Examining Committee  
Dr. Yoshi Mine, Chair  
Dr. Keith Warriner, Advisor  
Dr. Jeffrey Farber, Advisory Committee Member   
Dr. Gisele LaPointe, Department Member  
  
TITLE: CONTRIBUTION OF THE PERSISTER STATE OF TOLERANCE OF ESCHERICHIA COLI 0157: H7 TO STRESSES ENCOUNTERED WITHIN THE FRESH PRODUCE CHAIN  
  
ABSTRACT:  
Escherichia coli  O157: H7 is a significant pathogen associated with fresh produce. The pathogen is not only noted for high virulence but the ability to survive for extended periods in the environment and through post-harvest processing.  The thesis examined the contribution of the persister (dormant) state within E. coli O157: H7 with regards to survival in soil, tolerance to ultraviolet light and chlorine sanitizers as well as revival  methods. Persister populations were selected for by challenging an exponentially growing culture of E. coli O157: H7 to ampicillin followed by an extended incubation period of up to 8 days. Upon addition of ampicillin the E. coli O157: H7 die-off in a multiphasic manner with culturable persisters emerging in Phase III and non-culturable in Phase IV.  The Phase III persisters were revived by simply removing the antibiotic pressure. However, persisters from Phase IV required extended incubation period which could be revived through acid-shock treatment.  The carbon utilization profile of persister cells was restricted compared to non-persister cells providing a means of differentiating the two populations. It was found persisters exhibited extended survival in soil microcosms and enhanced tolerance to both UV and chlorine. The study contributes to the knowledge of aspects of the persister state and its significance to food safety.