Pathogenic mono-species biofilm formation on stainless steel surfaces: Quantitative, qualitative, and compositional study

The aims of this study were, first, to determine Listeria monocytogenes, Salmonella enterica, ser. Typhimurium, and Staphylococcus aureus biofilm counts, structure, and their composition in macromolecules by direct epifluorescence microscopy (DEM); and second, to evaluate the distribution of the components of the produced biofilms through 3D representations obtained by confocal laser scanning microscopy (CLSM). Results showed that all assessed strains have a high capacity to generate biofilms, with counts greater than 7 log CFU cm⁻² in all cases. The highest and lowest survival percentages were obtained by S. aureus with 94.13 ± 1.77% and S. Typhimurium with 60.31 ± 4.45%, respectively. Biofilm matrix composition in macromolecules was as follows: (a) L. monocytogenes: proteins 83.35 ± 5.81%, polysaccharides 10.98 ± 5.77%, and extracellular DNA 5.67 ± 2.5%; (b) S. Typhimurium: 83.37 ± 3.35%, 0.68 ± 0.77%, and 15.95 ± 3.39%, respectively; and (c) S. aureus: 82.55 ± 2.39%, 8.48 ± 2.07%, and 8.97 ± 2.27%, respectively. The qualitative analysis of the 3D representations of the biofilms formed by the pathogens modelized showed no homogeneity and/or ordered distribution of their components within the biofilm architecture. These findings could lead to the development of addressed cleaning and disinfection alternatives.