Different bacteria like to grow at different temperatures. Thus, a microbiologist will incubate a particular strain of bacteria at its optimal temperature so that he can study it when it is healthy. By changing the temperature, he can study the bacteria while they are stressed. Organisms that grow best at human body temperature, which is approximately 37 degrees Celsius (98.6 degrees Fahrenheit), are called mesophiles. Those that grow in hot temperatures between 40 to 70 degrees Celsius (104 to 158 degrees Fahrenheit) are called thermophiles. Those that grow at hot temperatures above 80 degrees Celsius are hyperthermophiles. Those that live in very cold conditions are called psychrophiles.
