DEVELOPMENT OF A NOVEL MULTILOCUS SEQUENCE TYPING (MLST) SUBTYPING STRATEGY FOR TRACKING THE FARM-TO-FORK TRANSMISSION OF ESCHERICHIA COLI O

Escherichia coli O157:H7 is foodborne pathogen that is responsible for an estimated 73,000 illnesses each year within the United States. This organism causes diarrhea that may become bloody, and approximately 5-15% of cases progress into a life-threatening condition called haemolytic uremic syndrome. E. coli O157:H7 can be isolated from the intestinal tract of cattle, and is transmitted to humans when contaminated fecal material or cattle hides come into contact with food materials. Most foodborne infections are the result of contaminated ground beef, however a growing number of outbreaks are linked to fresh produce such as lettuce and spinach. As part of an epidemiologic investigation, DNA-based methods are used to track the spread of specific strains of E. coli O157:H7 from farm-to-fork. Only once the route(s) of transmission are defined can effective intervention strategies be implemented to stop this spread. For E. coli O157:H7, this is currently done using a technique called pulsed field gel electrophoresis (PFGE). While PFGE has proven effective this method suffers from many limitations including the length of the protocol, technical expertise needed, and the ambiguous data that sometimes results. Techniques that differentiate between strains of E. coli O157:H7 based upon differences in DNA sequence, such as multilocus sequence typing (MLST), have potential to be more rapid and cost effective. The development of such methods has suffered due to the large similarity found within the DNA of different E. coli O157:H7 strains. We hypothesize that sequencing the DNA of a large number of E. coli O157:H7 strains will identify genomic targets for discriminating between different strains and lead to the development of a tracking method that can complement or even replace PFGE. Once we have developed an MLST approach, we will test its effectiveness in microbial source tracking within beef processing facilities. This research therefore has the potential to improve the safety of our food supply by improving our ability to rapidly trace the source of contamination and to apply control points to break this chain of transmission.