Effect of Nutrients on Biofilm Formation by Listeria monocytogenes on Stainless Steel

The effect of nutrients on the development of biofilms by Listeria monocytogenes was investigated using semicontinuous culture in a chemically defined minimal medium (modified Welshimer's broth, MWB). Inoculated slides were used for the development of biofilms for 12 days at 21°C under various nutrient conditions. Biofilms were quantified by measuring the percentage of area covered by cells, using computerized image analysis. MWB allowed slow development of Listeria monocytogenes biofilms. Glucose levels between 1 and 20 g/l did not affect biofilm development. A reduction or increase in phosphate level from that occurring in MWB (37.52 g/l) reduced biofilm development. The degree to which biofilms initially developed was associated with amino acid concentration within the range of 0.12 to 6 g/l; however, after 12 days of incubation, the amount of biofilm produced was not affected by amino acid concentration. Replacement of amino acids in MWB with tryptone initially enhanced biofilm development, but the effect was not significant after 12 days of incubation. Of five carbohydrates tested, mannose and trehalose enhanced biofilm development.