Abstract
High hydrostatic pressure (HHP) processing is an attractive non-thermal alternative to food pasteurization. Nevertheless, the large inter- and intra-species variations in HHP resistance among foodborne pathogens and the ease by which they can acquire extreme resistance are an issue of increasing concern. Since RpoS activity has been considered as a central determinant in the HHP resistance of E. coli and its pathovars, this study probed for the potential of an E. coli MG1655 ΔrpoS mutant to acquire HHP resistance by directed evolution. Despite the higher initial HHP sensitivity of the ΔrpoS mutant compared to the wild-type strain, evolved lineages of the former readily managed to restore or even succeed wild-type levels of resistance. A number of these ΔrpoS derivatives were affected in cAMP/CRP regulation, and this could be causally related to their HHP resistance. Subsequent inspection revealed that some of previously isolated HHP-resistant mutants derived from the wild-type strain also incurred a causal decrease in cAMP/CRP regulation. cAMP/CRP attenuated HHP-resistant mutants also exhibited higher resistance to fosfomycin, a preferred treatment for STEC infections. As such, this study reveals attenuation of cAMP/CRP regulation as a relevant and RpoS-independent evolutionary route towards HHP resistance in E. coli that coincides with fosfomycin resistance.
Highlights
High hydrostatic pressure (HHP) treatment is a promising alternative to conventional thermal pasteurization of foods as it is able to improve the microbial stability and safety of foods without compromising its fresh-like attributes
O157:H7 had revealed that disruption of cyclic adenosine monophosphate (cAMP)/CRP homeostasis could confer HHP resistance[18], we examined whether cAMP/CRP regulation was compromised in the evolved ΔrpoS mutants
RpoS activity has previously been established as a central determinant in stationary phase HHP resistance in E. coli, and mutations upregulating the activity of this sigma factor highlight one evolutionary strategy towards HHP resistance development[11, 15]
Summary
High hydrostatic pressure (HHP) treatment is a promising alternative to conventional thermal pasteurization of foods as it is able to improve the microbial stability and safety of foods without compromising its fresh-like attributes. The mechanism underlying bacterial inactivation by HHP treatment is still not well understood; some cellular targets and stress responses involved in pressure survival have been identified[7,8,9]. The large variability in pressure resistance among natural STEC isolates has been related to polymorphisms in their rpoS allele and the corresponding variations in cellular RpoS activity[5, 11]. These polymorphisms are thought to reflect the evolutionary adaptation of different E. coli populations to their particular ecological niches[12, 13]. An asterisk indicates statistically significant differences (P ≤ 0.05) between the inactivation of the parental ∆rpoS and WT strain at indicated pressures
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