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Aims:  To examine the role of the alternative general stress sigma factor σB on the resistance of Staphylococcus aureus to stresses of relevance to food preservation, with special emphasis on emerging technologies such as pulsed electric fields (PEF) and high hydrostatic pressure (HHP). Methods and Results:  S. aureus strain Newman and its isogenic ΔsigB mutant were grown to exponential and stationary growth phases and its resistance to various stresses was tested. The absence of the σB factor caused a decrease in the resistance to heat, PEF, HHP, alkali, acid and hydrogen peroxide. In the case of heat, the influence of the σB factor was particularly important, and decreases in decimal reduction time values of ninefold were observed as a result of its deficiency. The increased thermotolerance of the parental strain as compared with the sigB mutant could be attributed to a better capacity to sustain and repair sublethal damages caused by heat. Conclusions:  σB factor provides S. aureus cells with resistance to multiple stresses, increasing survival to heat, PEF and HHP treatments. Significance and Impact of the Study:  Results obtained in this work help in understanding the physiological mechanisms behind cell survival and death in food‐processing environments.

Aims: To study the influence of growth temperature on the resistance of Escherichia coli to three agents of different nature: heat, pulsed electric field (PEF) and hydrogen peroxide. Methods and Results: Escherichia coli cells were grown to stationary phase at 10°C, 20°C, 30°C, 37°C and 42°C. Survival curves to a heat treatment at 57AE5°C, to a PEF treatment at 22 kV cm )1 and to 40 mmol l )1 hydrogen peroxide were obtained and fitted to a model based on the Weibull distribution to describe and compare the inactivation. Time to inactivate the first log cycle of the population at 57AE5°C of cells grown at 42°C was sixfold higher than that corresponding to cells grown at 10°C. On the contrary, cells grown at 10°C and 20°C were more resistant to PEF and hydrogen peroxide treatments. Conclusions:The influence of growth temperature on bacterial resistance depends on the stress applied. Cells grown at higher temperatures were more heat resistant, but more sensitive to PEF and hydrogen peroxide. Significance and Impact of the Study: Results obtained in this investigation help in understanding the physiology of bacterial resistance and the inactivation mechanisms of different technologies.

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