Differences between clinical and food isolates of Listeria monocytogenes in biofilm formation

Pathogenic microorganisms such as Listeria monocytogenes are known to form biofilms. The risk of contamination of food products in the food industry and growth on medical devices in the clinical environment is a cause of concern. The objectives of this work were to examine and compare biofilm formation by food and clinical isolates of L. monocytogenes. A total of 376 L. monocytogenes strains, 258 isolated from various food products and 118 clinical isolates, were investigated with respect to their ability to form biofilms in 96-wells microtiter plates, at 4 degrees C during 5 days and at 37 degrees C during 24h. Statistically significant differences (p < 0.01) were found between biofilm formation at 4 degrees C or at 37 degrees C. At 4 degrees C, statistically significant differences between clinical and food isolates were observed (p < 0.01). Although being classified as weak producers, more food isolates produced biofilms than clinical isolates. Statistically significant differences (p < 0.01) between clinical and food isolates were also observed at 37 degrees C. However, at this temperature, more clinical isolates produced biofilms than food isolates; 4% and 0.4% of the clinical and food isolates investigated, respectively, were classified as strong biofilm formers. Biofilm production was demonstrated to differ between clinical and food isolates, but these differences were temperature dependent.