Severely Heat Injured Survivors of E. coli O157:H7 ATCC 43888 Display Variable and Heterogeneous Stress Resistance Behavior.

Elisa Gayán,Sander K Govers,Abram Aertsen,Chris W Michiels

doi:10.3389/fmicb.2016.01845

Abstract

Although minimal food processing strategies aim to eliminate foodborne pathogens and spoilage microorganisms through a combination of mild preservation techniques, little is actually known on the resistance behavior of the small fraction of microorganisms surviving an inimical treatment. In this study, the conduct of severely heat stressed survivors of E. coli O157:H7 ATCC 43888, as an indicator for the low infectious dose foodborne enterohemorrhagic strains, was examined throughout their resuscitation and outgrowth. Despite the fact that these survivors were initially sublethally injured, they were only marginally more sensitive to a subsequent heat treatment and actually much more resistant to a subsequent high hydrostatic pressure (HHP) shock in comparison with unstressed control cells. Throughout further resuscitation, however, their initial HHP resistance rapidly faded out, while their heat resistance increased and surpassed the initial heat resistance of unstressed control cells. Results also indicated that the population eventually emerging from the severely heat stressed survivors heterogeneously consisted of both growing and non-growing cells. Together, these observations provide deeper insights into the particular behavior and heterogeneity of stressed foodborne pathogens in the context of food preservation.

Highlights

Consumer demand for fresh-like foods challenges the food industry to design minimal processing strategies that improve the retention of the nutritional and sensorial properties of the food while ensuring its microbial safety and stability
Stationary phase cultures were obtained by inoculating test tubes containing 4 ml of Tryptone Soy Broth (TSB; Oxoid, Basingstoke, UK) with a single colony grown on a Tryptone Soy Agar (TSA) plate, and incubated aerobically with shaking (300 rpm) for 18 h at 37◦C
Heat stressed populations were generated by exposing a stationary phase population of E. coli ATCC 43888 to 56◦C for 15 min, thereby causing a ca. 3.2 log10 cycle reduction in viability

Summary

Introduction

Consumer demand for fresh-like foods challenges the food industry to design minimal processing strategies that improve the retention of the nutritional and sensorial properties of the food while ensuring its microbial safety and stability. Some natural antimicrobial compounds (e.g., essential oils, reuterin, nisin) or enzymes (e.g., lysozyme, lactoperoxidase) have been shown to act synergistically with mild heat, PEF, or HHP in inactivating pathogens, thereby allowing a reduction in the intensity of the physical treatment and the concentration of antimicrobials and consequent impact on food quality (Masschalck et al, 2001; Saldaña et al, 2012; Ait-Ouazzou et al, 2013; Feyaerts et al, 2015; Montiel et al, 2015) While these examples underscore the potential of hurdle technology, a successful combination of hurdles is often made serendipitously, with little or no insights in the mechanisms underlying the possible synergy or antagonism between different hurdles in terms of microbial inactivation (i.e., when the lethal effect of the combined treatment is higher or lower, respectively, than the sum of the effect of each individual hurdle). Little is known about the physiological response and subsequent behavior that is triggered in the small fraction of cells that manage to survive one or more mild hurdles, often because of the technical difficulties in properly studying the features or dynamics occurring within a minute subpopulation

Methods

Results

Conclusion