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The role of zinc-dependent intercellular adhesion in biofilm formation in Staphylococcus epidermidis

Conrady, Deborah

Abstract Details

2010, PhD, University of Cincinnati, Medicine : Molecular Genetics, Biochemistry, and Microbiology.

Healthcare associated (HA) infections affect 1.5 to 2 million people annually in the United States, with approximately 99,000 fatalities. One third of all HA infections and more than one half of all HA-bloodstream infections are caused by the staphylococcal species S. aureus and coagulase-negative staphylococcus (CoNS), of which S. epidermidis is the most frequent isolate. This normally benign commensal bacterial species infects devices and compromised tissues, as well as immunocompromised hosts. Its pathogenesis in these cases is based on its ability to form biofilms. A biofilm is a specialized bacterial colony that is adherent to abiotic and biotic substrates, in which bacteria are protected from environmental hazards such as antibiotics and host immune defenses.

Biofilm formation in S. epidermidis occurs through three major processes: initial adhesion, accumulation, and maturation. Initial adhesion to a surface is achieved through the exposure of hydrophobic interfaces on dividing cells by autolysin, and by interactions with specific host proteins via MSCRAMMs (microbial surface components recognizing adhesive matrix molecules). After adhesion, bacteria are recruited to the nascent biofilm in the process of accumulation. The protein Aap plays a role during accumulation, but also is responsible for maturation of biofilms of some strains. Other strains secrete the poly-N-acetylglucosamine (PNAG) during the process of maturation. Cloning and expression studies of SdrF (an MSCRAMM), various domain-lengths of Aap, and several Ica proteins (responsible for PNAG synthesis) form the basis for future studies on various aspects of staphylococcal biofilm formation.

The protein Aap is of particular importance to biofilm formation, since it can independently mediate biofilm maturation. Its role in the accumulation phase of polysaccharide-secreting isolates make it very biologically important for both protein and polysaccharide modes of maturation. We have determined that the molecular mechanism of Aap-dependent intercellular adhesion is based on the ability of the tandem repeated G5 domain B-repeat region to self-associate along its length in a zinc-dependent fashion. Chelation of zinc prevents biofilm formation in both S. epidermidis and S. aureus.

The structure of zinc-bound Brpt is of great interest, since it will yield further insight into the mechanism of zinc binding and the nature of the dimerization interface. We have crystallized both native and seleno-methionine-labeled B-repeat point mutants and have attempted molecular replacement and experimental phasing. The diffraction data from these crystals suffer from high anisotropy, leading to a poor signal-to-noise ratio and precluding the determination of initial phases. Future efforts will focus on the improvement of diffraction quality.

Andrew Herr, PhD (Committee Chair)
Thomas Thompson, PhD (Committee Member)
Daniel Hassett, PhD (Committee Member)
Carol Caperelli, PhD (Committee Member)
Alison Weiss, PhD (Committee Member)
Rhett Kovall, PhD (Committee Member)
233 p.

Recommended Citations

Citations

  • Conrady, D. (2010). The role of zinc-dependent intercellular adhesion in biofilm formation in Staphylococcus epidermidis [Doctoral dissertation, University of Cincinnati]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1275920539

    APA Style (7th edition)

  • Conrady, Deborah. The role of zinc-dependent intercellular adhesion in biofilm formation in Staphylococcus epidermidis. 2010. University of Cincinnati, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ucin1275920539.

    MLA Style (8th edition)

  • Conrady, Deborah. "The role of zinc-dependent intercellular adhesion in biofilm formation in Staphylococcus epidermidis." Doctoral dissertation, University of Cincinnati, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1275920539

    Chicago Manual of Style (17th edition)