The surface physicochemical properties of Listeria monocytogenes LO28 under different conditions (temperature and growth phase) were determined by use of microelectrophoresis and microbial adhesion to solvents. The effect of these parameters on adhesion and biofilm formation by L. monocytogenes LO28 on hydrophilic (stainless steel) and hydrophobic (polytetrafluoroethylene [PTFE]) surfaces was assessed. The bacterial cells were always negatively charged and possessed hydrophilic surface properties, which were negatively correlated with growth temperature. The colonization of the two surfaces, monitored by scanning electron microscopy, epifluorescence microscopy, and cell enumeration, showed that the strain had a great capacity to colonize both surfaces whatever the incubation temperature. However, biofilm formation was faster on the hydrophilic substratum. After 5 days at 37 or 20°C, the biofilm structure was composed of aggregates with a threedimensional shape, but significant detachment took place on PTFE at 37°C. At 8°C, only a bacterial monolayer was visible on stainless steel, while no growth was observed on PTFE. The growth phase of bacteria used to inoculate surfaces had a significant effect only in some cases during the first steps of biofilm formation. The surface physicochemical properties of the strain are correlated with adhesion and surface colonization.

The proteome of a Listeria monocytogenes strain isolated from a food plant was investigated to study the differential protein pattern expressed by biofilms and planktonic bacteria. The approach used in this study was a combination of two-dimensional electrophoresis, matrix-assisted laser desorption ionization-time of flight and database searches for the protein identification. Thirty-one proteins varied significantly between the two growth conditions. Twenty-two and nine proteins were up- and down-regulated respectively and nine proteins were successfully identified. The variations of the protein patterns indicated that the biofilm development is probably controlled by specific regulation of protein expression involved at various levels of cellular physiology.

Escherichia coli 0157:H7 biofilms were studied by a new method of cultivation in order to identify some of the proteins involved in the biofilm phenotype. A proteomic analysis of sessile or planktonic bacteria of the same age was carried out by two-dimensional electrophoresis, matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF-MS) and database searching. Comparison of two-dimensional gels showed clear differences between protein patterns of sessile and planktonic cells. Fourteen proteins increased in biofilms, whereas three decreased. From these 17 proteins, 10 were identified by MALDI-TOF-MS and could be classified into four categories according to their function: (1) general metabolism proteins (malate dehydrogenase, thiamine-phosphate pyrophosphorylase), (2) sugar and amino acid transporters (D-ribose-binding periplasmic protein, D-galactose-binding protein, YBEJ), (3) regulator proteins (DNA starvation protein and H-NS) and (4) three proteins with unknown function. The results of this study showed that E. coli O157:H7 modified the expression of several proteins involved in biofilm growth mode.

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