Purpose: This study investigates whether stressing Salmonella via long-term storage and inoculating on oregano results in detectable gene expression changes and if observed changes suggest potential adaptive processes that enable pathogen survival on spices.
Methods: Salmonella enterica serotype Montevideo was inoculated in 250mL of TSB, incubated 16-24 hr at 37oC, and subsequently transferred to 4oC for long-term storage. Monthly, 500 ul of the inoculum stored at 4oC was spiked onto 25g oregano with 250 mL TSB plus 2% v/v corn oil, and incubated 16-24 hr at 37oC with shaking. Total RNA was extracted, enriched for mRNA, sequencing library generated and sequenced on the Illumina Miseq platform. GenBank CDS annotations were processed in CLC Bio Workbench.
Results: Of 4367 loci, 61% displaying discernable number of sequence reads were taken for further analysis. Differential transcription was observed over time. Genes involved in a broad spectrum of processes from housekeeping to stress response were observed. They include chaperone, cold shock, SOS-response, DNA replication and repair proteins, proteases, methylase, and those involved in ammonia reduction and alternative metabolic pathways.
Significance: Transcriptomics is a powerful tool for capturing snapshots of molecular changes in gene expression over time. These molecular changes most likely reflect adaptive physiological changes that enhance the survival of Salmonella in highly stressful environments, like low-moisture foods such as spices. This information can be used to advance the FDA’s mitigation, detection, and eradication of foodborne pathogens in the food supply.