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In What Bacteria Does Salt Act As a Preservative?

Once so highly prized that workers were paid their wages in it (hence the word salary), salt is still one of the most commonly used food preservatives in the world. Salting meats and other perishables inhibits the growth of a wide variety of bacteria, allowing people to store food for long periods of time without it going bad. Salt is effective for several reasons and it acts against bacteria in several different ways.

  1. Gram Negative Bacteria

    • Environments that are highly salty have growing conditions that favor gram positive bacteria instead of gram negative bacteria. Most pathogenic bacteria, like E.Coli and Salmonella, are gram negative. Furthermore gram positive bacteria compete with gram negative bacteria and fight them off, which is one of the reasons your body produces salty sweat. Many probiotics (bacteria that are good for you) are actually gram positive, like the lactic acid bacteria in fermented milk products.

    Dehydration

    • If the concentration of salt is high enough, it will withdraw water from inside the cell of bacteria, causing them to wither and die. Although some bacteria have evolved highly resistant cell walls so that they can thrive in highly salty environments, it is nearly impossible for bacteria to thrive on pure salt. Highly salted foods maintain a very dry environment that doesn't allow the growth of most bacteria.

    Osmotic Pressure

    • Because bacteria live in a watery environment, the pressure of the water outside of their cell wall has a profound effect on the way they grow, mobilize and thrive. Water with a high salt content, like brine, makes it almost impossible for bacteria to draw water, which they need for food and nourishment, into themselves. Highly salted water (over 10%) usually inhibits all pathogenic bacteria from growing, which is why pickling is such an effective means of food preservation.

    Electroylte Imbalances

    • Electrolytes are electronically charged ions that allow for the exchange of energy within cells. When electrolytes become unbalanced or deficient, cells cannot function properly. Salt actually is an electrolyte, and when the bacterial cells are exposed to a highly salty environment, it causes an electrolyte imbalance within the cell itself.

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