Abstract
Salmonella spp., one of the most common foodborne bacterial pathogens, has the ability to survive under desiccation conditions in foods and food processing facilities for years. This raises the concerns of Salmonella infection in humans associated with low water activity foods. Salmonella responds to desiccation stress via complex pathways involving immediate physiological actions as well as coordinated genetic responses. However, the exact mechanisms of Salmonella to resist desiccation stress remain to be fully elucidated. In this study, we screened a genome-saturating transposon (Tn5) library of Salmonella Typhimurium (S. Typhimurium) 14028s under the in vitro desiccation stress using transposon sequencing (Tn-seq). We identified 61 genes and 6 intergenic regions required to overcome desiccation stress. Salmonella desiccation resistance genes were mostly related to energy production and conversion; cell wall/membrane/envelope biogenesis; inorganic ion transport and metabolism; regulation of biological process; DNA metabolic process; ABC transporters; and two component system. More than 20% of the Salmonella desiccation resistance genes encode either putative or hypothetical proteins. Phenotypic evaluation of 12 single gene knockout mutants showed 3 mutants (atpH, atpG, and corA) had significantly (p < 0.02) reduced survival as compared to the wild type during desiccation survival. Thus, our study provided new insights into the molecular mechanisms utilized by Salmonella for survival against desiccation stress. The findings might be further exploited to develop effective control strategies against Salmonella contamination in low water activity foods and food processing facilities.
Highlights
Salmonella is one of the most common causes of foodborne illness worldwide
DNA was extracted from IP and OP and the transposon sequencing (Tn-seq) amplicon libraries were prepared for HiSeq Illumina sequencing as described in Material and Methods
Illumina sequencing reads were demultiplexed based on a perfect match to sample barcodes and Tn5-junction sequences (20 bp) were extracted allowing some mismatches to the mosaic end of Tn5
Summary
Salmonella is one of the most common causes of foodborne illness worldwide. It can withstand a spectrum of hostile milieus such as, desiccation found in natural and food industry settings (Spector and Kenyon, 2012). Salmonella Genes for Desiccation Survival outbreak illness and 63 deaths due to consumption of contaminated low-aw foods and spices during the period from 2007 to 2012. Typhimurium genes differentially expressed in response to different humectants, agents that reduce water content of food products, do not reflect low low-aw but rather are linked to specific humectants (Finn et al, 2015). The expression-based analysis does not provide insight into genes that are constitutively expressed or gene for which expression of the encoding proteins is controlled by post-transcriptional modifications These limitations of expression-based analysis can be largely overcome by a more direct functional screening approach such as, transposon sequencing (Tn-seq) of saturated mutant libraries employed in this study.
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