Temperature is one of the important factors affecting the process of growth in bacteria, as it has a bearing on chemical reactions. The temperature at which the maximum growth occurs is known as the optimum temperature. Based on the temperature at which the maximum growth occurs, the bacteria are divided into three main categories:

1) Thermophiles: The species of bacteria which grows rapidly between 45-65"C, although they may grow anywhere between 45-75°C.

2) Mesophiles: The species of bacteria which grows rapidly between 20-45"C, where the optimum temperature range is 30-40°C.

3) Psychrophiles: The bacterial species which grows rapidly at 0°C (and even below), and have an optimum temperature range of 10-20°C.