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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: The Salmonella transcriptome in lettuce and cilantro soft rot reveals a niche overlap with the animal host intestine

Authors
item Goudeau, Danielle
item Parker, Craig
item Zhou, Yaguang
item Sela, Shlomo -
item Kroupitski, Yulia -
item Brandl, Maria

Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 20, 2012
Publication Date: January 1, 2013
Citation: Goudeau, D.M., Parker, C., Zhou, Y., Sela, S., Kroupitski, Y., Brandl, M. 2013. The Salmonella transcriptome in lettuce and cilantro soft rot reveals a niche overlap with the animal host intestine. Applied and Environmental Microbiology. 79:250-262.

Interpretive Summary: Fresh vegetables have been recurrently associated with salmonellosis outbreaks and Salmonella contamination of retail produce has been correlated positively with the presence of soft rot disease. We observed that population sizes of Salmonella enterica Typhimurium SL1344 increased 56-fold when inoculated alone onto cilantro leaves versus 2,884-fold when co-inoculated with Dickeya dadantii, a prevalent pathogen that macerates plant tissue. A similar trend in S. enterica populations was observed in soft-rotted lettuce leaves. Gene expression analysis in S. enterica cells that colonized D. dadantii-infected lettuce and cilantro leaves revealed a clear shift toward anaerobic metabolism and utilization of nutrients that are available due to degradation of plant cells by the plant pathogen. Twenty nine percent of the genes that were upregulated in cilantro macerates were previously observed to increase in expression also in the chicken intestine. Among those, the operons for ethanolamine and propanediol utilization, as well as for synthesis of cobalamin, a co-factor in these pathways, were the most highly and broadly upregulated in lettuce and cilantro lesions. Anaerobic conditions and the utilization of nutrients in the macerated plant tissue that are present also in the animal intestine indicate a niche overlap that may explain the high adaptation of S. enterica to soft rot lesions, a common post-harvest plant disease.

Technical Abstract: Fresh vegetables have been recurrently associated with salmonellosis outbreaks and Salmonella contamination of retail produce has been correlated positively with the presence of soft rot disease. We observed that Salmonella enterica Typhimurium SL1344 grows to 50-fold greater populations in the presence of Dickeya dadantii, a prevalent pathogen that macerates plant tissue. A similarly behavior was observed in soft-rotted lettuce leaves. Gene expression analysis in S. enterica cells that colonized D. dadantii-infected lettuce and cilantro leaves revealed a clear shift toward anaerobic metabolism and utilization of nutrients that are available due to degradation of plant cells by the plant pathogen. Twenty nine percent of the genes that were upregulated in cilantro macerates were previously observed to increase in expression also in the chicken intestine. Among those, the operons for ethanolamine and propanediol utilization, as well as for synthesis of cobalamin, a co-factor in these pathways, were the most highly and broadly upregulated. Anaerobic conditions and the utilization of nutrients in the macerated plant tissue that are present also in the human and animal hosts indicate a niche overlap that may explain the high adaptation of S. enterica to soft rot lesions, a common post-harvest plant disease.

Last Modified: 9/1/2014
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