Gary M. Dunny, Ph.D.

Research Interests:

My laboratory studies the regulation of expression of genetic transfer functions and the regulation of virulence in gram positive bacteria. We are especially interested in regulatory mechanisms involving cell-cell signaling by peptide mating pheromones. We also study several novel intracellular regulatory RNA molecules that control expression of genes involved in conjugative plasmid transfer. The current research activity of the lab is comprised of the three specific projects listed below, each of which is supported by a grant from the NIH.

Supplementary Grant Information July 2009

Project 1: Genetic Functions of an Enterococcal R factor. Enterococci are gram positive bacteria commonly found in the intestinal tract of healthy individuals. Recently they have received increasing attention because they are one of the most common cause of hospital-acquired infections. They also serve as a major vector for the spread of antibiotic resistance determinants. In this project, we are studying the mechanism by which conjugative transfer from a donor cell of an antibiotic resistance plasmid called pCF10 is stimulated by a peptide pheromone produced by the recipient cell. The specific aims of the project include analysis of the mechanism of pheromone synthesis, the mechanism of pheromone sensing, and the DNA processing and transfer events that occur as a result of pheromone induction. We employ a combination of genetic and molecular techniques to address these questions.

Link to Electron Micrograph of mating bacteria

Selected Recent Publications:

• Bae T, Kozlowicz B, Dunny GM. 2002. Two targets in pCF10 DNA for PrgX binding; their role in production of Qa and prgX mRNA and in regulation of pheromone-inducible conjugation. J Mol Biol 315(5):995-1007. Abstract
  
• Antiporta MH, Dunny GM. 2002. ccfA, the genetic determinant for the cCF10 peptide pheromone in Enterococcus faecalis OG1RF. J Bacteriol 184(4):1155-62.
  
• Dunny GM. 2002. Group effort in toxin synthesis. Nature 415(6867):33-34.
  

 

Project 2: Role of Cell Wall Components in Enterococcal Endocarditis. This research, carried out in collaboration with Dr. Schlievert, is directed toward analysis of cell wall components of Enterococcus faecalis that play important roles in the pathogenesis of enterococcal endocarditis. One major finding from the research carried out thus far on this project is that the resistance plasmid pCF10 increases the virulence of strains in which it resides. A major pCF10-encoded virulence factor is the Aggregation Substance protein Asc10. In laboratory medium, expression of Asc10 by pCF10-carrying cells is induced by a peptide pheromone cCF10, excreted by potential conjugative recipient cell. However, expression of the protein can be induced in mammalian hosts, probably by two different factors. Progress in our own laboratory, along with the general development of technology for microbial genomic analysis and protein structure analysis, have made it feasible to begin X-ray crystallographic structural analysis of Asc10, as well as comparative microarray analysis of the expression of pCF10 genes and enterococcal chromosomal genes in mammalian hosts.

Link to Electron Micrograph of bacteria expressing virulence proteins

Supplemental information for Hirt et al. (PDF)

Microarray final (Microsoft Excel Document)

Microarray final (Graph-JPEG)

Project 3: Role of Biofilm Characterization
The enterococci are frequent causes of opportunistic infections, particularly among hospital patients. The medical significance of these organisms is due in part to their inherent and acquired resistance to antimicrobial chemotherapeutic agents, and to their ability to transfer genetic determinants for resistance to other pathogens. It is clear that biofilm formation contributes significantly to the medical problems caused by enterococci. Endocarditis, the most serious enterococcal infection, also involves surface colonization and growth on heart valves in a biofilm-like state. These studies of enterococcal physiology and genetics as they relate to the biofilm state will enhance our understanding of enterococcal disease pathogenesis.

The specific aims of this project seek to identify the E. faecalis genetic determinants required for biofilm formation using microarray and genetic screening methods. Interesting genes are being studied using reporter gene constructs to monitor expression in biofilms. At the same time the cellular and molecular structure of E. faecalis biofilms is being visually analyzed using high resolution scanning electron microscopy and cryofixation technology .

Selected Recent Publications:

• Hirt H, Schlievert PM, Dunny GM. 2002. In vivo induction of virulence and antibiotic resistance transfer in Enterococcus faecalis mediated by the sex pheromone-sensing system of pCF10. Infect Immun 70(2):716-23.
  
• Waters CM, Dunny GM. 2001. Analysis of functional domains of the Enterococcus faecalis pheromone-induced surface protein aggregation substance. J Bacteriol 183(19):5659-67.
  
• McCormick, J.K., Hirt H., Waters, C.M., Tripp, T.J., Dunny, G.M., Schlievert P.M. 2001. Antibodies to a surface-exposed, N-terminal domain of aggregation substance are not protective in the rabbit model of Enterococcus faecalis infective endocarditis. Infect Immun 69(5):3305-14.
  
• Patrick M. Schlievert, Olivia N. Chuang, Marnie L. Peterson, Suzanne M. Grindle, Laura C. Case, Gary M. Dunny. Reduction of Enterococcus faecalis Endocarditis with IgG Fab Fragments that Interfere with Aggregation Substance-Mediated Immune Response Suppression. In Review
  

 

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The Dunny lab: 2007
Smart, happy and hardworking!

Email current graduate students for specific information about their project and about working in the Dunny lab:

Olivia Chuang (6th year student) chua0041@umn.edu

Katie Ballering (5th year student) balle028@umn.edu

Heather Haemig (post-doctoral) hrode001@umn.edu

Chris Johnson (3rd year student) john5771@umn.edu

Laura Case (3rd year student) case0149@umn.edu

Kristi Frank (post-doctoral) fran0616@umn.edu

Aaron Barnes (3rd year MD/PhD student) barnesa@umn.edu