P-027. Fate of Foodborne Pathogens in Expelled Fecal Pellets of a Ciliated Protozoan

C. T. Pannell1, M. T. Brandl2, B. Goodson1, M. J. M. Wells1, S. G. Berk1;
1Tennessee Technological Univ., Cookeville, TN, 2USDA, Albany, CA.

Background: The 2006 E. coli outbreak from spinach prompted us to determine whether survival of E. coli O157:H7 and Salmonella typhimurium is enhanced in association with ciliated protozoa, commonly found on fresh produce. Our previous work demonstrated that Salmonella enterica survived longer in vesicles (fecal pellets) released from the ciliate, Tetrahymena sp., than did free S. enterica cells. Methods: For the present study E. coli O157:H7 (Ec) and S. typhimurium (St) were fed separately to the ciliate, Tetrahymena sp., and observed in released ciliate fecal pellets. A direct microscopic assay (BacLight) determined the % viable bacteria in pellets and free in suspensions up to 2 weeks. The fate of bacteria in expelled pellets was further examined by adding spinach extract and nalidixic acid to the pellet suspensions to determine whether such bacteria were able to grow in expelled pellets. Additionally, pellets and free bacteria were dried in a chamber at ~ 2-4 % relative humidity and tested 4 weeks for viable bacteria in the samples. Analysis of variance and Tukey’s multiple comparisons test were used to analyze data. Results: For both Ec and St, a higher percentage of bacteria was viable in pellets (~100% of bacterial cells) than for free pathogens over 2 weeks in the buffer. Addition of spinach extract showed that both Ec and St could grow and escape the pellets in 4 hr. No difference in viability in pellets was observed between Ec or St compared with free Ec and St when dried, except at 4 weeks with St, when the percentage of viable cells was higher for St in pellets. Conclusion: Release of pathogens in ciliate pellets can enhance their survival in a liquid medium and permit subsequent growth of pathogens. Such microbial interactions may have significant implications for the produce industry.