Indicators in moist heat sterilization

Physical Indicator: In this process, a temperature record chart is made for each sterilization cycle with dry heat sterilization. This chart of the batch documentation is compared against master temperature records.

Chemical Indicator: It is based on the ability of heat to alter the chemical or physical characteristics of a variety of chemical substances. This change should take place only when the satisfactory condition for sterilization prevails. Thus, confirming that the sterilization cycle has been successfully completed chemical indicators generally undergo melting or color change.

Biological Indicator: Spores of B. Steareothermophylus in sealed ampoules of culture medium are used for moist heat sterilization monitoring and these may be incubated directly at 55°C, thus eliminating the need for aseptic transfer (Table).

Table: Indicators in moist heat sterilization

Indicator	Sterilization Method	Principle	Device	Parameter monitored
Physical	Moist heat	Temperature recording charts	Temperature recording charts	Temperature
Chemical	Moist heat	Temperature-sensitive colored solution	Browne’s tube	Temperature, Time
		Steam sensitive chemical	A device that is impregnated into a carrier material.	Saturated steam
Biological	Moist heat	Temperature sensitive microbes	Bacillus Stearothermophilus	D-value