Purpose: The purpose of this study was to define and compare transcriptomes of PUL R1-0006 and SL476, exposed to heat shock mimicking scald temperatures, to investigate which genes may be contributing to survival and enhanced virulence of Salmonella Heidelberg.
Methods: RNA from each strain was extracted, in triplicate, from control (37°C) and heat shocked (7.5 min at 56°C) stationary-phase cultures using standard Trizol and rRNA-depletion methods. RNA quality and DNA and rRNA depletion were assessed. Libraries were constructed using the Illumina Scriptseq v2 library kit and sequenced on an Illumina HiSeq. Reads were trimmed and aligned; counts were obtained using HTSeq (v.0.6.1). Differential expression was determined using DESeq2 (v.1.12.4) in R (v3.3.1). Genes with log2-fold change >1 and adj. P<0.01 were considered significantly, differentially expressed (DE).
Results : In PUL R1-006, known heat shock-associated genes dnaJ and rpoH were upregulated, while groS was downregulated. Interestingly, a different subset of heat shock-associated genes rpoH and hscAB were upregulated and ibpA was downregulated in SL476. Twenty-four and 37 virulence-associates genes were DE in PUL R1-0006 and SL476, respectively, including genes in Salmonella pathogenicity islands (SPI-1 and SPI-2). Sixteen antibiotic resistance genes or efflux pumps were DE in PUL R1-0006; 15 were identified in SL476.
Significance: This is the first study to capture the transcriptome of Salmonella Heidelberg. Preliminary analyses suggested that exposure of Salmonella Heidelberg to heat shock conditions relevant to poultry processing may result in increased virulence and tolerance to antibiotics, which could partially explain the severity of disease associated with this serovar. Further studies are necessary to explore this relationship.