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.

Antimicrobial treatments using light and plant derived compounds.

Food safety is a global issue with significant implications for human health. The World Health Organization reports that unsafe food results annually in the illnesses of at least 2 billion people worldwide with many thousands of deaths. Chemical methods used to disinfect food may protect against the spread of foodborne bacteria, but such practices put selective pressure on bacteria to develop countermeasures that are often heritable. Consumers in Europe and Britain are concerned that the use of chemical agents creates both microbiological and chemical food safety hazards by selecting for antibiotic resistance and generating potential carcinogenic compounds. The research conducted by the Matthews’ laboratory will provide the proof of concept for the photoinactivation treatment of meat and poultry, fruits and vegetables to control foodborne bacteria and enhance microbial safety. The photosensitizers used will be natural compounds—sodium copper chlorophyllin, curcumin, and riboflavin —that will be acceptable by consumers (provide a “clean label”) and government agencies and are not known to be associated with contributing to antimicrobial resistance. The umbrella goal of the research is to provide the science to support the effective application of photoinactivation treatment of food derived from animals and plants to improve microbiological safety of those foods.