Fundamentals of Microbiology

Moist Heat

 The sterilizing effect of moist heat is due to coagulation of proteins. Moist heat can be generated by boiling water, using free flowing steam (at 100ºC -maintaining atmospheric pressure) or steam under pressure. This is done by autoclaving.  Bacteria are more readily killed by moist heat than dry heat.  The safe condition for sterilization is to use steam at 121^oC for 15 min.  This is suitable for culture media, aqueous solution, treatment of discarded cultures and specimens etc. The boiling point of water increases with increasing pressure of steam. Therefore, such a treatment is very effective against all bacteria including spores. Although, boiling water and free flowing steam are used for heat treatment they are not generally effective against spores of bacteria.