Brigitte Carpentier

The quantity of microorganisms that may be transferred to a food that comes into contact with a contaminated surface depends on the density of microorganisms on the surface and on the attachment strengths of the microorganisms on the materials. We made repeated contacts between pieces of meat and various surfaces (stainless steel and conveyor belt materials [polyvinyl chloride and polyurethane]), which were conditioned with meat exudate and then were contaminated with Listeria monocytogenes , Staphylococcus sciuri , Pseudomonas putida , or Comamonas sp. Attachment strengths were assessed by the slopes of the two-phase curves obtained by plotting the logarithm of the number of microorganisms transferred against the order number of the contact. These curves were also used to estimate the microbial population on the surface by using the equation of A. Veulemans, E. Jacqmain, and D. Jacqmain (Rev. Ferment. Ind. Aliment. 25:58-65, 1970). The biofilms were characterized according to their physicochemical surface properties and structures. Their exopolysaccharide-producing capacities were assessed from biofilms grown on polystyrene. The L. monocytogenes biofilms attached more strongly to polymers than did the other strains, and attachment strength proved to be weaker on stainless steel than on the two polymers. However, in most cases, it was the population of the biofilms that had the strongest influence on the total number of CFU detached. Although attachment strengths were weaker on stainless steel, this material, carrying a smaller population of bacteria, had a weaker contaminating capacity. In most cases the equation of Veulemans et al. revealed more bacteria than did swabbing the biofilms, and it provided a better assessment of the contaminating potential of the polymeric materials studied here.

An enzyme-linked lectinsorbent assay (ELLA) was developed for quantification and characterization of extracellular polysaccharides produced by 1- and 4-day biofilms of 10 bacterial strains isolated from food industry premises. Peroxidase-labeled concanavalin A (ConA) and wheat germ agglutinin (WGA) were used, as they specifically bind to saccharide residues most frequently encountered in biofilms matrices: d -glucose or d -mannose for ConA and N -acetyl- d -glucosamine or N -acetylneuraminic acid for WGA. The ELLA applied to 1- and 4-day biofilms colonizing wells of microtiter plates was able to detect that for Stenotrophomonas maltophilia and to a lesser extent Staphylococcus sciuri , the increase in production of exopolysaccharides over time was not the same for sugars binding with ConA and those binding with WGA. Differences in extracellular polysaccharides produced were observed among strains belonging to the same species. These results demonstrate that ELLA is a useful tool not only for rapid characterization of biofilm extracellular polysaccharides but also, in studies of individual strains, for detection of changes over time in the proportion of the exopolysaccharidic component within the polymeric matrix.

The adhesion and subsequent development of Listeria monocytogenes on stainless steel was studied in the absence and in the presence of a Staphylococcus sciuri biofilm. In the three growth media studi...