Unraveling Dual Environmental Stresses (How Photo and Salt Challenge Diarrhea-Causing Bacteria's Adaptation And Defense Mechanisms)

In this research, the effect of light and salt stress on bacteria that cause diarrhea, such as Shigella flexneri, EHEC O157:H7, and Salmonella Typhi, was studied. Light stress resulting from exposure to ultraviolet rays causes changes in the physiological and chemical composition of the cell, which leads to a reduction in the growth rate of bacteria, as bacterial density decreased by up to about 36.4% in Salmonella Typhi compared to the control group. In contrast, salt stress, represented by a 3% concentration of sodium chloride, shows a defensive effect of increasing biofilm formation; EHEC O157:H7 recorded a 100% increase in biofilm production as a cell protection mechanism, the effect of combined stress of light and salt on the movement of bacteria was also studied, showing that the movement of the three species decreased by a constant rate of up to 60% when exposed to double pressure. At the genetic level, the results showed an increase in the expression of some genes related to the stress response such as the rpoS gene and the stx toxin production gene, while a decrease was observed in the fliC movement gene, which indicates a shift in the cells' strategy towards strengthening defense mechanisms and conserving energy. Regarding the effect of salt stress, the expression of the osmY gene responsible for the osmotic response increased, with an increase in the ampC gene for antibiotic resistance and a decrease in the expression of the ipaH gene associated with plasmidic influence, the analyzes revealed that sensitivity to antibiotics changed, as the sensitivity of bacteria to ampicillin decreased compared to ciprofloxacin. Finally, microscopic studies showed shorter cell length under stress conditions compared to the control group. The study offers deep insight into the mechanisms of bacterial adaptation to changing environmental conditions, aiding in the development of innovative and effective infection prevention strategies.