Effect of low-nutrient seawater on morphology, chemical composition, and virulence of Salmonella typhimurium.
The response of Salmonella typhimurium to low nutrient levels was determined by measuring the concentrations of lipids, carbohydrates, DNA, RNA, and proteins over a 32-day starvation period. Ultrastructural integrity was observed by transmission electron microscopy. Lipid and carbohydrate content of bacterial cells rapidly declined within the first 16 days, while DNA and proteins exhibited a more gradual decline over the 32 days of starvation. In contrast, RNA content did not decrease appreciably upon nutrient starvation. Structural damage occurred especially after 16 days of starvation. After 32 days of nutrient deprivation, we recorded degenerative cellular forms, a coccoidal cell shape, a decrease in cellular volume, and the loss of the three-layered outer membrane. The morphological and structural alterations correlated with virulence in infected animals. We observed a decrease in virulence of S. typhimurium after 9, 16, and 32 days of starvation, reaching a maximal decrease after 32 days of nutrient deprivation. The decrease in virulence correlated to surface hydrophobicity alterations, adherence to eukaryotic cells, and phagocytosis.