Christopher J Kristich, PhD
Assistant Professor
Microbiology and Molecular Genetics
Medical College of Wisconsin
Research Focus: Signal Transduction and Antibiotic Resistance in Gram-Positive Bacteria
PhD: University of Illinois, Urbana-Champaign (2002)
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Overview
Bacteria are remarkably adaptable. They detect a wide variety of physical and chemical signals in their environment, and use that sensory information as regulatory input to control their behavior and physiology – thereby maximizing their ability to survive and proliferate in the face of fluctuating environmental conditions. We use genetic, molecular, biochemical, and genomic experimental approaches to understand (1) the mechanisms by which Gram-positive bacteria sense internal and external stimuli, and (2) how these signaling systems control cellular processes in response to environmental conditions. Our goal is to understand all aspects of the sensory process: to define the signals that are sensed, to understand the signal transduction processes mechanistically, to identify the corresponding physiological or behavioral output, and to elucidate how that output – the product of the signal transduction processes – enhances the ability of the bacteria to survive and proliferate in their natural settings. Bacterial signal transduction processes play critical roles underpinning the relationship between bacteria and human hosts in both healthy and disease states. For example, signal transduction mediates adaptation of bacteria to different niches within the host during colonization; influences the transition from benign co-existence to a pathogenic condition; and allows the bacteria to tolerate toxic antimicrobial challenges that would otherwise eradicate them. Therefore, we approach problems of bacterial signal transduction in the context of basic bacterial physiology, host-microbe interactions, and microbial pathogenesis, with the goal of understanding how fundamental bacterial signaling processes serve to shape the outcome of interactions with human hosts and the environment.
Research Summary
The bacterium Enterococcus faecalis is a Gram-positive member of the normal human intestinal tract. Despite this, association of enterococci with humans is not always benign – for the last 20 years, enterococci have been (and remain today) among the three most common causes of hospital-acquired infections. The success of E. faecalis as a significant hospital-acquired pathogen is, at least in part, a consequence of its remarkable intrinsic resistance to an impressive variety of toxic antimicrobial agents, including widely used antibiotics. Intrinsic resistance of E. faecalis to specific classes of antimicrobials – those that are active against the bacterial cell-envelope – is especially important in the context of hospital-acquired enterococcal infections. For example, intrinsic resistance to detergents found in the intestinal emulsifying agent, bile, facilitates enterococcal colonization of the intestine, an important first step which usually precedes the onset of hospital-acquired infections. Furthermore, intrinsic resistance of E. faecalis to broad-spectrum cephalosporin antibiotics, which prevent bacterial cell-wall crosslinking in susceptible bacteria, enables E. faecalis to multiply to abnormally high intestinal cell densities when the ecological balance of the normal intestinal flora is disrupted in patients undergoing cephalosporin therapy – a known risk factor for enterococcal infection. However, despite the importance of intrinsic antibiotic resistance exhibited by E. faecalis, the genetic and molecular basis of this resistance remains poorly understood. Our research addresses this problem.
We have identified signal transduction pathways in E. faecalis that are required for its intrinsic resistance to various cell-envelope-active antimicrobials, including bile and cephalosporin antibiotics. Thus, these signaling systems are critical for the success of E. faecalis as an opportunistic pathogen. We are using a variety of approaches to probe the functions of these signaling systems at the molecular level, to understand how the systems are integrated with each other to produce the antimicrobial-resistant phenotype, and to determine how these systems promote enterococcal colonization of the intestinal tract and the onset of hospital-acquired infections. To facilitate our research, we have successfully developed a collection of critical genetic tools that enable efficient genetic analysis of E. faecalis, including counterselectable markers, conjugative delivery systems for allelic exchange, and tools for random and efficient transposon mutagenesis, among others. Armed with these essential tools, we are well-positioned to make rapid progress on important problems in enterococcal biology, with the long-term goal of developing new strategies for preventing or otherwise treating intractable infections caused by multi-antibiotic-resistant enterococci.
Scanning-electron micrographs of E. faecalis cultured under conditions in which the cells experience envelope stress. (A) Wild-type E. faecalis cells are intact and exhibit typical enterococcal morphology, indicating they are fully capable of withstanding the imposed stress. (B) Mutant E. faecalis cells lacking a key signal transduction protein often exhibit severe morphological defects, such as the loss of envelope integrity that is reflected by the collapsed cell on the right-hand side, indicating that their ability to withstand envelope stress is comprised.
Recent Publications
Kristich CJ, Chandler JR, Dunny GM. Development of a host-genotype-independent counterselectable marker and a high-frequency conjugative delivery system and their use in genetic analysis of Enterococcus faecalis. Plasmid. 2007 Mar;57(2):131-44. Epub 2006 Sep 22.
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Kristich CJ, Wells CL, Dunny GM. A eukaryotic-type Ser/Thr kinase in Enterococcus faecalis mediates antimicrobial resistance and intestinal persistence. Proc Natl Acad Sci U S A. 2007 Feb 27;104(9):3508-13. Epub 2007 Feb 20.
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Kristich CJ, Manias DA, Dunny GM. Development of a method for markerless genetic exchange in Enterococcus faecalis and its use in construction of a srtA mutant. Appl Environ Microbiol. 2005 Oct;71(10):5837-49.
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Erlandsen SL, Kristich CJ, Dunny GM, Wells CL. High-resolution visualization of the microbial glycocalyx with low-voltage scanning electron microscopy: dependence on cationic dyes. J Histochem Cytochem. 2004 Nov;52(11):1427-35.
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Kristich CJ, Ordal GW. Analysis of chimeric chemoreceptors in Bacillus subtilis reveals a role for CheD in the function of the McpC HAMP domain. J Bacteriol. 2004 Sep;186(17):5950-5.
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Kristich CJ, Li YH, Cvitkovitch DG, Dunny GM. Esp-independent biofilm formation by Enterococcus faecalis. J Bacteriol. 2004 Jan;186(1):154-63.
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Kristich CJ, Glekas GD, Ordal GW. The conserved cytoplasmic module of the transmembrane chemoreceptor McpC mediates carbohydrate chemotaxis in Bacillus subtilis. Mol Microbiol. 2003 Mar;47(5):1353-66.
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Kristich CJ, Ordal GW. Bacillus subtilis CheD is a chemoreceptor modification enzyme required for chemotaxis. J Biol Chem. 2002 Jul 12;277(28):25356-62. Epub 2002 May 13.
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Kirby JR, Kristich CJ, Saulmon MM, Zimmer MA, Garrity LF, Zhulin IB, Ordal GW. CheC is related to the family of flagellar switch proteins and acts independently from CheD to control chemotaxis in Bacillus subtilis. Mol Microbiol. 2001 Nov;42(3):573-85.
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Kirby JR, Saulmon MM, Kristich CJ, Ordal GW. CheY-dependent methylation of the asparagine receptor, McpB, during chemotaxis in Bacillus subtilis. J Biol Chem. 1999 Apr 16;274(16):11092-100.
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Kirby JR, Kristich CJ, Feinberg SL, Ordal GW. Methanol production during chemotaxis to amino acids in Bacillus subtilis. Mol Microbiol. 1997 May;24(4):869-78.
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Contact Information
Email: ckristich@mcw.edu
Phone: 414-955-4141
Room: TBRC C3930