title: Whole-genome transcriptional analysis of Escherichia coli during heat inactivation processes related to industrial cooking.
abstract: Escherichia coli K-12 was grown to the stationary phase, for maximum physiological resistance, in brain heart infusion (BHI) broth at 37°C. Cells were then heated at 58°C or 60°C to reach a process lethality value \[\mathbf{\left(}{{\mathit{F}}^{\mathit{o}}}_{\mathbf{70}}^{\mathbf{10}}\mathbf{\right)} \] of 2 or 3 or to a core temperature of 71°C (control industrial cooking temperature). Growth recovery and cell membrane integrity were evaluated immediately after heating, and a global transcription analysis was performed using gene expression microarrays. Only cells heated at 58°C with F(o) = 2 were still able to grow on liquid or solid BHI broth after heat treatment. However, their transcriptome did not differ from that of bacteria heated at 58°C with F(o) = 3 (P value for the false discovery rate [P-FDR] > 0.01), where no growth recovery was observed posttreatment. Genome-wide transcriptomic data obtained at 71°C were distinct from those of the other treatments without growth recovery. Quantification of heat shock gene expression by real-time PCR revealed that dnaK and groEL mRNA levels decreased significantly above 60°C to reach levels similar to those of control cells at 37°C (P < 0.0001). Furthermore, despite similar levels of cell inactivation measured by growth on BHI media after heating, 132 and 8 genes were differentially expressed at 71°C compared to 58°C and 60°C at F(o) = 3, respectively (P-FDR < 0.01). Among them, genes such as aroA, citE, glyS, oppB, and asd, whose expression was upregulated at 71°C, may be worth investigating as good biomarkers for accurately determining the efficiency of heat treatments, especially when cells are too injured to be enumerated using growth media.
authors.affiliation: Department of Animal Science, Faculty of Agriculture and Food Sciences, Université Laval, Quebec City, Québec, Canada.
authors.forename: A
authors.initials: A
authors.lastname: Guernec
authors.forename: P
authors.initials: P
authors.lastname: Robichaud-Rincon
authors.forename: L
authors.initials: L
authors.lastname: Saucier
mesh_terms: D003296:Cooking; D048168:Escherichia coli K12 / Q000235:genetics* / Q000254:growth & development* / Q000502:physiology; D020869:Gene Expression Profiling; D005819:Genetic Markers; D016680:Genome, Bacterial; D055106:Genome-Wide Association Study; D018869:Heat-Shock Response; D008460:Meat / Q000382:microbiology*; D050296:Microbial Viability; D060888:Real-Time Polymerase Chain Reaction
chemical_list: D005819:Genetic Markers