Abstract
BackgroundInformation regarding the Alkali-Tolerance Response (AlTR) in Listeria monocytogenes is very limited. Treatment of alkali-adapted cells with the protein synthesis inhibitor chloramphenicol has revealed that the AlTR is at least partially protein-dependent. In order to gain a more comprehensive perspective on the physiology and regulation of the AlTR, we compared differential gene expression and protein content of cells adapted at pH 9.5 and un-adapted cells (pH 7.0) using complementary DNA (cDNA) microarray and two-dimensional (2D) gel electrophoresis, (combined with mass spectrometry) respectively.ResultsIn this study, L. monocytogenes was shown to exhibit a significant AlTR following a 1-h exposure to mild alkali (pH 9.5), which is capable of protecting cells from subsequent lethal alkali stress (pH 12.0). Adaptive intracellular gene expression involved genes that are associated with virulence, the general stress response, cell division, and changes in cell wall structure and included many genes with unknown functions. The observed variability between results of cDNA arrays and 2D gel electrophoresis may be accounted for by posttranslational modifications. Interestingly, several alkali induced genes/proteins can provide a cross protective overlap to other types of stresses.ConclusionAlkali pH provides therefore L. monocytogenes with nonspecific multiple-stress resistance that may be vital for survival in the human gastrointestinal tract as well as within food processing systems where alkali conditions prevail. This study showed strong evidence that the AlTR in L. monocytogenes functions as to minimize excess alkalisation and energy expenditures while mobilizing available carbon sources.
Highlights
Information regarding the Alkali-Tolerance Response (AlTR) in Listeria monocytogenes is very limited
Protein synthesis inhibition Preliminary experiments have shown that L. monocytogenes 10403S grows in a wide range of pH values (5.0 to 9.0)
Chloramphenicol was used to determine whether de novo protein synthesis is required for the induction of AlTR
Summary
Information regarding the Alkali-Tolerance Response (AlTR) in Listeria monocytogenes is very limited. The resistance of L. monocytogenes to alkali stress is of particular concern especially when mild alkali treatments are used in the food industry [1,2,3,4,5,6] and it may account for the bacterium's persistence in such environments [1]. Listeria's ability to tolerate high pH conditions, suggest that this organism is capable of resisting pHrelated human defence mechanisms, e.g. a rise and fall of (page number not for citation purposes). The ability of Listeria to induce an Alkali-Tolerance Response (AlTR) could be a significant factor in predicting the pathogen's fate in alkali foods/food processing systems and the pathogen's virulence within the human gastrointestinal system
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