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United States Department of Agriculture

Agricultural Research Service

Research Project: Biology and Control of Human Pathogens on Fresh Produce

Location: Produce Safety and Microbiology Research

Title: Survival characteristics of diarrheagenic Escherichia coli pathotypes and Helicobacter pylori during passage through the free-living ciliate, Tetrahymena sp.

Authors
item Smith, Charlotte -
item Berk, Sharon -
item Brandl, Maria
item Riley, Lee -

Submitted to: FEMS Microbiology Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 27, 2012
Publication Date: July 3, 2012
Citation: Smith, C.D., Berk, S.G., Brandl, M., Riley, L.W. 2012. Survival characteristics of diarrheagenic Escherichia coli pathotypes and Helicobacter pylori during passage through the free-living ciliate, Tetrahymena sp. FEMS Microbiology Ecology. 82:574-583.

Interpretive Summary: Epidemiologic and environmental studies of the occurrence and treatment of enteric bacteria overlook the fact that in the natural environment these pathogens exist in the same niches as free-living protozoa, including ciliates such as Tetrahymena. Ciliates prey on bacteria in water and waste water systems. Compartmentalization of ingested material(including bacteria)in the food vacuoles of Tetrahymena and its egestion in the fecal pellet has been described and the survival of Salmonella enterica and E. coli O157:H7 in such fecal pellets has been reported. Here we provide evidence that all of the six major pathotypes of diarrheagenic E. coli are able to survive digestion by this ciliate and describe the ultrastructure of these pathotypes in Tetrahymena food vacuoles and fecal pellets. An enhanced understanding of the survival of pathogenic E. coli in protozoa should provide a foundation for future studies on disinfection methods to improve microbial quality of water.

Technical Abstract: Ciliates prey on bacteria in water and waste water systems. Compartmentalization of ingested material (including bacteria) in the food vacuoles of Tetrahymena and its egestion in the fecal pellet has been described and the survival of Salmonella enterica and E. coli O157:H7 in such fecal pellets has been reported. It is unclear whether the various pathotypes of E. coli interact with Tetrahymena in a fashion similar to that of the EHEC strain O157:H7. Using viability assays, we have obtained evidence that all six diarrheagenic pathotypes of E. coli not only evade digestion but remain viable and replicate within Tetrahymena fecal pellets. This suggests a possible role for Tetrahymena-E. coli interactions and more specifically for fecal pellets in the survival and dissemination of pathogenic E. coli in the environment. We observed by EM that the structure of the pellet sac is relatively fragile and allows for the escape of bacterial cells during multiplication. Also, the fecal pellets were sticky, as evidenced by their adherence into large flocs or to Tetrahymena cells. This adhesive property may play a role in the behavior of human pathogens in water systems because entrapment of bacterial prey in the adhesive floc may increase their occurrence in aquatic environments.

Last Modified: 12/27/2014
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