Transcription of Escherichia Coli O157:H7 Key Virulence Genes During Growth in Liquid Medium and Rocket (Eruca Sativa) at 4 and 10oC

Abstract

The aim of the present study was to comparatively assess the transcription of key virulence genes, during growth of an Escherichia coli O157:H7 isolate in liquid medium and rocket (Eruca sativa) at different temperatures and time. For that purpose, rocket leaves and BHI broth were inoculated with 7.5 log CFU/g or CFU/mL, respectively, and incubated at 4 and 10oC. Sampling took place upon inoculation and after 0.5, 6 and 24 h of incubation; the RNA was stabilized and the transcription of stx1, stx2, eae, ehxA and etpD was assessed by RT-qPCR. Downregulation of stx1 and ehxA during growth on rocket surface at 4oC, upregulation of stx2 and eae during growth on rocket surface at both 4 and 10oC and the upregulation of etpD and ehxA during growth on rocket surface at 4 and 10oC, respectively, were observed. In addition, increase of incubation temperature, i.e. from 4 to 10oC resulted in upregulation of stx1 and downregulation of stx2 and eae. These results suggest that through differential regulation of genes encoding for virulence factors, the virulence potential of E. coli O157:H7 may be altered when it resides on the surface of rocket, at least for short time and at temperature relevant to its storage. However, further research is still necessary in order to improve our understanding of the physiology of this foodborne pathogen and the responses during exposure to food-related stresses.