Abstract
Listeria monocytogenes is a food-borne pathogen of significant threat to public health. High Hydrostatic Pressure (HHP) treatment can be used to control L. monocytogenes in food. The CtsR (class three stress gene repressor) protein negatively regulates the expression of class III heat shock genes. In a previous study, a spontaneous ctsR L. monocytogenes deletion mutant 2-1 that was able to survive under HHP treatment was identified; however, there is only limited information about the mechanisms of survival and adaptation of this mutant in response to high pressure. Microarray technology was used to monitor the gene expression profiles of ctsR mutant 2-1 under pressure treatments (450 Mpa, 3min). Some of the gene expression changes determined by microarray assays were confirmed by real-time RT-PCR analyses. Compared to non-pressure-treated ctsR mutant 2-1, 14 genes were induced (> 2-fold increase) in the ctsR deletion mutant whereas 219 genes were inhibited (< -2-fold decrease) by pressure treatments. The induced genes included genes encoding proteins involved in synthesis of purines, pyrimidines, nucleosides, and nucleotides, transport and binding, transcription, cell membrane, DNA and energy metabolism, protein synthesis, and unknown functions. The inhibited genes included genes encoding proteins for transport and binding, cell envelope, transcription, amino acid biosynthesis, regulatory functions, cellular processes and central intermediary metabolism. The information concerning L. monocytogenes survival under HHP at the molecular level may contribute to improved HHP treatments for food processing.
Highlights
L. monocytogenes is a Gram-positive bacterium that can cause listeriosis in animal and human populations
Because L. monocytogenes is widely distributed in the environment and survive under very harsh conditions, it is very difficult to eliminate this pathogen from foods and/or food processing plants
The L. monocytogenes Scott A ctsR mutant 2-1 and L. monocytogenes strain ScottA obtained from Dr Joerger at University of Delaware were treated with high pressure (450 Mpa, 3 min) as described previously [12]
Summary
L. monocytogenes is a Gram-positive bacterium that can cause listeriosis in animal and human populations. Outbreaks of listeriosis have been associated with the consumption of contaminated food products including ready-to-eat (RTE) meats and dairy products [1,2]. High Hydrostatic processing (HHP) is a process that can inactivate microorganisms without significant deterioration of food quality. HHP has been used as a non-thermal preservation technique for processing of meats and dairy products to control L. monocytogenes and extend product shelf-life. Pressures within the range of 300 to 600 MPa are used to inactivate vegetative cells of microorganisms, including pathogens such as L. monocytogenes. The efficiency of HHP depends on the pressure, time, and composition of the food [3]. The inactivation of L. monocytogenes by HHP (600 MPa, 5min) ranged from 1.82 to 3.85 Log units, depending on the type of dry-cured ham [4]
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