title: Effect of osmotic stress and culture density on invasiveness of Listeria monocytogenes strains.
abstract: The effect of osmotic stress on its capacity to invade the human enterocytic cell line HT-29 was studied in the early log through the stationary phase in 10 L. monocytogenes strains representing three genetically independent lineages. The results demonstrate that the transition of the bacteria from the log to the stationary phase results in a stepwise reduction of invasiveness. This effect was heterogeneous in the studied L. monocytogenes population, as the range of invasiveness reduction between the log and stationary phases varied from 10- to 380-fold depending on the strain. Ten-minute exposure to 0.3 M NaCl was sufficient to generate invasiveness alteration. No significant change in invasiveness induction caused by osmotic stress was found between the different points of the log phase (OD₆₀₀ 0.4-1.2), being significantly different in the early log phase (OD₆₀₀ 0.2-0.3) and in the stationary phase after 18 h of culture. The level of internalins and opuCA transcripts in response to osmotic stress did not correlate with invasiveness alteration in most L. monocytogenes strains. Prolongation of stress exposure to 1 h and an increase in NaCl concentration from 0.3 to 1.8 M had no significant effect on a further increase in invasiveness. Short exposure times and low NaCl concentrations were sufficient for the generation of maximal invasiveness response of L. monocytogenes. It appears that although stationary-phase bacteria exhibit lower invasiveness than log-phase bacteria, they have a greater capacity to enhance their pathogenicity in response to stress.
authors.affiliation: Department of Food Hygiene and Consumer Health Protection, Wrocław University of Environmental and Life Sciences, Wrocław, Poland.
authors.forename: Ewa
authors.initials: E
authors.lastname: Wałecka
authors.forename: Jerzy
authors.initials: J
authors.lastname: Molenda
authors.forename: Renata
authors.initials: R
authors.lastname: Karpíšková
authors.forename: Jacek
authors.initials: J
authors.lastname: Bania
mesh_terms: D001426:Bacterial Proteins / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial / Q000187:drug effects; D019073:HT29 Cells; D006801:Humans; D008089:Listeria monocytogenes / Q000187:drug effects / Q000254:growth & development / Q000472:pathogenicity / Q000502:physiology*; D012965:Sodium Chloride / Q000494:pharmacology; D013312:Stress, Physiological; D013997:Time Factors
chemical_list: D001426:Bacterial Proteins; D012965:Sodium Chloride