The foodborne pathogen Listeria monocytogenes has the ability to survive and grow under a wide range of adverse conditions encountered both in food, processing environment and during the host passage. Listeriosis outbreaks are often associated with the ingestion of contaminated dairy products, mainly soft cheese. During cheese manufacturing this pathogen can experience sublethal stresses such as low pH and high salt content, which may induce tolerance responses and potentially increase its survival during gastrointestinal passage. The present study aimed to: a) evaluate how two dairy isolates mount their tolerance responses to a sublethal pH and salt content in a defined medium; b) investigate the impact of low pH and salt adaptation in a cheese-simulated medium on the survival of cheese and dairy isolates during gastric stress and ultimately c) determine the influence of low pH and salt adaptation in a cheese-based medium on the survival of cheese and dairy isolates during gastrointestinal stress. The intracellular proteomes of adapted (pH 5.5 and 3.5% (w/v) NaCl) and non-adapted cultures (pH 7.0, no NaCl added) were evaluated via 2-DE gel electrophoresis. In the defined medium acid and salt tolerance were different. All strains were able to successfully survive the gastric and the gastrointestinal challenge and both adapted and non-adapted cells were equally able (P>0.05) to overcome the gastric and the gastrointestinal stress. However, the proteome profiles revealed a significant intra-strain variation, both in defined medium and when challenge with the gastric and gastrointestinal fluids. In each protein functional group a distinct set of proteins was observed. Also adapted and non-adapted cells beat the gastrointestinal stress with a different proteome. This study provides information that may contribute to a better understanding of the molecular mechanisms underlying tolerance responses of L. monocytogenes in acidic foods and their effect on coping the gastrointestinal stress.Universidade do Algarve, Departamento de Ciências Biomédicas e Medicin
