Kimberly Jefferson , Ph.D.
Assistant Professor

Phone: (804) 828-9699
Dept. Fax: (804) 828-9946
e-mail: kkjefferson@vcu.edu

Address:
Department of Microbiology & Immunology
Virginia Commonwealth University
P.O. Box 980678
1101 East Marshall Street, Sanger Hall 6-040
Richmond, VA 23298-0678

Lab Web Page

Professional Experience

• B.S., 1992, Virginia Tech, Blacksburg, VA
• M.S., 1994, Virginia Tech
• Ph.D., 2001, University of Virginia, Charlottesville, VA
• Post-doc, 2001-2003, Harvard Medical School & Brigham & Women's Hospital
• Instructor in Medicine 2003-2005 Harvard Medical School & Brigham & Women's Hospital

Research Interests:

Our surroundings are constantly changing and consequently, the ability to adapt is a fundamental component of life.  When bacteria sense alterations in their environmental milieu, they adapt through the highly developed orchestration of gene expression. My particular area of interest within the realm of pathogenic bacterial physiology and adaptive gene expression is the process of switching from an independent, free-floating existence to a community-based, surface-associated mode of growth known as a biofilm.  Bacterial biofilm formation is a key determinant in the outcome of certain infections because bacteria that exist in this state are considerably more resistant to phagocytosis and to antimicrobial chemotherapy than their genotypically equivalent free-floating counterparts. In fact, biofilms can tolerate antibiotic concentrations 10-10,000-fold higher than those required to inhibit growth of free-floating bacteria. 

Patient hospitalization often involves the use of inserted medical devices, which can lead to the iatrogenic development of biofilm-related infections. Catheters and other medical devices breach the skin or mucosal barrier and serve as an ideal surface for bacterial adherence. The staphylococci are implicated in nosocomial infections, such as bloodstream and ventilator-associated infections, more frequently than any other bacterial species. When S. aureus assumes the biofilm phenotype, these infections are often extremely difficult to treat. The infection may fail to respond to antibiotic therapy or it may initially respond only to relapse weeks or months later. In such cases, invasive treatments, such as surgical removal and replacement of the infected tissue or device, may be required. 

Project #1 Antibiotic resistance in S. aureus biofilms. The urgent need to develop a more effective means to treat such infections calls for a thorough understanding of gene expression as it relates to the biofilm mode of growth, and is the inspiration behind our research. One of our projects investigates the molecular and genetic basis for elevated antibiotic tolerance within biofilms. We discovered that, due to constraints on convective forces imparted by the clustering of bacteria, antibiotics penetrate biofilms relatively slowly (1). As a result of the decreased rate of transport, bacteria furthest from the source of the antibiotic are exposed gradually, and we hypothesize that this affords them the opportunity to mount an adaptive response by altering the expression of key genes. We used S. aureus microarrays to monitor changes in global gene expression in biofilms following vancomycin treatment, and found decreased expression of genes involved in transport, and increased expression of genes involved in heat shock, stress, and cell wall synthesis in response to the drug. We plan to use genetic and molecular approaches to determine the role of some of these genes in biofilm resistance.   

Project #2 Regulation of exopolysaccharide production in S. aureus.  The second project in our lab aims at unraveling the relationship between environmental cues and the molecular switches that turn on production of the biofilm polysaccharide matrix. Culture conditions were designed to maximize bacterial growth and therefore tend to foster a planktonic, rather than the biofilm mode of growth. Biofilm formation in vitro can be induced by a number of environmental factors that mimic conditions likely to be encountered in vivo, including glucose availability, iron deprivation, and high osmolarity. In vivo and under in vitro conditions that promote biofilm elaboration, S. aureus produces a cell surface-associated b-1-6-linked polymer of N-acetyl-glucosamine (PNAG) also referred to as polysaccharide intercellular adhesin (PIA). PNAG/PIA promotes adhesion to surfaces and to other bacterial cells, and is the major component of the biofilm matrix (Fig 1). It is synthesized by four proteins encoded within the intercellular adhesin (ica) locus, a glucosyltransferase (IcaA) and its chaperone (IcaD), a de-acetylase (IcaB) and the IcaC protein, which is thought to be involved in secretion of the polymer.  Not only is PNAG/PIA critical for biofilm formation, but it also plays an important role in virulence. Presence of the ica locus is important for certain types of human infections and animal infection models (2). PNAG/PIA inhibits phagocytosis in the absence of antibody whereas anti-PNAG antibodies mediate opsonophagocytosis and have demonstrated promise as a vaccine candidate (2). Very recent evidence indicates that a number of unrelated bacterial pathogens, including E. coli, Yersinia pestis, Y. pseutuberculosis, and Bordetella pertussis, harbor ica homologues, and we have found that these species produce an exo-polysaccharide that is antigenically indistinguishable from S. aureus PNAG. In summary, PNAG/PIA has an important and multi-faceted role in biofilm formation and virulence and we aim to elucidate its regulation in order to form a basis for anti-biofilm therapy.

Fig. 1. Use of confocal microscopy to analyze PNAG/PIA. The intercellular adhesin (ica) locus in S. aureus encodes the proteins necessary for PNAG/PIA synthesis so ica-positive and ica-negative mutants were used as positive and negative controls.  A) the strong PNAG-producing S. aureus strain MN8m produces a thick, mature biofilm with microcolonies separated by channels for nutrient and oxygen flow B) the PNAG-negative S. aureus strain MN8Dica::tet forms a homogenous mat of bacteria that is easily removed by washing. The bacteria were stained with WGA-Green, which binds to PNAG/PIA and imaged by confocal microscopy. The bacterial cells are presented in red. Each bar segment represents 20 mm.

Project #3 Degradation of biofilms in bacterial vaginosis.  Bacterial vaginosis or BV is the most common vaginal disorder in women worldwide.  The infection occurs when the healthy vaginal lactobacilli are replaced by unhealthy anaerobes.  It can be treated with metronidazole but it frequently recurs or relapses.  BV is associated with a number of serious complications including an increase in the rates of HIV acquisition and transmission, preterm births, and pelvic inflammatory disease.  The anaerobes that cause the symptoms of BV, especially Gardnerella vaginalis, form a biofilm on the vaginal epithelium and we hypothesize that the biofilm phenotype is responsible for the chronic and relapsing nature of the infection.  Our goal is to isolate an enzyme that degrades G. vaginalis biofilms that could be used in conjunction with traditional antibiotic therapy to more effectively treat the infection.

Selected Publications:

1. Cerca N, K. K. Jefferson. (2008). Effect of growth conditions on poly-N-acetylglucosamine expression and biofilm formation in Escherichia coli. FEMS Microbiol Lett. Accepted for publication.

2. Cerca N, T. Maira-Litran, K.K Jefferson, M. Grout, D.A. Goldmann, G.B. Pier. (2007) Protection against Escherichia coli infection by antibody to the Staphylococcus aureus poly-N-acetylglucosamine surface polysaccharide. Proc Natl Acad Sci U S A. 104;7528.

3. Cerca N, K.K Jefferson, T. Maira-Litran, D.B. Pier, C. Kelly-Quintos, D.A. Goldmann, J. Azeredo, G.B. Pier. (2007) Molecular basis for preferential protective efficacy of antibodies directed to the poorly-acetylated form of staphylococcal poly-N-acetyl-{beta}-(1-6)-glucosamine. Infect Immun.

4. Patterson, J.L., P.H. Girerd, N.W. Karjane, K.K. Jefferson. (2007). Biofilm formation increases resistance of Gardnerella vaginalis to hydrogen peroxide and lactic acid. Amer J Obstet Gyn. 197(2):170.

5. Cerca N., Jefferson K. K. Pier  D. B., Maira-Litrán T., Kelly-Quintos C., Goldmann D. A., Azeredo J., and Pier  G. B. (2007). Molecular basis for preferential protective efficacy of antibodies directed to the poorly-acetylated form of staphylococcal poly-N-acetyl-b-(1-6)-glucosamine (PNAG). Infect Immun. 75(7):3406-13.

6. Cerca, N. , K. K. Jefferson, R. Oliveira, G. B. Pier, J. Azeredo. (2006) Comparative antibody-mediated phagocytosis of Staphylococcus epidermidis cells grown in a biofilm or in the planktonic state. Infect Immun 74(8):4849-55.

7. Jefferson K. K. and N. Cerca. (2006). Bacterial-bacterial cell interactions in biofilms: detection of polysaccharide intercellular adhesins by blotting and confocal microscopy. Methods Mol Biol. 341:119-26.

8. Jefferson K. K., D. A. Goldmann, and G. B. Pier. (2005). Use of confocal microscopy to analyze the rate of vancomycin-binding in Staphylococcus aureus biofilms. Antimicrob. Agents Chemother. 49(6): 2467-2473.

9. Cerca N., S. Martins, S. Sillankorva, K. K. Jefferson, G. B. Pier, R. Oliveira, J. Azeredo. (2005). Effects of growth in the presence of subinhibitory concentrations of dicloxacillin on Staphylococcus epidermidis and Staphylococcus haemolyticus biofilms. Appl Environ Microbiol. 71(12):8677-82.

10. Cerca N, S. Martins, F. Cerca, K. K. Jefferson, G. B. Pier, R. Oliveira, J. Azeredo. (2005). Comparative assessment of antibiotic susceptibility of coagulase-negative staphylococci in biofilm versus planktonic culture as assessed by bacterial enumeration or rapid XTT colorimetry. J Antimicrob Chemother. 56(2):331-6.

11. Kropec A., T. Maira-Litran, K. Jefferson, M. Grout, C. Kelly-Quintos, S. Cramton, F. Götz, D. A. Goldmann, G. B. Pier. (2005). Poly-N-acetyl glucosamine production in Staphylococcus aureus is essential for virulence in murine models of systemic infection. Infect. Immun. 73(10) 6868-6876.

12. Cerca N., Martins S., Cerca F., Jefferson K. K., Pier G. B., Oliveira R., Azeredo J.  (2005). Comparative assessment of the susceptibility of coagulase-negative staphylococcal cells in biofilm versus planktonic culture to antibiotic killing as assessed by bacterial enumeration or rapid XTT colorimetry. J. Antimicrob. Chemother. 56:331-336.

13. Jefferson K. K., D. B. Pier, D. A. Goldmann, and G. B. Pier. (2004). The teicoplanin-associated locus regulator (TcaR) and the intercellular adhesin locus regulator (IcaR) are transcriptional inhibitors of the ica locus in Staphylococcus aureus. J. Bacteriol. 186 (8): 2449-2456.

14. Jefferson K. K., S. E. Cramton , F. Götz, G. B. Pier. (2003). Identification of a 5-nucleotide sequence that controls expression of the ica locus in Staphylococcus aureus and characterization of the DNA-binding properties of IcaR. Mol. Microbiol. 48(4):889-899.

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Date Last Modified: 07/10/2008
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