29G-28 |
Variation in biofilm formation by Listeria monocytogenes strains at 4°C and 22°C |
L. A. KESKINEN1, E. C. D. Todd2, and E. T. Ryser1. (1) Dept. of Food Science & Human Nutrition, Michigan State Univ., 2100 S. Anthony Hall, East Lansing, MI 48824-1225, (2) National Food Safety & Toxicology Center, Michigan State Univ., 165 Food Safety & Toxicology Bldg., East Lansing, MI 48824-1302 Potential biofilm formation by L. monocytogenes on food contact surfaces can lead to cross-contamination and further spread of Listeria in commercial and home settings. Additional research on Listeria biofilm formation is needed to help better define the impact of food preparation practices on listeriosis estimations being developed in current risk assessments. This study characterized the biofilm-forming capabilities of a diverse set of 129 L. monocytogenes strains at 4 and 22°C. A total of 129 L. monocytogenes isolates from food, environmental, veterinary and clinical sources comprised of 16 different ribotypes were assessed for biofilm formation in Modified Welshimer’s Broth (inoculated to contain 102 cfu/ml) using 96-well untreated polystyrene microtiter plates (3 wells/strain x 3 replicates). Following 4 and 60 days of incubation at 22 and 4°C, respectively, the microtiter plate wells were emptied, rinsed and air-dried. After staining fixed cells with crystal violet, the optical density (OD) of the resolubilized dye was read at 570 nm. At 22°C, 69% and 97% of the OD’s were within one and two standard deviations of the mean -- 0.624 + 0.418 and 0.836, respectively. At 4°C, 70% and 97% of the OD’s were within one and two standard deviations of the mean -- 0.094 + 0.053 and 0.106, respectively, with 58 of 129 (45%) 129 strains failing to produce detectable biofilms at 4°C. Significant differences in biofilm formation were observed between strains of the same ribotype. While most L. monocytogenes strains formed biofilms at room temperature, appreciable biofilm formation was typically absent at 4°C, thus suggesting the inability of most L. monocytogenes strains to produce significant biofilms in otherwise clean cold storage areas. Recognizing that only 3% of our isolates were particularly strong biofilm formers should be useful in refining current risk assessments.
Session 29G, Food Microbiology: General
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