Use of physical methods in microbial control:

Heat:

Heating is still one of the most popular ways to destroy microorganisms. Fire and boiling water have been used since the time of Greeks for sterilization and disinfection. Either moist heat or dry heat may be applied. Moist heat kills viruses, bacteria and fungi. Exposure to boiling water for 10 min is sufficient to kill or destroy vegetative cells and eukaryotic spores., but not enough to kill or destroy bacterial endospores, hence boiling does not sterilize but can be used for disinfection of drinking water and objects not harmed by water. In order to destroy bacterial endospores, moist heat sterilization must be carried out at temperatures above 100°C and this requires the use of saturated steam under pressure. This can be carried out with an autoclave (Chamberland, 1884).Water is boiled to produce steam, which is released through the jacket and into the autoclave's chamber. Hot, saturated steam enters the chamber and the desired temperature and pressure, usually 121°C and 15 pounds is reached (Fig. 9). At this temperature saturated steam destroys all vegetative cells and endospores. Moist heat is thought to kill so effectively by degrading nucleic acids and by denaturing enzymes and other essential proteins. It also may disrupt cell membranes.

Fig. 9 . View of an autoclave