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Investigating the Spread of Antimicrobial Resistance: Mechanisms of Extracellular DNA Transport and Transfer

Speaker: Helen Nguyen, University of Illinois at Urbana-Champaign
Series: CEE Departmental Seminars
Location: Bowen Hall Auditorium
Date/Time: Monday, October 4, 2010, 4:30 p.m. - 5:30 p.m.


The use of antimicrobials in agriculture, aquaculture, and daily life is being reconsidered because of the multi-drug resistant infections fostered by overdosed antimicrobials and the possible adverse effects from antibiotic resistance genes on agriculture soil and other affected environments. Antibiotic resistance genes from antibiotic resistant bacteria selected by overdosed antimicrobials in the animal industry might get into the agricultural soil by manure waste land application. Horizontal gene transfer can spread antibiotic resistance; therefore, a more fundamental understanding of what conditions can lead to more frequent transfers is needed.  Quartz crystal microbalance with dissipation (QCM-D) was used to study extracellular DNA adsorption and the conformation of the adsorbed DNA on silica and natural organic matter (NOM) surfaces. Gene transfer was assessed under the same conditions using natural transformation of chromosomal and plasmid DNA into soil bacteria Azotobacter vinelandii to explore the relationships among environmental parameters, DNA adsorption, and the efficiency and rate of gene transfer for pure cultures. Experimental results indicate that solution ionic composition, such as calcium concentration and natural organic matter in groundwater, influence the amount of DNA that is adsorbed and protected from enzymatic degradation, but did not have a strong influence on natural transformation. The presence of oxytetracycline in solution or in adsorbed form at environmentally-relevant concentrations also did not have a strong influence natural transformation of A. vinelandii. In addition, we found that oxytetracycline adsorbed to clay particles lost its ability to inhibit A. vinelandii growth. This work suggests that adsorbed DNA is fully bioavailable and could be an important reservoir for environmental gene transfer.


Helen Nguyen holds a B.S. with Honors in Geology (Ivan Franko National University of L'viv, Ukraine, 1995), an M.S. in Earth and Environmental Science (University of Illinois at Chicago, 2000), an M.S. in Environmental Engineering (Johns Hopkins University, 2004), and a Ph.D. in Environmental Engineering (Johns Hopkins University, 2005). Dr. Nguyen joined the faculty of the Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign in November 2006.
Prior to joining University of Illinois, Dr. Nguyen was a Gaylord Donnelley Environmental Postdoctoral Fellow at Yale University.  Dr. Nguyen is the recipient of the 2006 AEESP/CH2M Hill Outstanding Dissertation Award, 2010 NSF CAREER award, and 2010 ASCE/EWB Sustainable Development Award for advising a EWB team that develops a sustainable engineering solution that explores innovative ways of effectively capturing and utilizing resources.

Dr. Nguyen's research goal is to develop conceptual models that aid in assessing the human and ecological risks associated with biological contaminants in subsurface environments and water treatment systems. Specific areas of interest are waterborne pathogen removal for water and wastewater treatment, and fate and transport of antibiotic resistant bacteria in subsurface environment. Dr Nguyen's group applies sophisticated experimental techniques from the field of molecular biology, microbiology, colloidal/interfacial chemistry, and environmental engineering.