Konkel, Michael
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Research Interests
Campylobacter jejuni is one of the most commonly reported causes of diarrhea worldwide. The ability of C. jejuni to cause disease is both complex and multi-factorial. Potential virulence determinants include toxins, adherence factors (adhesins), and entry-promoting molecules (invasins). The ability of C. jejuni to bind to cells lining the gastrointestinal tract is proposed to be essential for the development of C. jejuni-mediated enteritis. In addition, the dysentery associated with Campylobacter infection, coupled with the presence of C. jejuni in mucosal cells of infected individuals, has led investigators to hypothesize that C. jejuni enteritis is directly related to the organism’s ability to invade the cells lining the gastrointestinal tract. Entering host cells enables bacteria to evade innate host immune responses including complement activity and phagocytosis by professional phagocytes.

Research in the Konkel laboratory focuses on the characterization of C. jejuni-host cell interactions with the aim of identifying and characterizing binding and entry-promoting proteins. We have cloned and partially characterized a 37 kDa protein from C. jejuni, termed CadF, that mediates the binding of C. jejuni to fibronectin (Fn). CadF is conserved among all C. jejuni and C. coli isolates tested to date. Other work in the lab has revealed that C. jejuni synthesize and secrete proteins upon cultivation with mammalian cells. These secreted bacterial proteins are called the Campylobacter invasion antigens (Cia). A mutation in the gene encoding a 73 kDa secreted protein (CiaB) results in a non-invasive phenotype. Several different approaches (i.e., comparative and functional genomics, microarrays, and proteomics) are currently being used to identify and characterize additional C. jejuni virulence genes and their products.

Fig. 1. Model of C. jejuni binding and entry into host cells. Intimate binding of C. jejuni is mediated by multiple adhesins, including CadF and PEB1, and is a requirement for internalization. CadF binds Fn, which in turn binds to host cell a 5 b 1 integrin receptors. The binding of C. jejuni to cell-associated Fn promotes and stabilizes integrin clustering, which in turn stimulates the co-clustering of focal adhesion cytoskeletal elements and cellular signaling molecules. Additional assays revealed that the binding of C. jejuni to cell-associated Fn leads to the phosphorylation of paxillin. A subset of the newly synthesized Cia proteins are secreted and translocated into the cytoplasm of target cells upon the irreversible binding of C. jejuni to the intestinal epithelial cells. These translocated bacterial proteins presumably stimulate host cell signaling events, promoting C. jejuni uptake. The binding of C. jejuni to host cells is, in itself, able to induce IL-8 secretion.

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Job Opening - Postdoctoral Research Position

Publications

Malik-Kale, P., Raphael, B.H., Parker, C.A., Joens, L., Klena, J.D, Quiñones, B., Keech, A.M., and M.E. Konkel. Characterization of genetically-matched isolates of Campylobacter jejuni reveals mutations in genes involved in flagellar biosynthesis alter the organism’s virulence potential. Appl. Environ. Microbiol.  (In press). Link

Konkel, M.E., Christensen, J.E., Dhillon, A.S., Lane, A.B., Hare-Sanford, R., D. Schaberg, D., and C. Larson.  Campylobacter jejuni strains compete for colonization of broiler chicks. Appl. Environ. Microbiol.  (In press). Link

Besser, T.E., Shaikh, N., Holt, N.J. Tarr, P.I., Konkel, M.E., Whittam, T., and J. Bono.  Shiga toxin-encoding bacteriophage insertion sites identify Escherichia coli O157:H7 genotypes biased in distribution to the bovine reservoir. Appl. Environ. Microbiol. 73:671-679, 2007. Link

Mamelli, L., Dedieu, L., Dé, E., Konkel, M.E., Pagès, J.-M. and J.-M. Bolla. Chromosomal His-Tagging:  An alternative approach to membrane protein purification. Proteomics. 7:399-402, 2007. Link

Mamelli, L., Pagès, J.-M., Konkel, M.E., and J.-M. Bolla. Expression and purification of native and truncated forms of CadF, an outer membrane protein of Campylobacter. Int. J. Biol. Macromol. 39:135-40, 2006. Link

Konkel, M.E., Christensen, J.E., Keech, A.M., Monteville, M.R., Klena, J.D., and S.G. Garvis. Identification of a fibronectin-binding domain within the Campylobacter jejuni CadF protein. Mol. Microbiol.57:1022-1035, 2005. Link

Raphael, B.H., Pereira , S., Flom, G.A., Zhang, Q., Ketley, J.M., and M.E. Konkel . The Campylobacter jejuni response regulator, CbrR, modulates sodium deoxycholate resistance and chicken colonization. J. Bacteriol. 187:3662-3670, 2005. Link

Palazzolo, A.M,, Suquet, C., Konkel, M.E., and J.K. Hurst. Green fluorescent protein-expressing Escherichia coli as a selective probe for HOCl generation within neutrophils. Biochem. 44:6910-6919, 2005. Link

Klena, J.D., Parker, C.T., Knibb, K., J. Ibbitt, J.C., Devane, P.M.L., Horn, S.T., Miller, W.G., and M.E. Konkel . Differentiation of Campylobacter coli, Campylobacter jejuni, Campylobacter lari and Campylobacter upsaliensis using a multiplex PCR developed from the nucleotide sequence of the lipid A gene lpxA.J. Clin. Microbiol. 42:5549-5557, 2004. Link

Konkel , M.E. , Klena, J.D., Rivera-Amill, R., Monteville, M.R., Biswas, D., Raphael, B., and J. Mickelson. Secretion of virulence proteins from Campylobacter jejuni is dependent on a functional flagellar export apparatus. J. Bacteriol. 186:3296-303, 2004. Link

Siegesmund, A.M., Konkel, M.E., Klena, J.D., and P.F. Mixter. Campylobacter jejuni infection of differentiated THP-1 macrophages results in interleukin 1-beta release and caspase 1-independent apoptosis. Microbiol. 150:561-569, 2004. Link

Mixter, P.F., Klena, J.D., Flom, G.A., Siegesmund, A.M., and M.E. Konkel. In vivo tracking of Campylobacter jejuni using a novel recombinant expressing green fluorescent protein. Appl. Environ. Microbiol. 69: 2864-2874, 2003. Link

Monteville, M.R., Yoon, J.E., and M.E. Konkel. Maximal adherence and invasion of INT 407 cells by Campylobacter jejuni requires the CadF outer membrane protein and microfilament reorganization. Microbiol. 149:153-65, 2003. Link

Monteville, M.R., and M.E. Konkel. Fibronectin-facilitated invasion of T84 eukaryotic cells by Campylobacter jejuni occurs preferentially at the basolateral cell surface. Infect. Immun. 70:6665-71, 2002. Link

Konkel , M.E., Monteville, M.R., Rivera-Amill, V., L.A. Joens. The pathogenesis of Campylobacter jejuni-mediated enteritis. Curr. Issues Intest. Microbiol. 2:55-71, 2001. Link

Ziprin, R.L., Young, C.R., Byrd, J.A., Stanker, L.H., Hume, M.E., and Gray, S.A., Kim, B.J., and M.E. Konkel. Role of Campylobacter jejuni potential virulence proteins in cecal colonization. Avian Dis. 45:549-5, 2001. Link

Rivera-Amill, V., Kim, B.J., Seshu, J., and M.E. Konkel. Secretion of the virulence associated Campylobacter invasion antigens from Campylobacter jejuni requires a stimulatory signal. J. Infect. Dis. 183:1607-16, 2001. Link

Konkel , M.E. , and P.F. Mixter. Flow cytometric detection of host cell apoptosis induced by bacterial infection. Meth. Cell Sci 22:209-15, 2000. Link

Pritchett, L.C., Konkel, M.E., Gay, J.M., and T.E. Besser. Identification of DT104 and U302 phage types among Salmonella enterica serotype typhimurium by the polymerase chain reaction. J. Clin. Microbiol. 38:3484-8, 2000. Link

Konkel , M.E. , and K. Tilly. Temperature-regulated expression of bacterial virulence genes Microbes Infect. 2:1-10, 2000. Link