Ethanol adaptation induces direct protection and cross-protection against freezing stress inSalmonella entericaserovar Enteritidis

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Abstract

Aims:

Salmonella enterica serovar Enteritidis (Salm. Enteritidis) encounters mild ethanol stress during its life cycle. However, adaptation to a stressful condition may affect bacterial resistance to subsequent stresses. Hence, this work was undertaken to investigate the influences of ethanol adaptation on stress tolerance of Salm. Enteritidis.

Methods and Results:

Salmonella Enteritidis was subjected to different ethanol adaptation treatments (2·5–10% ethanol for 1 h). Cellular morphology and tolerance to subsequent environmental stresses (15% ethanol, −20°C, 4°C, 50°C and 10% NaCl) were evaluated. It was found that 10% was the maximum ethanol concentration that allowed growth of the target bacteria. Ethanol adaptation did not cause cell-surface damage in Salm. Enteritidis as revealed by membrane permeability measurements and electron micrograph analysis. Salmonella Enteritidis adapted with 2·5–10% ethanol displayed an enhanced resistance to a 15%-ethanol challenge compared with an unchallenged control. The maximum ethanol resistance was observed when ethanol concentration used for ethanol adaptation was increased to 5·0%. Additionally, pre-adaptation to 5·0% ethanol cross-protected Salm. Enteritidis against −20°C, but not against 4°C, 50°C or 10% NaCl.

Conclusions:

Ethanol adaptation provided Salm. Enteritidis direct protection from a high level ethanol challenge and cross-protection from freezing, but not other stresses tested (low temperature, high salinity or high temperature).

Significance and Impact of the Study:

The results are valuable in developing adequate and efficient control measures for Salm. Enteritidis in foods.

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