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United States Department of Agriculture

Agricultural Research Service

Research Project: MICROBIAL ECOLOGY AND SAFETY OF FRESH PRODUCE

Location: Environmental Microbial and Food Safety Laboratory

Title: Effect of spinach cultivar and bacterial adherence factors on survival of Escherichia coli O157:H7 on spinach leaves

Authors
item Macarisin, Dumitru
item Patel, Jitu
item Bauchan, Gary
item Giron, Jorge -
item Ravishankar, Sadhna

Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 8, 2013
Publication Date: November 1, 2013
Citation: Macarisin, D., Patel, J.R., Bauchan, G.R., Giron, J., Ravishankar, S. 2013. Effect of spinach cultivar and bacterial adherence factors on survival of Escherichia coli O157:H7 on spinach leaves. Journal of Food Protection. 76(11):1829-1837.

Interpretive Summary: Numerous Escherichia coli O157:H7 outbreaks have been associated with contaminated fresh produce. Cultivar-dependent leaf structure and cellular appendages such as curli fimbriae may influence E. coli O157:H7 survival on spinach leaves. We evaluated the effect of curli and cellulose in E. coli O157:H7 survival on four organic spinach cultivars: Emilia, Lasio, Space, and Waitiki. E. coli O157:H7 isolates and their mutants were spot-inoculated (approximately 5 million/leaf) on spinach leaves of 6 week old spinach plants. Surviving E. coli O157:H7 populations on spinach leaves were determined by plating onto Sorbitol MacConkey agar. Leaf morphology was evaluated by scanning electron microscopy. E. coli O157:H7 persistence on spinach was significantly affected by cultivar and strain phenotypic characteristics, specifically expression of curli fimbriae. Leaf blade roughness and stomata density also significantly affected E. coli O157:H7 persistence on spinach leaves. Cultivar Witiki, with the highest leaf roughness supported significantly higher E. coli O157:H7 populations compared to other cultivars. These two morphological characteristics of spinach cultivar should be taken into consideration in developing intervention strategies to enhance microbial safety in fresh produce industry. This informatiion should be useful to other scientists, the produce industry and to regulatory agencies.

Technical Abstract: Similarly to phytopathogens and epiphytic microorganisms, human bacterial pathogens have been shown to colonize on plant phylloplane. Along with environmental variables such as temperate, UV light, relative humidity, etc., plant cultivar and specifically the leaf blade morphological characteristics may affect the persistence and survival of enteropathogens on fresh produce surfaces. The current study was conducted to evaluate the effect of cultivar-dependent leaf topography and the role of strain phenotypic characteristics on the E. coli O157:H7 persistence on organic spinach leaves. Spinach cultivars Emilia, Lasio, Space and Witiki were experimentally contaminated with a foodborne E. coli O157:H7 isolate EDL933 and its isogenic mutants deficient in cellulose (EDL933deltabcsA), curli (EDL933deltacsgA), and both curli and cellulose (EDL933deltacsgA/deltabcsA) production. Leaves of 6 week old plants were inoculated with 6.5 log CFU/leaf in BL-2 growth chamber. At 0, 1, 7, and 14 days, surviving E. coli O157:H7 populations were determined by plating on selective media and verified by laser scanning confocal microscopy. Leaf morphology was evaluated by low temperature and variable pressure scanning electron microscopy. E. coli O157:H7 persistence on spinach was significantly affected by cultivar and strain phenotypic characteristics, specifically expression of curli fimbriae. Curli-deficient E. coli O157:H7 strains were more susceptible to the effect of cultivar than curliated strains. Leaf blade roughness and stomata density appeared to be the major factors determining differential attachment and persistence of E. coli O157:H7 on spinach. Cultivar Witiki with highest leaf roughness supported significantly higher E. coli O157:H7 populations compared to other cultivars. These two morphological characteristics of spinach cultivar should be taken into consideration in developing intervention strategies to enhance microbial safety in fresh produce industry.

Last Modified: 10/25/2014
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