Explain the Physical Methods to Control Microorganisms?

The physical methods to control microorganisms involve heat, filtration or radiations. Figure illustrates these methods. Temperature influences microorganisms by altering their enzyme systems. Low temperature, you may recall studying in the theory Course, inactivates the enzymes while high temperature destroys them. Heat is commonly employed for controlling microorganisms. Both moist heat and dry heat can be used for this purpose. Moist heat results in coagulation of proteins and degrades nucleic acid and may even disrupt cell membrane.

Moist heat has more penetrability than dry heat and kills the cells more rapidly that too at a lower temperature. Microbes exhibit difference in their resistance to moist heat. Generally, bacterial spores require temperature above 100°C for destruction. Moist heat can either sterilize or disinfect the object depending upon the temperature employed. Moist heat can be used either

(1) at temperature <100° C (pasteurization-used to remove pathogens),

(2) as free flowing steam at 100° C (by boiling or tyndallisation) or

(3) by saturated steam under pressure (autoclaving).