Karl R. Matthews, Ph. D.


Research Interest

The microbial safety of food impacts consumers nationally and internationally.  My research uses tools of biotechnology to address questions of survival and virulence of foodborne pathogens.  More so than many other disciplines food microbiology is in continual flux; new pathogens emerge, long recognized pathogens re-emerge as problems, and consumer demands change.  Research emphasis is in the areas of microbial safety of fresh fruits and vegetables and antimicrobial resistance of foodborne pathogens.

Interaction of enteric foodborne pathogens with plants – Regulation of plant defense system

Understanding the interaction of foodborne pathogens including Escherichia coli O157:H7 and Salmonella with leafy greens (e.g., lettuce, spinach) is important in the development of strategies to control foodborne illness linked to the consumption of fresh and fresh-cut fruits and vegetables.  Numerous factors can influence contamination of produce, including the use of manure as a fertilizer; contaminated agricultural water; hygiene practices of workers in the field, packinghouse and processing plant.  Challenges exist with respect to devising and implementing measures to control and prevent contamination.  A significant knowledge gap exits in understanding how bacterial cell surface moieties affect adherence of a enteric pathogen to plant tissue and how those cell surface moieties influence activation of a plants defense systems.
Our research is using Arabidopsis thaliana to initially determine whether specific cell surface moieties of enteric bacteria stimulate the plants defense system. Isogenic mutants of E. coli O157:H7 and Salmonella which lack key cell surface moieties are used in these experiments. Using Arabidopsis ensures that experimental conditions can be achieved.  The construction of lettuce and spinach lacking genes involved in regulation of pathways of the plants defense system is on-going and will demonstrate the importance of bacterial cell surface moieties in persistence of bacteria on plant tissue.  We will construct lettuce impaired in plant defense and a line where the plant defense response gene is fused to a reported.  Both lines will be similar to the Arabidopsis lines being used.

Development of “Green Nanoparticles” to enhance the microbial safety of food.

We envision the development of a “green nanoparticle” wash treatment with the capability of the elimination of pathogenic bacteria and reduction of total bacteria populations during minimal processing of fresh fruits and vegetables. The proposed treatment step will employ suspensions of cationic, preservative-loaded, antimicrobial peptide-decorated nanoparticles, where washing or immersion in a nanoparticle suspension, possibly in conjunction with the application of a mild electric field, can flocculate and destroy pathogenic bacteria on fresh produce immediately prior to packaging. The exceptional potency of the peptide-enhanced nanoparticles derives from the combined synergistic action of cationic chitosan nanoparticles, encapsulated and surface-attached antimicrobial peptides and applied electric fields on the bacterial cell membrane to cause pathogen lysis. The novelty of the proposed research centers on the effective delivery of multiple antimicrobials which are required to positively eliminate both Gram-positive and Gram-negative foodborne pathogens. 

Since chitosan, the nanoparticle base material, is an edible, biocompatible polymer, and the peptides are well-known preservatives, the health risk of introducing nanoparticles of such materials into food is minimal and investigation of GRAS (Generally Recognized As Safe) components should result in a faster transition to a working prototype. Moreover, the components used are not know to elicit organoleptic changes in foods. The proposed system is a “green technology” because it utilizes edible, environmentally benign, and naturally abundant materials. If used in conjunction with conventional antimicrobial treatments, the new method has the potential to reduce the concentrations of chemical preservatives and energy intensity required for pathogen lysis from current levels.