Describe the conditions favorable to the growth of bacteria in food.
Bacteria are everywhere. Some are beneficial, such as those used to make fermented dairy and meat products. Others cause spoilage. And, a small percentage are harmful or pathogenic.
Unlike animals and plants that are composed of many cells, bacteria are single-celled organisms. Each bacterium cell is self-sufficient and so is able to live independently. Bacteria come in a variety of shapes and are impossible to see without a microscope. Because they are about 1/25,000th of an inch long, they must be magnified about 1,000 times to be seen. For example, about 400 million bacteria clumped together would be about the size of a grain of sugar.
When bacteria grow, they increase in numbers not in size. This process is called cell division (or doubling). Under ideal conditions, the number of bacteria can double every 30 minutes. Therefore, one becomes two, two become four, four become eight, and so on. If you start with one bacterial cell, after 12 hours there would be as many as 33,000,000. The rate at which bacteria grow is different for each type or organism and is affected by many factors.
Factors Affecting Microbial Growth
Many factors affect bacterial growth but the most important ones are:
Although each of the major factors listed above plays an important role, the interplay between the factors ultimately determines whether a microorganism will grow in a given food. Often, the results of such interplay are unpredictable, as poorly understood synergism or antagonism may occur. An advantage is taken of this interplay with regard to preventing the outgrowth of C. botulinum. Food with a pH of 5.0 (within the range for C. botulinum) and an aw of 0.935 (above the minimum for C. botulinum) may not support the growth of this bacterium. Certain processed cheese spreads take advantage of this fact and are therefore shelf stable at room temperature even though each individual factor would permit the outgrowth of C. botulinum.
Therefore, predictions about whether or not a particular microorganism will grow in a food can, in general, only be made through experimentation. Also, many microorganisms do not need to multiply in food to cause disease.