The salt water sets up a hypertonic environment; water rushes out of the bacterium by osmosis, killing the bacterium. So it is not a question of pressure exerted on red blood cell walls, but rather the pressure exerted on the bacterial cell wall. That was the simple answer but for a more complex answer try this one which I won't type out for you. I'll just paste it for you. I could ask "Are you smarter than a 15 year old?" lol!!! name yona kim status student age 15 Question - How and why exactly does sodium chloride affects microorganisms? or bacteria? In another word, how does preservative(salt) works? All organisms with a semipermeable membrane are subject to osmotic pressure, or the effect of water moving in and out of the cell. Bacteria have a cell membrane and a cell wall. Bacteria must live in an aqueous (watery) environment. Most often this is a hypotonic environment, in other words, the concentration of water outside the cell is greater than the concentration of water inside the cell. This causes the net movement of more water into the cell than outside. If the bacterium did not have a cell wall, this could cause the cell to burst. (In fact, many antibiotics work by causing an ineffective cell wall to be made, which allows the bacterial cell to burst under water pressure). So why does salt work as a preservative? Because when the outside environment around a cell is salty, then the concentration of water in the solution is less than inside the cell and water tends to leave the cell. This causes the cell to dehydrate, which eventually kills the cell. By subjecting bacteria to a salty environment, it keeps them from growing. Some bacteria however, have adapted to living in salty environments, such as Staph. bacteria a common skin inhabitant. Your skin tends to be salty-this is one way your body protects you against bacteria on your skin. But even Staph can't live in highly salty surroundings, such as salted foods like ham, etc. van hoeck ========================================================= The major effect of salt as a preservative is that it withdraws water from microorganisms if the external salt concentration is high enough. The microbes would shrivel and die, spores would not be killed but would not be able to germinate. High concentrations of sugar have the same effect. The physical term for this is hypertonic tension. Some bacteria have learned to cope with high salt concentrations and can live in saline waters. Fortunately they are not pathogenic (do not cause disease) so we need not worry about them. Dr. Wassenaar Curator of the Virtual Museum of Bacteria www.bacteriamuseum.org