Motility, biofilm formation, apoptotic effect and virulence gene expression of atypical Salmonella Typhimurium outside and inside Caco-2 cells

Disease outbreaks related to waterborne pathogen contamination throughout the world as well as challenges that lie ahead for addressing persistent infection are of renewed interest. In this research, we studied the effects of prolonged exposure of Salmonella enterica serovar Typhimurium to the cues encountered in the extracellular environment particularly in seawater microcosm on bacterial virulence and subsequent infection in Caco-2 cells. Our data show a significant difference in biofilm formation, swimming and swarming motilities between normal and stressed cells of S. Typhimurium under differing NaCl conditions (P < 0.05). Interestingly, adhesion, invasion and apoptotic activity to Caco-2 epithelial cells were determined during infection with normal and stressed Salmonella. Furthermore, we compared the expression of SPI-1 virulence genes (sopA, sopB, sopD, sopE2 and hilA) of normal and stressed S. Typhimurium in response to salt conditions encountered in the extracellular environment in LB broth and after epithelial cell exposure. The interest of the present study is due to the fact that to investigate the bacterial survival strategies during its movement from the natural surroundings to the host cell is fundamental to our understanding of the infection process during the host-pathogen interactions.