Leafy greens such as spinach have been the object of several recent food-borne pathogen outbreaks. The purpose of this study was to isolate bacteria spinach epiphytic bacteria that inhibit growth of E. coli O157:H7, which we describe as antagonism. The mechanism of antagonism was investigated and we attempted to improve the antagonistic potential in vitro and on spinach leaves when cellobiose, a carbon source utilized by the antagonists but not E. coli O157:H7, was added.
There were larger culturable populations of bacteria on the leaves of savoyed cultivars compared to flat. From the isolated colonies, 47 displayed antagonism towards E.coli O157:H7, and were identified as members of 11 different genera and sixteen species. A representative isolate from each species was evaluated for three possible mechanisms of antagonism: acid production, secretion of an inhibitory compounds or secreted protease. The majority (14/16) produced at least a moderate level of acid. Two of these strains, Paenibacillus polymyxa and Pseudomonas espejiana, were found to secrete a non- protease antagonistic compound.
These antagonists varied in their reduction of E.coli O157:H7 numbers in vitro, but all significantly reduced numbers in 48 hours of co-culturing in nutrient rich media. Five antagonists resulted in a significant reduction in E.coli O157:H7 populations when co-cultured on spinach leaves. Application of cellobiose did not improve the amount of antagonism in vitro or on the leaf surface after 24 hours. / Master of Science
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/43364 |
| Date | 07 July 2010 |
| Creators | Tydings, Heather Anne |
| Contributors | Food Science and Technology, Ponder, Monica A., Boyer, Renee R., Falkinham, Joseph O. III |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Thesis |
| Format | application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
| Relation | Tydings_HA_T_2010.pdf |
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