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Title: Synergistic effects of sodium chloride, Glucose, and temperature on biofilm formation by Listeria monocytogenes serotype 1/2a and 4b strains

item PAN, YOUWEN - North Carolina State University
item Breidt, Frederick
item Gorski, Lisa

Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/23/2009
Publication Date: 3/1/2010
Citation: Pan Y, Breidt F, Gorski LA. 2010. Synergistic effects of sodium chloride, Glucose, and temperature on biofilm formation by Listeria monocytogenes serotype 1/2a and 4b strains. Appl Environ Microbiol. 76(5):1433-1441.

Interpretive Summary: Some disease causing bacteria can form films on food processing equipment. One particularly dangerous bacterial species of this type is Listeria monocytogenes, which can cause a fatal disease in humans. The films these bacteria form in food processing equipment can protect the cells from cleaning and sanitizing treatments, and the bacteria can get into the processed foods. We investigated the environmental conditions that allow these films of bacteria to form, and found that certain combinations of temperature, salt, nutrients can encourage film formation. We also studied how film thickness is related to cell growth. The knowledge gained about how biological films of bacteria develop may be helpful in preventing the formation of these films.

Technical Abstract: Biofilm formation by Listeria monocytogenes is generally associated with its persistence in the food processing environment. Serotype 1/2a strains make up more than 50% of the total isolates recovered from food and environment, while serotype 4b strains are most often associated with major outbreaks of human listeriosis. Using a microplate assay with crystal violet staining, we examined biofilm formation by 18 strains of each serotype in tryptic soy broth with varying concentrations of glucose (from 0.25% to 10.0%, w/v), sodium chloride (from 0.5% to 7.0%, w/v) and ethanol (from 1% to 5.0%, v/v), and at different temperatures (22.5 °C, 30 °C, and 37 °C). A synergistic effect on biofilm formation was observed for glucose, salt and temperature. The serotype 1/2a strains generally formed higher density biofilms than the 4b strains under most conditions tested. Interestingly, most serotype 4b strains had a higher growth rate that the 1/2a strains, suggesting that growth rate may not be directly related to the capacity in biofilm formation. Crystal violet was found to stain both bacterial cells and biofilm matrix material. The enhancement in biofilm formation by environmental factors was apparently due to the production of extracellular polymeric substances instead of accumulating viable biofilm cells.