The Three Requirements of Pathogens

The Three Requirements of Pathogens

Pathogens thrive when three basic living conditions are readily available. They are protein, water and appropriate pH. A large percentage of foods typically contain these three elements in ratios favorable to the rapid growth of pathogens. The greater the abundance of protein and water and the more favorable the pH, the higher the likelihood that foods will become contaminated.

In addition, some bacteria do best with a good supply of oxygen, others when oxygen is absent, Some can get along either way. The handling procedures on cooling, reheating and thawing help to prevent any single condition from becoming so predominant that it will favor the pathogen's growth and reproduction.


Most foods contain some protein. Meats, fish, poultry and eggs are among the foods with the greatest percentage of protein, making them and prepared foods containing them, highly susceptible to food poisoning and intoxication. But, grains and legumes also contain protein in significant quantities. They become especially vulnerable once cooked. Rice and potatoes are among the most likely carriers of disease. Vegetables contain very small amounts of protein, and fruit contain very little if any protein at all.


Foods that are moist enough to be soft and easy to chew are also moist enough to support the growth of many types of pathogens. There are some foods that are naturally 'dry' and have a lesser chance of becoming infected; example certain root vegetables have a relatively low moisture content. Other foods, once processed, lose much of their moisture; very hard cheeses such as Romano or Parmesan cheeses; dried, salted, or preserved foods such as olives and hams; nuts and seeds, and uncooked grains, cereals, and meals. These are the foods that we treat as "non-perishables", a recognition of the fact that they can be stored at room temperature without fear of immediate loss of quality or wholesomeness.

Moderate pH

The pH of most foods falls within a range considered "moderate'; a state that makes foods attractive for the growth and reproduction of many different types of micro-organisms. A substance that is extremely acid (example lemon juice) will be closer to a value of zero. Those that are extremely alkaline (example baking soda) will measure closer to 14. Most foods tend to fall within range of about 4 to 10. Foods that are either more acidic or more alkaline than that will generally no longer be susceptible to micro-organisms. Vinegar, lemon or lime juice, and other very tart and sour-tasting foods are acid; baking soda, alum, cream of tartar are bitter tasting and cause the mouth to pucker, these items are alkaline. We use this general principle to preserve foods when we pickle, salt, or brine them in order to change their pH level to above 10 or below 4, increasing the shelf life of the food.

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