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 hypo-tonic 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.作者: yuk郁 時間: 2012-2-29 15:58
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