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Construction of Listeria monocytogenes mutants with in-frame deletions in the Phosphotransferase Transport System (PTS) and analysis of their growth under stress conditions

Yanhong Liu, Marina Ceruso, Yuji Jiang, Atin R. Datta, Laurenda Carter, Errol Strain, Tiziana Pepe, Aniello Anastasi, Pina Fratamico
Journal of food science 2013 v.78 no.9 pp. 1392-1398
Listeria monocytogenes, carbon, food pathogens, foods, genes, mutants, nisin, pH, sodium chloride, stress response, sugars
Listeria monocytogenes is a food-borne pathogen that is difficult to eliminate due to its ability to survive under different stress conditions such as low pH and high salt. To better control this pathogen in food, it is important to understand its survival mechanisms under these stress conditions. LMOf2365_0442, 0443, 0444 encode for PTS permease (fructose-specific IIABC components) that is responsible for sugar transport. LMOf2365_0445 encodes for glycosyl hydrolase. These genes were induced by high pressure and inhibited under salt treatments; therefore, we hypothesized that genes encoding these PTS proteins may be involved in general stress responses. To study the function of these genes, deletion mutants of the PTS genes (LMOf2365_0442, LMOf2365_0443, LMOf2365_0444) and the downstream gene LMOf2365_0445 were created in L. monocytogenes strain F2365. These deletion mutants were tested under different stress conditions. The growth of 'LMOf2365_0445 was increased under nisin (125 µg/ml) treatments compared to the wild type (p<0.01). The growth of 'LMOf2365_0442 in salt (brain heart infusion medium with 5% NaCl) was significantly increased (p< 0.01), and 'LMOf2365_0442 showed increased growth under acidic conditions (pH 5.0) compared to the wild type (p<0.01). The results from phenotypic arrays demonstrated that some of these mutants showed slightly slower growth under different carbon sources and basic conditions. The results indicate that deletion mutants 'LMOf2365_0442 and 'LMOf2365_0445 were more resistant to multiple stress conditions compared to the wild type, suggesting that they may contribute to the general stress response in L. monocytogenes. An understanding of the growth of these mutants under multiple stress conditions may assist in the development of intervention strategies to control L. monocytogenes in food.