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 (fo 70 10) 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°=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°=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°=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. © 2013, American Society for Microbiology.