structure and genotypic plasticity of the Campylobacter fetus sap locus. Mol Microbiol 48:685-98|
|Leonard 2nd, Edward E; Takata, Tohru; Blaser, Martin J et al. (2003) Use of an open-reading frame-specific Campylobacter jejuni DNA microarray as a new genotyping tool for studying epidemiologically related isolates. J Infect Dis 187:691-4|
|Tu, Z C; Ray, K C; Thompson, S A et al. (2001) Campylobacter fetus uses multiple loci for DNA inversion within the 5' conserved regions of sap homologs. J Bacteriol 183:6654-61|
|Ray, K C; Tu, Z C; Grogono-Thomas, R et al. (2000) Campylobacter fetus sap inversion occurs in the absence of RecA function. Infect Immun 68:5663-7|
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