Bacteria can grow under very diverse conditions, which is why they are found nearly everywhere on Earth. Although bacteria are good at adapting to their environments, certain conditions promote bacterial growth more than others. These conditions include temperature, moisture, oxygen and pH. Knowing and avoiding these optimal conditions can help prevent bacterial growth, bacterial infections and food poisoning.
Bacteria thrive in warm temperatures, especially those close to body temperature. The human body, therefore, provides an ideal environment for many types of bacteria to grow. Certain strains of bacteria, however, can grow at lower or higher temperatures. Since ideal temperature is crucial for the growth of any given species of bacteria, food must be handled appropriately to avoid food poisoning. In most cases -- but not all -- refrigeration or freezing of food is sufficient to prevent disease-causing bacteria, such as staphylococcus, from growing. Thoroughly cooking meats to the correct internal temperature is also important to kill any harmful bacteria -- such as Salmonella and E. coli -- that may be present in the food.
Bacteria need water to grow and will die without a water source. Moist areas are particularly prone to bacterial growth, such as bathrooms and kitchens. Water content in food also provides an excellent environment for bacteria to grow. Certain foods can be freeze-dried, which removes most of the water and can allow for longer storage of the food without bacterial growth. Moist tissues in the body, such as the mouth and nose, provide an excellent source of moisture for bacteria and are particularly prone to bacterial growth.
The presence of oxygen can greatly affect the growth of bacteria. Although some bacteria can survive without oxygen, many types of bacteria require oxygen to grow. This is why many commercial foods are vacuum-sealed. Once you open a food product and break this seal, exposure to the environment and oxygen limits the shelf life of the product before it spoils. Keeping food properly sealed while it is being stored is a good preventive measure against bacterial growth, because it restricts the amount of oxygen. Sealing properly is also important when doing home canning for similar reasons.
The pH of an environment -- a measure of its acidity or alkalinity -- is important for bacterial growth. Most strains of bacteria prefer to grow in conditions with neutral pH, similar to the pH of the human body. Some strains of bacteria, however, can live in slightly more acidic or more alkaline conditions. Cleaning solutions are typically highly acidic or basic, which kills bacteria, because they cannot survive at these extremes of pH. The acidity of food is also important for bacterial growth. More acidic foods can typically be stored longer without spoiling. Preserving agents that increase the acidity of food are commonly added to help prevent bacterial growth and allow for longer storage.