Location: Produce Safety and Microbiology ResearchTitle: Genes ycfR, sirA and yigG contribute to the surface attachment of Salmonella enterica Typhimurium and Saintpaul to fresh produce Author
Submitted to: PLoS One
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/18/2013
Publication Date: 2/22/2013
Citation: Salazar, J., Deng, K., Tortorello, M., Brandl, M., Wang, H., Zhang, W. 2013. Genes ycfR, sirA and yigG contribute to the surface attachment of Salmonella enterica Typhimurium and Saintpaul to fresh produce. PLoS One. 8(2):e57272. doi:10.1371/journal.pone0057272. Interpretive Summary: Fresh vegetables have been recurrently associated with salmonellosis outbreaks. Minimally processed vegetables undergo a chlorine-based wash to prevent cross-contamination in the flume water in the processing plant. We investigated the role of three Salmonella genes that are upregulated during sublethal chlorine stress in the interaction of the pathogen with spinach leaves and grape tomatoes. Mutants with deletions of ycfR, sirA, and yigG were compromised in biofilm formation in vitro, suggesting that the genes are involved in attachment of Salmonella to surfaces. Deletions of ycfR, sirA, and yigG reduced also attachment of both Salmonella Typhimurium and Saintpaul to fresh produce with or without chlorine stress. Our findings suggest that ycfR, sirA, and yigG may collectively contribute to S. enterica attachment to produce during industrial minimal processing.
Technical Abstract: Salmonella enterica is frequently implicated in human foodborne disease outbreaks associated with minimally-processed produce. However, the molecular mechanisms underlying the association of this enteric pathogen with fresh produce remain largely unexplored.In previous studies, we determined that the expression of a putative stress regulatory gene ycfR was most significantly induced in S. enterica upon its exposure to sublethal chlorine stress, indicating a potential role of this gene in enabling bacterial survival during the minimal processing of produce. Two other genes including sirA, which is involved in biofilm formation and yigG, a gene of unknown function were also differentially regulated under chlorine stress. Here we constructed in-frame deletions of ycfR, sirA, and yigG in two different S. enterica serotypes that have been associated with previous outbreaks linked to fresh produce: S. Typhimurium and S. Saintpaul. Bacterial biofilm productivity, cell aggregation and hydrophobicity, chlorine resistance, and attachment to intact spinach leaf and grape tomato surfaces were evaluated among wild-type strains, deletion mutants, and their respective complementation mutants. S. Typhimurium 'ycfR showed significantly reduced chlorine resistance. 'ycfR, 'sirA, and 'yigG mutants displayed reduced biofilm production in both serovars; the greatest reduction was observed in S. Saintpaul 'sirA. S. Typhimurium 'ycfR and S. SaintPaul 'yigG both showed significant increase in cell aggregation. However, no change was observed in cell hydrophobicity in any of the mutants. Deletions of ycfR, sirA, and yigG reduced attachment of both serovars to fresh produce with or without chlorine stress. Attachment of S. Typhimurium 'ycfR to the plant surfaces under chlorine stress was undetectable. Our findings suggest that ycfR, sirA, and yigG may collectively contribute to S. enterica attachment to produce during industrial minimal processing.