Impact of long-term starvation on adhesion to and biofilm formation on stainless steel 316 L and gold surfaces of Salmonella enterica serovar Typhimurium

The objective of this study was to evaluate the effect of 3-year starvation in seawater microcosms on adhesion to and biofilm formation of two Salmonella enterica serovar Typhimurium strains on model stainless steel 316 L and gold surfaces. The bacteria were characterized in terms of morphological alteration, electrophoretic mobility, and affinity to various solvent interfaces. Scanning electron micrographs showed the appearance of coccoid and elongated cells after starvation. All stressed cells were characterized by a hyperflagellation, a significant increase in the global surface charge, and a conservation of their hydrophilic character. Epifluorescence microscopy highlighted an increase in the levels of adhered cells to stainless steel and gold surfaces after starvation stress. Confocal laser scanning microscopy produced evidence of variability between the three-dimensional biofilm architectures of the control and stressed cells on gold compared to stainless steel. The results obtained so far led us to hypothesize that the pervasiveness of nutrient deficiency in natural environments may generate new adaptation strategies for long-term starved Salmonella Typhimurium and probably create protection against other types of stress. The stress adaptation mechanisms identified in this study may induce a genetic instability and change virulence state of starved bacteria. This fundamental study provides information which may aid in the development of sanitation programs for effective pathogen removal in the food industry or from medical devices. The task is certainly complex given that several concomitant physicochemical parameters affect the adhesion to and biofilm formation on model surfaces of stressed bacteria.