title: Sodium chloride enhances adherence and aggregation and strain variation influences invasiveness of Listeria monocytogenes strains.
abstract: Some subtypes of Listeria monocytogenes can persist in the food-processing industry, but the reasons for such persistence are not known. In the present study, 10 strains of L. monocytogenes representing known persistent randomly amplified polymorphic DNA (RAPD) types from fish processing plants were compared to eight strains of different RAPD type and origin (clinical, food, and animal). All 18 strains of L. monocytogenes had similar growth patterns at different temperatures (5 or 37 degrees C) or different salinities (0.5 or 5% NaCl), and all strains formed a thin layer of adhered cells on a plastic surface when cultured in tryptone soya broth (TSB) with a total of 1% glucose. Many ready-to-eat foods, such as cold-smoked fish, contain NaCl at concentrations of 2 to 5%, and NaCl is present in the processing environment. Adding NaCl to TSB changed the adhesion patterns of all strains, and all adhered better when NaCl was added. Also, the addition of NaCl caused a marked aggregation of 13 of the strains; however, 5 of the 18 strains did not aggregate in the presence of up to 5% NaCl. The aggregates stuck to the plastic surface, and this occurred in all but one of the persistent RAPD types. Four strains represented one particular RAPD type that has been isolated as a persistent RAPD type in several fish processing plants for up to 10 years. Because this RAPD type often can contaminate fish products, it is important to address its potential virulence. The 18 strains differed markedly in their ability to invade Caco-2 cells, and the four strains representing the universal persistent RAPD type were the least invasive (10(2) to 10(3) CFU/ml), whereas other strains invaded Caco-2 cells at levels of 10(4) to 10(5) CFU/ml. Five of the 18 strains belonged to the genetic lineage 1 and were the most invasive. Although the most commonly isolated persistent RAPD type was low invasive, it is important to understand why moderate salinity facilitates aggregation and biofilm formation, for this understanding can be beneficial in developing procedures to reduce processing plant contamination.
authors: Danish Institute for Fisheries Research, Department of Seafood Research, Søltofts Plads, DTU bldg. 221, DK-2800 Kgs. Lyngby, Denmark. aje@difres.dk
authors: Anne
authors: A
authors: Jensen
authors: Marianne H
authors: MH
authors: Larsen
authors: Hanne
authors: H
authors: Ingmer
authors: Birte Fonnesbech
authors: BF
authors: Vogel
authors: Lone
authors: L
authors: Gram
mesh_terms: D000818:Animals; D001422:Bacterial Adhesion / Q000187:drug effects*; D018938:Caco-2 Cells / Q000382:microbiology; D015169:Colony Count, Microbial; D004269:DNA, Bacterial / Q000302:isolation & purification; D004305:Dose-Response Relationship, Drug; D005506:Food Contamination / Q000032:analysis; D005516:Food Microbiology; D014644:Genetic Variation; D006801:Humans; D008089:Listeria monocytogenes / Q000187:drug effects / Q000235:genetics / Q000472:pathogenicity / Q000502:physiology; D019105:Random Amplified Polymorphic DNA Technique; D018570:Risk Assessment; D012965:Sodium Chloride / Q000494:pharmacology*; D013696:Temperature; D014774:Virulence
chemical_list: D004269:DNA, Bacterial; D012965:Sodium Chloride